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HomeMy WebLinkAboutCT 02-14-06; BRESSI RANCH PA12 UNIT 6; SUPPLEMENTAL GEOTECHNICAL INVESTIGATION; 2001-03-14SUPPLEMENTAL GEOTECHNICAL INVESTIGATION FOR MASS GRADING, BRESSI RANCH, CARLSBAD, CALIFORNIA March 14, 2001 ProjectNo. 971009-005 Prepared For: LENNAR HOMES 5780 Fleet Street, Suite 320 Carlsbad, Califomia 92008 Leighton and Associates, Inc. A LEIGHTON GROUP COMPANY 4 Leighton and Associates, Inc. A LEIGHTON GROUP COMPANY To: March 14, 2001 ProjectNo. 971009-005 Lennar Homes 5780 Fleet Street, Suite 320 Carlsbad, Califomia 92008 Attention: Mr. Jim Urbina Subject: Supplemental Geotechnical Investigation for Mass Grading, Bressi Ranch, Carlsbad, Califomia In accordance with your request, we have performed a supplemental geotechnical investigation for the Bressi Ranch property located southeast of the intersection of El Camino Real and Palomar Auport Road in Carlsbad, Califomia. The purpose of this report was to update the results of our preliminary geotechnical report for the site (Leighton, 1997) and to evaluate the existing geologic and geotechnical aspects of the proposed mass grading of the site relative to the latest 200-scale tentative tract map/grading plans. This report presents the results of our supplemental subsurface investigation and geotechnical analysis, and provides a summary of our conclusions and recommendations relative to the mass grading of the site. Based on the results of our supplemental investigation and review of the previous geotechnical reports pertinent to the subject site, the proposed development of the site for commercial and residential uses is considered feasible from a geotechnical standpoint provided the recommendations summarized in this report are implemented during the site grading operations. It should be noted that additional geotechnical evaluation of the site (including additional field studies, laboratory testing, and slope stability analysis) and a grading plan review will be needed after more detailed grading plans (i.e. 40-scale grading plans) for the different planning areas of the site are developed. If you have any questions regarding our report, please contact this office. We appreciate this opportunity to be of service. Respectfully submitted, LEIGHTON AND ASSOCIATES, INC. Tim J. Lawson, RCE 53388 Principal Consulting Engineer Randall K. Wagn%r, CEG 1612 Director of Geology Distribution: Addressee Lennar Homes, Attention: Mr. Dale Greenhaigh PDC, Attention: Ms. Marina Wurst 3934 Murphy Canyon Road, Suite B205 • San Diego, CA 92123-4425 858.292.8030 • Fax 858.292.0771 • www.leightongeo.com 4971009-005 TABLE OF CONTENTS Section Page LO INTRODUCTION 1 1.1 PURPOSE AND SCOPE OF SERVICES 1 1.2 SrrE DESCRIPTION 1 1.3 PROPOSED DEVELOPMENT 3 1.4 SUPPLEMENTAL SURFACE INVESTIGATION AND LABORATORY TESTING 3 2.0 GEOTECHNICAL CONDITIONS 5 2.1 REGIONAL GEOLOGY 5 2.2 SITE-SPECIFIC GEOLOGY 5 2.2.1 Documented Fill Soils (Map Symbol -Af) 5 2.2.2 Undocumented Fill Soils (Map Symbol - Afu) 5 2.2.5 Topsoil (Unmapped) 6 2.2.4 Alluvium/ Colluvium, Undifferentiated (Map Symbol - Qal/Qcol) 6 2.2.5 Landslide Deposits (Map Symbol - Qls) 6 2.2.6 Santiago Formation (Map Symbol -Ts) 7 2.3 GEOLOGIC STRUCTURE 8 2.4 FAULTING 8 2.5 SEISMIC CONSIDERATIONS 9 2.5. / Liquefaction and Dynamic Settlement 9 2.5.2 Uniform Building Code Seismic Parameters 9 2.6 GROUNDWATER 10 2.7 ENGINEERING CHARACTERISTICS OF ON-srrE SOILS 10 2.7.1 Expansion Potential 10 2.7.2 Soluble Sulfate Content 11 2.7.3 Excavation Characteristics 11 2.7.4 Earthwork Shrinkage and Bulking 11 2.8 SLOPE STABILrrY 12 2.9 SETaEMENT OF DEEP FILLS 12 3.0 CONCLUSIONS 13 4.0 RECOMMENDATIONS 15 4.1 EARTFTWORK 15 4.1.1 Site Preparation 75 4.1.2 Removal and Recompaction of Unsuitable Soils 15 4.1.3 Excavations 17 4.1.4 Cut/Fill Transition Conditions 17 4.1.5 Fill Placement and Compaction 17 4.1.6 Settlement of Deep Fills 77 4.1.7 Expansive Soils and Selective Grading 18 4 Leighton 4971009-005 TABLE OF CONTENTS (Continued) Section Page 4.2 SLOPE STABILrrY 18 4.2.1 Deep-Seated Stability 19 4.2.2 Surficial Stability 27 4.3 CONTROL OF GROUND WATER AND SURFACE WATERS 21 4.3.1 Canyon Subdrains 22 4.3.2 Buttress and Stability Fill Subdrains 22 4.3.3 Cut Slope Seepage Conditions 22 4.4 SETTLEMENT MONTFORING 23 4.5 SURFACE DRAINAGE AND LOT MAINTENANCE 23 4.6 GRADED SLOPES 23 4.7 PLAN REVIEW AND CONSTRUCTION OBSERVATION 24 5.0 LIMITATIONS 25 FIGURES FIGURE 1 - SITE LOCATION MAP - PAGE 2 FIGURES 2 THROUGH 14 - GEOLOGIC CROSS-SECTIONS A-A' THROUGH M-M' - IN POCKET TABLES TABLE 1 - GEOTECHNICAL SUMMARY OF EXISTING LANDSLIDES - REAR-OF-TEXT TABLE 2 - EARTHWORK SHRINKAGE AND BULKING ESTIMATES - PAGE 11 TABLE 3 - SLOPE STABILITY SOIL PARAMETERS - PAGE 19 PLATES PLATE 1 - GEOTECHNICAL MAP - IN POCKET PLATE 2 - REMEDLAL GRADING MAP - IN POCKET APPENDICES APPENDIX A - REFERENCES APPENDIX B - BORING AND TRENCH LOGS APPENDIX C - LABORATORY TEST PROCEDURES AND TEST RESULTS APPENDIX D - GENERAL EARTHWORK AND GRADING SPECIFICATIONS FOR ROUGH-GRADING - 11 -4 Leighton 971009-005 1.0 INTRODUCTION 1.1 Purpose and Scope of Services This report has been prepared in accordance with your request and presents the results of our supplemental geotechnical investigation of the Bressi Ranch for mass grading purposes. Bressi Ranch is located southeast of the intersection of El Camino Real and Palomar Airport Road in the City of Carlsbad, Califomia (Figure 1). The purpose of this report was to update the results of our preliminary geotechnical report for the site (Leighton, 1997) and to evaluate the existing geologic and geotechnical aspects of the proposed mass grading of the site relative to the latest 200-scale tentative tract map/grading plans. Our scope of services included the following: • Review of pertinent available geotechnical literature (including previous geotechnical reports of Bressi Ranch, Rancho Carrillo, and La Costa - The Greens developments), geologic maps, and aerial photographs (Appendix A). • Reconnaissance and geologic mapping of the site. • A supplemental subsurface exploration program consisting of the excavation, sampling and logging of 8 large-diameter exploratory borings and 56 exploratory trenches across the site. The large-diameter borings and trenches were excavated to evaluate the characteristics of the subsurface soils. Logs of the borings and trenches are presented in Appendix B. Included in Appendix B, are logs of previous borings and trenches excavated by Leighton and others that are pertinent to the development of Bressi Ranch. • Laboratory testing of representative samples obtained during our preliminary and supplemental subsurface exploration programs (Appendix C). • Geotechnical analysis of the data accumulated during our supplemental investigation including seismic and slope stability analysis. • Preparation of this report presenting our findings, conclusions and recommendations including General Earthwork and Grading Specifications for Rough Grading (Appendix D) with respect to the proposed mass grading of the site. The approximate limits of the geologic units encountered and the boring and trench locations applicable to the development of the site are presented on the Geotechnical Map (Plate 1), Remedial Grading Map (Plate 2), and Cross- Sections A-A' through M-M' (Figures 2 through 14). The 200-scale Tentative Tract Map/Grading Plan (PDC, 2001b), was utilized as base map for the Geotechnical Map (Plate 1) and the Remedial Grading Map (Plate 2). 1.2 Site Description The subject property, with a total acreage of approximately 600 acres, is located southeast of the intersection El Camino Real and Palomar Airport Road in the City of Carlsbad, California (Figure 1). The site consists of an irregular-shaped piece of property bordered on the north by Palomar Airport Road, on the west by El Camino Real, on the southwest and south by the La Costa - The Greens property, and by the Rancho Carrillo development and Melrose Drive to the east. -1 Leighton NORTH BAS E MAP : Thomas Bros. GeoFinder for Windows, San Dlego County, 1995, Page 1127 0 1000 2000 4000 1 "=2,000' Scale in Feet Lennar / Bressi Ranch Carlsbad, California SITE LOCATION MAP Project No, 971009-005 Date March 20olLeightOI3ip,,rP No. 1 971009-005 Topographically, the site generally consists of a an east-west trending relatively large and flat ridgeline in the northem section of the site and a north-south trending central ridge in the south central portion of the site. The north-south trending central ridge is flanked by two large north-south trending drainages and associated tributaries fonning the gently sloping hillside and valley terrain in the south central portion of the property. A large east-west trending drainage is located in the far southem portion of the site. Elevations on the site range from a high of approximately 465 feet mean sea level (msl) in the north central portion of the site to a low of approximately 125 feet msl within the major east-west drainage in the southem portion of the site. Natural drainage is presently accomplished through a network of minor ravines and ultimately through the east-west trending canyon in the southem portion of the site. Vegetation on the site ranges from remnant vegetable crops, native grasses, and weeds on the flat ridge tops, wide canyon bottoms and on the hillsides; and minor to thick chaparral and trees (mainly on the steep hillsides and the narrow canyon bottoms) in the central and southwestem portions of the site. Man-made features on the site include: 1) a single-family residence in the central portion of the site; 2) a guard shack at the northem site entrance; 3) two building foundations and several relatively small detention basins (associated with prior farming activities); 4) existing SDG&E, water and sewer line easements crossing the site in westem, central and southem portions of the site; 5) several dirt roads which cross the property, and 6) fences along the perimeter of the property. 1.3 Proposed Development Detailed site grading and development plans were not available as of the date of this report. However, we understand that the proposed site development will include 13 planning areas across the site for light industrial, commercial, and residential purposes. In general, the light industrial planning areas are located in the northem portion of the site along Palomar Airport Road while the commercial planning areas are in the south and southeastem portion of the site. The residential planning areas are generally located in the central and southwestem portion of the site. Approximately 445 acres of the site will be graded while the remaining acreage will be left as open space. Preliminary calculations of the earthwork quantities indicate the grading will entail approximately 6 million yards of cut and fill material (PDC, 2001a). We also understand that development of the Bressi Ranch will include 1) constmction of Poinsettia Lane from its existing terminus at the southeastem portion of the site through the Bressi Ranch property and possibly to El Camino Real; 2) constmction of El Fuerte Road from Palomar Airport Road to existing portion of the road south of the Bressi Ranch Property; and 3) improvements to El Camino Real along the northwestem side of the Bressi Ranch Property. In addition, the development will include relatively large open space areas, interior streets, underground utilities, and other associated improvements. 1.4 Supplemental Surface Investigation and Laboratory Testing Our supplemental subsurface investigation consisted of the excavation, logging and sampling of 8 large-diameter borings (utilizing a bucket-auger drill rig) and the excavation of 56 exploratory trenches (in addition to the previously excavated 7 small-diameter borings, 21 large-diameter borings and 30 exploratory trenches The borings and trenches were excavated to a maximum depth of approximately 116 and 15 feet, respectively. The large-diameter borings were entered by our •3- Leighton 971009-005 geologist and down-hole logged. Logs of the borings and trenches are presented in Appendix B. The approximate locations of the borings are shown on the Geotechnical Map (Plate 1) and Cross- Sections A-A' through M-M' (Figures 2 through 14). Subsequent to the subsurface investigation, the borings and frenches were backfllled. Appropriate laboratory testing was performed on representative soil samples obtain during our preliminary and supplemental subsurface investigations. The laboratory tests included moisture/density determinations, Atterberg Limits (e.g. liquid limit and plastic limit), undisturbed and remolded direct shear, maximum dry density and expansion index tests. A discussion of the tests performed and a summary of the test results are presented in Appendix C. The density/moisture determinations of the undisturbed samples obtained from the borings are shown on the boring logs (Appendix B). -4- Leighton 971009-005 2.0 GEOTECHNICAL CONDITIONS 2.1 Regional Geologv The subject site is located within the coastal subprovince of the Peninsular Ranges Geomorphic Province, near the westem edge of the southem Califomia batholith. The topography at the edge of the batholith changes from the mgged landforms developed on the batholith to the more subdued landforms that typify the softer sedimentary formations of the coastal plain. Specifically, the site is underlain by the sedimentary units of the Tertiary-aged Santiago Formation. Subsequent to the deposition of this unit, erosion and regional tectonic uplift created the valleys and ridges of the area. Recent weathering and erosional processes have produced the Quaternary surficial units including alluvium, colluvium, landslide deposits, and topsoil that mantle the site. 2.2 Site-Specific Geology Formational materials of the Tertiary-aged Santiago Formation and surficial units consisting of landslide deposits, colluvium, alluvium, topsoil and artificial fill soils were encountered during our preliminary and supplemental investigations of the site. The areal distributions of the geologic units are presented on the Geotechnical Map (Plate 1). Our interpretation of the subsurface geologic conditions is also indicated on Geologic Cross Sections A-A' through M-M' (Figures 2 through 14). Each ofthe geologic units present on the site is described below (youngest to oldest). 2.2.1 Documented Fill Soils (Map Svmbol - Af) As observed, the documented fill was associated with prior grading of the Poinsettia Lane, El Fuerte Road, Palomar Airport Road, and Melrose Drive roadway alignments. As-graded Geotechnical Reports documenting the fill placement and grading operations (Appendix A) indicate the fill soils were placed at 90 percent relative compactions. However, we anticipate that the upper portion of the fill may have become desiccated and minimal removals (i.e. on the order of 1 to 5 feet) may be needed prior to the placement of additional fill. In addition, we anticipate the removal of unsuitable soils along the perimeter of the fills were not made outside a 1:1 (horizontal to vertical) projection from the existing toe-of-slope down to competent formational material undemeath the fill. 2.2.2 Undocumented Fill Soils (Map Svmbol - Afii) Undocumented fill soils were observed in a number of places on the site. The undocumented fill was generally associated with the grading of the on-site dirt roads, retention basins, and prior farming activities. These fill soils are estimated to range from 1 to 25 or more feet in depth, and generally consist of dry to damp, loose or soft sand and clay. All existing fills located within the limits of grading should be considered potentially compressible and unsuitable in their present state for structural support. The undocumented fill soils should be removed to competent formational material within the limits of the proposed grading. 5- Leighton 971009-005 2.2.3 Topsoil (Unmapped) The topsoil encountered during our field investigation mantles the majority of the site. The topsoil, as observed, consisted predominantly of a light-brown to brown, damp to moist, medium dense to stiff, sandy to silty clay and some clayey to silty sands. These soils were generally massive, porous, and contained scattered roots and organics. The unsuitable topsoil is estimated to be from 1 to 4 feet in thickness; however, localized areas of thicker accumulations of topsoil may be encountered during grading. 2.2.4 Alluvium/ Colluvium. Undifferentiated (Map Symbol - Qal/Qcol) Potentially compressible deposits of alluvium were encountered in the major and most of the tributary drainage courses on the site. In addition, our field investigation indicated that potentially compressible deposits of colluvium mantle the middle and lower portions of the on-site natural slopes (especially slopes comprised of the Santiago Formation claystone) and in the upper portions of the fributary drainage courses throughout the site. During our supplemental investigation, we did not differentiate the alluvial and colluvial deposits and therefore, these soils are mapped and presented as undifferentiated alluvium/colluvium on the geologic maps and cross-sections. As observed, these deposits typically consist of light orange-brown to brown sands, sandy clays and clayey sands that are porous and contain scattered organics. Both the alluvium and colluvium are considered potentially compressible in the present state. In general, the alluvium/colluvium is estimated to be 4 to 15 feet thick in the tributary canyons, however deeper accumulations may be present. The alluvium encountered in the proposed El Fuerte Road drainage and the main east-west rending canyon in the southem portion of the site (along proposed Poinsettia Lane) have alluvial thicknesses on the order of 40 to 50 or more feet. Relatively shallow ground water (generally less than 5 to 20 feet in depth) was observed in these alluvial soils. 2.2.5 Landslide Deposits (Map Svmbol - Qls) Several landslides have been identified within the subject property. The approximate limits of these landslides are shown on the Geotechnical Map (Plate 1) and the Remedial Grading Map (Plate 2). To aid in the discussion of the landslides, each landslide and/or landslide complex has been Numbered 1 through 24 (as indicated on the Remedial Grading Map). It should be noted that several of these landslides are outside the limits of grading while others extend beyond the property boundaries. A geotechnical summary including a description of each numbered landslide/landslide and the preliminary recommendations to mitigate the landslide is also presented on Table 1 (presented at the rear of the text). The landslide deposits include graben material (and associated colluvial soils), relatively undisturbed blocks of formational material and weathered formational material consisting of soils characteristic of the on-site bedrock units (i.e. silty sands and silty to sandy clays). Graben development at the head of the landslides appears to be moderate to relatively 4 -6- Leighton 971009-005 minor depending on the amount of movement of the landslide. The landslide material is generally moderately fractured and jointed at depth and highly weathered near the surface and at the toe of the landslides. The landslide basal mpture surfaces, as observed in the borings, typically consisted of a paper-thin to 1/4-inch thick remolded clay seams. In general, the landslide basal mpture surfaces appear to correspond to either an existing clay seam or a weak zone in the formational claystone. Several of the smaller landslides shown on the Geotechnical Map (Plate 1) are shallow surficial slumps/debris flow deposits (generally less than 5 to 15 feet thick). These shallow surficial slumps or debris flows appear to have developed as a result of prior landslide activation, seepage zones and/or oversteepened canyon side-walls within highly weathered portions of the formational soils. Due to potentially instability concems and compressible nature, the landslide deposits within the limits of the planned grading are considered unsuitable for structural support in their present condition and remedial measures (i.e. buttressing with fill and/or removals of the unstable and potentially compressible portions) will be required. Preliminary recommendations for the stabilization of the landslides are presented in Section 4.2, on Table 1, and indicated on the Remedial Grading Map (Plate 2). With regard to the ancient landslides, site development appears feasible from a geotechnical standpoint. However, Landslides Numbers 5, 9, 9A, and 12, all of which, extend off-site (or outside the proposed limits of grading).may require off-site grading in order to mitigate the landslide. 2.2.6 Santiago Formation (Map Symbol - Ts) The Tertiary-aged Santiago Formation, as encountered during our field investigation, consists primarily of massively bedded sandstones and claystones/siltstones. The siltstones and claystones generally are olive green to gray (unweathered), damp to moist, stiff to hard, moderately weathered, fractured and sheared. The sandstone generally consists of orange brown (iron oxidized staining) to light brown, damp to moist, dense to very dense, silty fine to medium grained sandstone. In previous reports this unit was classified and mapped as the Delmar Formation and Torrey Sandstone. Recent publications (including Tan and Kennedy, 1996) classify these units in north San Diego County as the Santiago Formation. When reviewing the boring and trench logs from previous investigations, this recent change should be taken into account. -7- Leighton 971009-005 2.3 Geologic Stmcture The general structure of the bedrock appears to be near horizontal. Based on the subsurface data, bedding within the Santiago Formation generally exhibits variable bedding with strikes ranging from northwest to northeast and dips typically 5 to 15 degrees to the southeast and northwest. Locally, cross bedding was observed with dips steeper than 15 degrees. Clay seams and/or landslide rupture surfaces encountered in the borings generally trend parallel to the bedding. Jointing on-site is very variable, but predominantly trends subparallel to the existing slopes. Jointing dips were found to be generally moderately to steeply dipping. Jointing was mainly encountered in the upper portion of the bedrock becoming less pronounced with depth. Randomly oriented shears were encountered mainly in the Santiago Formation claystone and siltstone. Numerous wide, diffuse zones of shearing, as well as more well-defined zones, were encountered in the bedrock, and are thought to be the result of regional tectonic shearing of the relatively stiff and unyielding siltstone and claystone. 2.4 Fauhing Our discussion of faults on the site is prefaced with a discussion of Califomia legislation and state policies conceming the classification and land-use criteria associated with faults. By definition of the Califomia Mining and Geology Board, an active fault is a fault that has had surface displacement within Holocene time (about the last 11,000 years). The State Geologist has defined a potentiallv active fault as any fault considered to have been active during Quatemary time (last 1,600,000 years) but that has not been proven to be active or inactive. This definition is used in delineating Fault-Rupture Hazard Zones as mandated by the Alquist-Priolo Earthquake Fault Zoning Act of 1972 and as most recently revised in 1997. The intent of this act is to assure that unwise urban development does not occur across the traces of active faults. Based on our review of the Fault-Rupture Hazard Zones, the site is not located within any Fault-Rupture Hazard Zone as created by the Alquist-Priolo Act (Hart, 1997). San Diego, like the rest of southem Califomia, is seismically active as a result of being located near the active margin between the North American and Pacific tectonic plates. The principal source of seismic activity is movement along the northwest-frending regional fault zones such as the San Andreas, San Jacinto and Elsinore Faults Zones, as well as along less active faults such as the Rose Canyon Fault Zone. Our review of geologic literature pertaining to the site ahd general vicinity indicates that there are no known major or active faults on or in the immediate vicinity of the site (Weber, 1982, and Jennings, 1994). Evidence for faulting was not encountered during our field investigation. The nearest known active fault is the Rose Canyon Fauk Zone, which is considered a Type B Seismic Source based on the 1997 Uniform building Code (UBC), and is located approximately 7.0 miles (11.2 kilometers) west of the site. Because of the lack of known active faults on the site, the potential for surface mpture at the site is considered low. Leighton 971009-005 2.5 Seismic Considerations The principal seismic considerations for most stmctures in southem Califomia are surface mpturing of fault traces and damage caused by ground shaking or seismically induced ground settlement. The possibility of damage due to ground mpture at the site is considered low since active faults are not known to cross the site. Hazards from seiches and tsunamis are not present as the site is located away from the immediate coastal area and there are no large standing bodies of water in or near the site. The seismic hazard most likely to impact the site is ground-shaking resulting from an earthquake on one of the major regional faults. The effects of seismic shaking can be reduced by adhering to the most recent edition of the Uniform Building Code and design parameters of the Stmctural Engineers Association of Califomia. 2.5.1 Liquefaction and Dvnamic Settlement Liquefaction and dynamic settlement of soils can be caused by strong vibratory motion due to earthquakes. Research and historical data indicate that loose granular soils underlain by a near-surface ground water table are most susceptible to liquefaction, while the stability of most silty clays and clays is not adversely affected by vibratory motion. Because of the dense nature of the underlying formational material and lack of a shallow permanent groundwater table, it is our opinion that the potential for liquefaction or seismically induced dynamic settlement across the majority of the site due to the design earthquake is low. However, relatively shallow groundwater and loose sandy soils are present in the main canyons and the potential for liquefaction of these in considered moderate unless provisions to mitigate the potential liquefaction are not performed during site grading. We anticipate that after the removal of the unsuitable material above the ground water table, placement of fill soils on the order of 15 to 20 feet above the current grades in these areas and consolidation of the saturated sandy soils occur (after the placement of the fill soils), the potential for surface manifestation of liquefaction in these areas will be low. 2.5.2 Uniform Building Code Seismic Parameters The site is located within Seismic Zone 4. The closest active fault is the Rose Canyon Fauh Zone, which is considered a Type B Seismic Source (per 1997 UBC criteria) and is located approximately 7.0 miles (11.2 kilometers) west of the site. The closest Type A Seismic Source is the Julian segment of the Elsinore Fault Zone, which is located approximately 23.5 miles (38 kilometers) east of the site. The soil profile type at the site, following the planned grading is anticipated to be Sc. Near source factors of Na = 1.0 and Nv= 1.0 are considered appropriate base on the seismic setting. -9- Leighton 971009-005 2.6 Ground Water Ground water was encountered in a number of the exploratory borings and trenches excavated across the site. Random seepage zones were also encountered in some of the exploratory borings and surface water was observed in the south flowing drainage on the west side of the site and in the large west flowing drainage (along proposed Poinsettia Lane) in the southernmost portion of the site. The approximate depths and elevations of the encountered ground water are depicted on the boring and trench logs (Appendix B). The ground water table encountered in the main drainages is generally perched ground water within the alluvial soils. The ground water that was encountered in the main canyons of the site at the time of our preliminary and supplemental investigations was approximately 5 to 20 feet below the existing ground surface. Ground water seepage zones in the on-site formational material was encountered at slightly elevated depths relative to the ground water depths in the adjacent drainages as the ground water table will generally follow the overlying topography, although with less relief Seasonal fluctuations of surface water and ground water should be expected. Subdrains are recommended in the canyon removal areas and the buttress and stability fills as indicated in Appendix D. The approximate location of recommended canyon subdrains are depicted on the Remedial Grading Map (Plate 2). Specific subdrain recommendations will be made when more detailed grading plans are developed. It should be noted that ground water levels might vary at the time of constmction from those elevations encountered during our preliminary and supplemental investigations. Since the elevations at which ground water was encountered were generally below anticipated finish grade elevations, it is our opinion that ground water related problems should be minimal provided the recommendations presented in this report are incorporated into the design and constmction of the project. It is our recommendation, however, that periodic inspection be made by either our soil engineer or engineering geologist during the grading operations and/or constmction for the presence of ground water. Remedial measures, if any, can be recommended on a case-by-case basis during the grading and construction operations. 2.7 Engineering Characteristics of On-site Soils Based on the results of our current geotechnical investigation, previous geotechnical investigations of the site (Appendix A), laboratory testing of representative on-site soils, and our professional experience on adjacent sites with similar soils, the engineering characteristics of the on-site soils are discussed below. 2.7.1 Expansion Potential The expansion potential of the on-site soils ranges from very low to very high. The sandstone within the Santiago Formation and sandy surficial soils are anticipated to be in the very low to moderate expansion range. The siltstone and claystone of the Santiago Formation, as well as the clayey topsoil, alluvium, and colluvium are anticipated to have a medium to very high expansion potential. Geotechnical observation and/or laboratory testing upon completion of the graded pads are recommended to determine the actual expansion potential of finish grade soils on the graded lots. To reduce the possibility of having expansion soils at or near finish pad grades, the clayey soils should be placed in deeper fill areas or outside the limits of the building pads. In addition, building pads 10- Leighton 971009-005 consisting of highly expansive soils may be overexcavated and replaced with fill soils having a lower expansion potential. 2.7.2 Soluble Sulfate Content Based on our professional experience on adjacent sites, the on-site soils should posses a negligible to moderate soluble sulfate content. However, some of the soils may possess a high sulfate content. Laboratory testing should be performed on the soils placed at or near finish grade after completion of site grading. 2.7.3 Excavation Characteristics With the exception of localized cemented zones within the Santiago Formation, it is anticipated that the on-site sedimentary and surficial soils may be excavated with conventional heavy-duty constmction equipment. Localized cemented zones may require heavy ripping. If a significant amount of oversize material (typically over 8 inches in maximum dimension) is generated, it should be placed to prevent possible settlement of the soil around the rocks, as recommended in Section 4.1 and Appendix D. 2.7.4 Earthwork Shrinkage and Bulking The volume change of excavated on-site materials upon recompaction as fill is expected to vary with materials and location. Typically, the surficial soils and bedrock materials vary significantly in natural and compacted density, and therefore, accurate earthwork shrinkage/bulking estimate cannot be determined. However, the following factors (based on the results of our subsurface investigations, laboratory tesfing, geotechnical analysis and professional experience on adjacent sites) are provided on Table 2 as guideline estimates. If possible, we suggest an area where site grades can be adjusted be provided as a balance area. Table 2 Earthwork Shrinkage and Bulking Estimates Geologic Unit Estimated Shrinkage/bulking Topsoil/Alluvium/Colluvium 5 to 15 percent shrinkage Landslide Deposits 0 to 10 percent shrinkage Santiago Formation 3 to 7 percent bulking'" * The clayey and more cemented sandy soils of the Santiago Formation are anticipated to bulk more than the slightly friable sands. il - Leighton 971009-005 2.8 Slope Stabilitv Our review of the 200-scale tentative tract map/grading plan (PDC, 2001b) indicates that the proposed cut and fill slopes on the site are proposed at a maximum inclination of 2:1 (horizontal to vertical) and up to approximately 50 and 70 feet in height, respectively. Our analysis indicates that the proposed fill slopes will have a deep-seated factor of safety of at least 1.5. With regard to natural slopes, our geotechnical analysis indicates the natural slopes should be grossly stable provided unforeseen geologic conditions are not present. However, our analysis indicates that some of the proposed cut slopes (especially cut slopes composed of claystones/siltstones ofthe Santiago Formation) may be surficially unstable and remedial measures such as the constmction of replacement'stability fills along the slope faces will be required. Slope stability analysis was also performed in areas underlain by landslides. Our analysis indicates that buttresses will be required in order to provide a minimum factor-of-safety of 1.5 or greater for slopes or grading pads proposed in areas of landslides. The recommended preliminary butfresses are presented on the Remedial Grading Map (Plate 2) and on the applicable Geologic Cross-Sections (Figures 2 through 14). It should be noted that additional analysis will be required after more detailed grading plans are developed. Specific preliminary recommendations conceming the stability of the slopes are presented in Section 4.2. 2.9 Settlement of Deep Fills Settlement of deep compacted fill soils occurs in two manners. One is short-term (elastic) settlement due to the weight of the overlying fill soils compressing the soil and driving the water out of the soil stmcture (consolidation). This typically occurs during or within a few months after the completion of grading. In general, silty to clayey soils will compress more slowly than sandy/granular soils. The second manner is long-term settlement, which typically occurs on the order of years after the fill soils are placed and is triggered by the additional wetting of the soils due to irrigation/precipitation. This occurs even to properly compacted fill soils and even though subdrains are installed. Silty to clayey soils typically settle as much as two times the amount that sandy soils will. Preliminary recommendations are presented in Sections 4.1.6 and 4.4. - 12- Leighton 971009-005 3.0 CONCLUSIONS Based on the results of our supplemental geotechnical investigation at the subject site and our review of the previous geotechnical reports applicable to the site (Appendix A), it is our professional opinion that the proposed mass grading of the Bressi Ranch property is feasible from a geotechnical standpoint, provided the following conclusions and recommendations are incorporated into the project plans, specifications, and followed during the site grading operations. The following is a summary of the geotechnical factors, which may effect development of the site. • Based on our subsurface exploration and review of pertinent geotechnical reports, the site is underlain by the Santiago Formation, landslide deposits, alluvium, colluvium, topsoil and documented and undocumented fill soils. • The undocumented fill, topsoil, colluvium, alluvium and weathered formational materials are considered unsuitable in their present state and will require removal and recompaction in areas of proposed development or fiiture fill. • Due to potentially instability concems and compressible nature, the landslide deposits within the limits of the planned grading are considered unsuitable for structural support in their present condition and remedial measures (i.e. buttressing with fill and/or removals of the unstable and potentially compressible portions) will be required. Preliminary recommendations for the stabilization of the landslides are presented in Section 4.2, on Table 1, and indicated on the Remedial Grading Map (Plate 2). • Siltstone and claystone soils of the Santiago Formation are highly to very highly expansive. These expansive soils should either be removed where present within 5 feet of finish pad grades and replaced with soil having a lower expansion potential or a special foundation design (i.e. post-tensioned design) should be provided. • The existing on-site soils appear to be suitable material for use as fill provided they are relatively free of rocks (larger than 8 inches in maximum dimension), organic material and debris. • Active faults are not known to exist on or in the immediate vicinity of the site. Because of the lack of known active faults on the site, the potential for surface mpture at the site is considered low. • The main seismic hazard that may affect the site is ground shaking from one of the active regional faults. • Evidence for faulting was not encountered during our field investigation. The nearest known active fault is the Rose Canyon Fault Zone, which is considered a Type B seismic source based on the 1997 Uniform building Code (UBC), and is located approximately 7.0 miles (11.2 kilometers) west of the site. • Due to the clayey and/or relatively dense nature of the on-site soils, the potential for liquefaction and dynamic settlement of the site is considered unlikely, provided the recommendations for site grading (as indicated in Section 4.1 and Appendix D) are adhered to. However, relatively shallow groundwater and loose sandy soils are present in the main canyons and the potential for liquefaction of these in 13- Leighton 971009-005 considered moderate unless provisions to mitigate the potential liquefaction are not performed during site grading. The ground water table was encountered in the on-site alluvium/colluvium at depths from approximately 5 to 20 feet below the existing ground surface of the main drainages. In general, the ground water table within the main canyon along proposed Poinsettia Lane is anticipated to be on the order of 5 to 10 feet in depth while the north-south trending canyons on the west and east sides are on the order to 10 to 20 feet in depth. Localized seeps were also observed in a number ofthe large-diameter borings at various elevations with the formational material. However, ground water on the site is not anticipated to be a significant factor during site grading and subsequent development. If ground water seepage conditions are encountered during site development, recommendations to mitigate the conditions can be made on a case-by-case basis at that time. The expansion potential of the on-site soils ranges from very low to very high. The sandstone within the Santiago Formation and sandy surficial soils are anticipated to be in the very low to moderate expansion range. The siltstone and claystone of the Santiago Formation, as well as the clayey topsoil, alluvium, and colluvium are anticipated to have a medium to very high expansion potential. Based on our professional experience on adjacent sites, the on-site soils should posses a negligible to moderate soluble sulfate content. However, some of the soils may possess a high sulfate content. With the exception of localized cemented zones within the Santiago Formation, it is anticipated that the on-site sedimentary and surficial soils may be excavated with conventional heavy-duty construction equipment. Localized cemented zones may require heavy ripping. All oversized material should be placed in accordance with the recommendations presented in Section 4.0 and Appendix D to minimize settlement of the material around the oversized rocks. In general, when recompacted as fill soils, the surficial units (including landslide deposits, topsoil, colluvium, alluvium, etc.) are anticipated to shrink and the bedrock materials are likely to bulk. It is anticipated that any planned major cut slopes that will be comprised of siltstones and/or claystones of the Santiago Formation will require stabilization measures to mitigate potential surficial instability. A detailed discussion on slope stability is provided in Section 4.2. Potential settlement of relatively deep fills is anticipated to mainly occur during or within a few months following the completion of grading. However, areas of deep fill should be monitored to ensure that the majority of the settlement occurs prior to construction of stmctures and other settlement sensitive improvements. In addition, lots underlain by fill differential thicknesses in excess of 20 feet will require the utilization of a special foundation design (i.e. a post-tensioned slab design). The potential for long term settlement of the alluvial materials within the main canyons, if not removed during grading, is potentially significant. 14- Leighton 971009-005 4.0 RECOMMENDATIONS 4.1 Earthwork We anticipate that earthwork during the mass grading operations at the site will consist of site preparation, removals of unsuitable soil, excavation of cut material, fill placement, and trench excavation and backfill. We recommend that earthwork on-site be performed in accordance with the following recommendations, the City of Carlsbad grading requirements, and the General Earthwork and Grading Specifications for Rough-Grading (GEGS) included in Appendix D. In case of conflict, the following recommendafions shall supersede those included as part of Appendix D. 4.1.1 Site Preparation Prior to the grading of areas to receive structural fill or engineered structures, the areas should be cleared of surface obstmctions, any existing debris, unsuitable material (such as desiccated documented fill soils, undocumented fill soils, topsoil, colluvium, alluvium, landslide deposits, and weathered formational materials) and stripped of vegetation. Vegetation and debris should be removed and properly disposed of off-site. Holes resuhing from the removal of buried obstmctions that extend below finished site grades should be replaced with suitable compacted fill material. Areas to receive fill and/or other surface improvements should be scarified to a minimum depth of 6 to 12 inches, brought to an above-optimum moisture condition, and recompacted to at least 90 percent relative compaction (based on American Standard of Testing and Materials [ASTM] Test Method D1557). 4.1.2 Removal and Recompaction of Unsuitable Soils As discussed in Sections 2.2 and 3.0, portions of the site are underlain by unsuitable soils, which may settle under the surcharge of fill and/or foundation loads. These materials include desiccated documented fill soils, undocumented fill soils, topsoil, colluvium, alluvium, landslide deposits and weathered formational material. Compressible materials not removed by the planned grading should be excavated to competent material, moisture conditioned or dried back (as needed) to obtain an above-optimum moisture content, and then recompacted prior to additional fill placement or surface improvements. The actual depth and extent of the required removals should be determined during grading operations by the geotechnical consultant; however, estimated removal depths are summarized below. 1) Existing Documented Fill The desiccated upper portion of the existing documented fills located in the eastem and southeastem portions of the site (associated with the grading of Carrillo Ranch) should be removed to competent fill prior to placement of additional fill. These materials can be utilized as fill materials provided they are moisture conditioned and free of deleterious materials. The estimated removal depths of the desiccated documented fills are anticipated to be on the order of 1 to 5 feet. However, deeper removals may be required along the edges of the fill where left-in-place unsuitable -15- Leighton 971009-005 soils may be present below the 1:1 (horizontal to vertical) removal edge extending from the existing toe-of-slope down undemeath the fill. 2) Existing Undocumented Fill The existing undocumented fills should be completely removed prior to placement of additional fill. These materials can be utilized as fill materials provided they are moisture conditioned and free of deleterious materials. The estimated removal depths of the undocumented fill soils range from 1 to more than 25 feet in depth. All trash, constmction debris, and decomposable material should be removed and disposed of off-site. 3) Topsoil Areas to receive fill which are on slopes flatter than 5:1 (horizontal to vertical) and where normal benching would not completely removed the topsoil, should be stripped to suitable formational material prior to fill placement. Topsoil is expected to be generally 1 to 4 feet thick, although localized deeper accumulations may be encountered during grading. 4) Alluvium and Colluvium In cut and fill areas, colluvial and alluvial materials should be completely removed to competent material. Where the alluvium/colluvium is located above the water table, this will most likely entail complete removal of these materials to competent bedrock. In areas where a shallow water table prevents the removal of these materials using conventional earthmoving equipment, (i.e. scrapers), we recommend the remaining material be removed by top loading (wet removal) or be surcharged and drained with wick drains. At the present time, we recommend fiirther investigation of the areas where shallow ground water is present within the alluvial soils in order to determine the compressibility characteristics of the alluvial soils. Based on the resuks of the addhional evaluation, specific geotechnical recommendations can be provided conceming the mitigation of the deep saturated alluvium and fill soils placed in these areas. 5) Landslide Deposits The landslide deposits within the limits of the planned grading should be removed to competent material during site grading in order to remove the highly disturbed and weathered material. The actual depth of stripping or overexcavation should be determined during grading based on field observations by the geotechnical consultant. However, preliminary recommendations relative to the removals of the landslides are presented on Table 1 for each of the mapped landslides on the site. Additional and/or specific recommendations may be made during the grading plan review after the completion of more detailed grading plans are developed. 16- Leighton 971009-005 4.1.3 Excavations Excavations of the on-site sedimentary and surficial materials may generally be accomplished with conventional heavy-duty earthwork equipment. Localized cemented zones in the Santiago Formation may be encountered that may require heavy ripping. All oversized rock that is encountered should be placed as fill in accordance with the recommendations presented Appendix D. 4.1.4 CutT'ill Transition Conditions In order to reduce the potential for differential settlement in areas of cut/fill transitions, we recommend the entire cut portion of the transkion building pads be overexcavated and replaced with properly compacted fill to mitigate the transkion condkion beneath the proposed stmcture. For transitions less steep than a 2:1 (horizontal to vertical), the overexcavation of the cut portion of the building pad should be a minimum of 4 feet below the planned finish grade elevation of the pad. For cut/fill transitions steeper than a 2:1 (horizontal to vertical) and for franskions beneath multi-unk and large commercial sfructures, site specific overexcavation recommendations should be made after the final grading and development plans are completed. All overexcavations should extend laterally at least 10 feet beyond the building perimeter or footprint. 4.1.5 Fill Placement and Compaction The on-site soils are generally suitable for use as compacted fill provided they are free of organic material, trash or debris, and rock fragments larger than 8 inches in maximum dimension. All fill soils should be brought to above-optimum moisture conditions and compacted in uniform lifts to at least 90 percent relative compaction based on the laboratory maximum dry density (ASTM Test Method D1557). The optimum lift thickness required to produce a uniformly compacted fill will depend on the type and size of compaction equipment used. In general, fill should be placed in lifts not exceeding 8 inches in compacted thickness. Placement and compaction of fill should be performed in general accordance with the current City of Carlsbad grading ordinances, sound constmction practices, and the General Earthwork and Grading Specifications of Rough-Grading presented in Appendix D. 4.1.6 Settlement of Deep Fills Subsequent to removals of compressible soils, fills of up to approximately 70 to 80 feet in thickness are planned on the site. Our experience and analysis indicates that potential settlement in these deep fill areas maybe on the order of 10 inches (depending on compactive effort) and may take as long as 6 months (or longer) to occur. Most of this settlement is anticipated to occur during grading. We anticipate that post constmction settlement of onsite fills to be on the order of a maximum of 3 inches. Release of building pad areas for constmction of stmctures in fill areas deeper than 50 feet should be made based on the resuks of surface settlement monuments placed at the completion of grading. -17. Leighton 971009-005 Provisional information indicates the release of building pads for constmction in areas not underlain by saturated alluvium will be on the order of 3 months following grading. 4.1.7 Expansive Soils and Selective Grading The laboratory test resuks and our professional experience with similar materials on sites in the vicinity indicate that the on-site soils possess a very low to very high expansion potential. As a result, the presence of highly expansive materials within 5 vertical feet from finish grade will require special foundation and slab considerations (i.e. the use of a post- tension foundation system). In general, this condkion should be limited to finish grade pads comprised of Santiago Formation claystone or siltstone (generally below an approximate elevation of 270 to 300 feet msl across the site) or where these materials are utilized as compacted fill within 5 feet of finish grade. As an altemative to the use of a post-tension foundation system on lots possessing a medium to very high expansion potential, the building pads may be overexcavated a minimum of 5 feet below finish pad grade and replace with properly compacted fill possessing very low to low expansion potential (i.e., the sandy soil of the Santiago Formation present in the higher elevations of the site. Should this altemative be chosen, the overexcavation should extend across the entire lot and be graded such that water does not accumulate beneath the stmctures (by providing a minimum 2 percent fall of the overexcavation bottom towards the street or existing fill). 4.2 Slope Stabilitv Review ofthe 200-scale tentative tract map/grading plans (PDC, 2001b), indicates that cut and fill slopes will be constmcted to maximum heights on the order of 50 and 70 feet, respectively. We understand that these finished slopes are planned at inclinations of 2:1 (horizontal to vertical) or flatter. Based on the resuks of our investigation and geologic interpretations, the proposed slopes were analyzed for gross stability utilizing the STABL slope stability program and surficial stability using the infinite slope equation with steady-state seepage. The parameters utilized in our slope stability analysis are based on our laboratory testing, our experience with similar soil types, and our professional judgment. The parameters utilized in the slope stability analysis are presented on Table 3. A summary of our slope stability analyses is presented below. Leighton 971009-005 Table 3 Slope Stability Soil Parameters Material Moist Unit Weight (pcf) Saturated Unit Weight (pcf) Friction Angle (degrees) Cohesion (psf) Artificial Fill Soils 125 130 25 200 Quatemary Alluvium 125 130 18 100 Landslide Material 125 130 18 100 Clay Seam/Rupture Surface 120 125 8 100 Santiago Formation (sandstone) 130 135 30 300 Santiago Formation (claystone along bedding) 130 135 13.5 100 Santiago Formation (claystone across bedding) 130 135 30 300 4.2.1 Deep-Seated Stabilitv 1) Fill Slopes The materials anticipated for use in fill slope grading will predominantly consist of sandy and silty to clayey soils of the Santiago Formation. Our analysis, assuming homogeneous slope conditions, indicates the anticipated fill slopes up to the maximum proposed heights of 70 feet will have a calculated factor of safety of 1.5 or greater with respect to potential, deep-seated failure. The proposed slopes should be consfructed in accordance with the recommendations of this report, the attached General Earthwork and Grading Specifications for Rough-grading (Appendix D), and City of Carlsbad grading code requirements. 2) Cut Slopes/Landslide Stabilization Engineering analysis of the proposed 2:1 (horizontal to vertical) cut slopes up to a maximum height of approximately 50 feet indicates the deep-seated stability of the slopes, in general, are stable from a geotechnical standpoint provided adverse geologic condkions are not present. The results of our stability analysis indicate that proposed cut slopes have a static factor of safety in excess of 1.5 for gross stability after remedial grading is performed (i.e. the constmction of butfresses) and our geotechnical recommendations are adhered to. 19-4 Leighton 971009-005 However, cut slopes consisting of Santiago Formation claystones and siltstones may be surficially unstable and may require the constmction of stability or replacement fills on the slopes. Based on our subsurface exploration (Appendix B), we anticipate that the majority of the cut slopes below an approximate elevation of 270 to 300 feet msl will consist of Santiago Formation claystones and sikstones. The stability fill keys should be constmcted a minimum of 15 feet wide, at least 5 feet below the toe-of- slope grade, and have a minimum 2 percent into-the-slope inclination. The approximate locations of the stability fill keys are presented on the Remedial Grading Map (Plate 2). A typical detail for stability fill constmction is provided in the attached General Earthwork and Grading Specifications (Appendix D). In addition. Geologic Cross-Sections A-A' through M-M' (Figures 4 through 17) were prepared in areas of landslides to further evaluate slope stability and to provide buttress designs, where appropriate, to increase the overall slope static factor-of-safety to at least a 1.5. Where buttresses are recommended, the preliminary dimensions are presented on the appropriate cross-section. A summary of the landslides is presented on Table 1. Prior to constmction of the recommended buttresses presented herein, the provisional stability recommendations should be reviewed and additional buttress design analysis performed based on the actual design grading plans. We recommend the geotechnical consultant document and geologically map all excavations including cut slopes during grading. The purpose of this mapping is to substantiate the geologic condkions assumed in our analyses. Addkional investigation and stability analysis may be required if unanticipated or adverse conditions are encountered during site development. 3) Slope Face Compaction and Finishing Due to the high expansion potential of the claystones and siltstones within the Santiago Formation, special compaction procedures will be necessary in order for the specified compaction to be achieved out to the slope face. Soils placed within 15 feet of the face of slope should consist of a mixture of clay and sand. The sole use of highly expansive clayey or clean sandy material within 15 feet of the face of slope should be avoided. Overbuilding the slope faces a minimum of 5 feet and frimming them back or frequent back-rolling with sheepsfoot compactors (at 1- to 3-foot vertical intervals) and back-rolling the completed slope with a short-shank sheepsfoot may be utilized to achieve the specified compaction of the slope face. 4) Stabilitv for Temporarv Backcut Slopes During Grading The temporary backcut slopes that will be created during removal of unsuitable materials or consfruction of the buttress and/or stabilization fills should have acceptable temporary factors of safety during grading. However, since there is still a small risk of slope instability, the possibility of temporary cut slopes failures may be reduced by: 1) keeping the time between cutting and filling operations to a minimum; 2) limiting the maximum length of back cut slopes exposed at any one time; 3) making removals at the head of the landslide before performing the buttress backcut near the toe of the landslide; and 4) cutting the temporary slopes at slope inclinations no steeper than 1-1/2:1 (horizontal to vertical) in locations of adverse geologic conditions -20- Leighton 971009-005 and 1:1 (horizontal to vertical) inclinations in other locations. In critical areas, we may recommend a contractor's representative observe the backcut for signs of instability during buttress constmction. Backcut safety is the responsibility of the contractor. It is of utmost importance to schedule the earthwork sequence such that the time between removal and recompaction is reduced to a minimum. Full-time geologic inspection should be performed during backcut excavation, not only to confirm the geologic conditions but also to provide early waming of incipient failure of the temporary excavations and to allow in-constmction reaction to accommodate such failures and keep their occurrence to a minimum. 4.2.2 Surficial Stabilitv Surficial stability of the 2:1 (or flatter) fill and cut slopes were evaluated during our supplemental investigation. Our calculations indicate a factor of safety in excess of 1.5 for surficial stability under 4-foot steady state seepage. However, due to the presence of potentially adverse geologic conditions, we have recommended stability fills along the slopes exposing Santiago Formation claystones or siltstones as discussed in Section 4.2.1, Part 2. 4.3 Control of Ground Water and Surface Waters Based on our preliminary and supplemental geotechnical investigations, it is our opinion that a permanent shallow ground water table does not currently exist at the site. However, a perched ground water condition is present within the alluvial soils in the main drainages of the property. The control of ground water in a hillside development is essential in order to reduce the potential for undesirable surface flow, hydrostatic pressure and the adverse effects of ground water on slope stability. We recommend that measures be taken to properly finish grade the ske such that drainage water is directed away from top-of-slopes and away from proposed stmctures. No ponding of water should be permitted. Drainage design is within the purview of the design civil engineer. Even with these provisions, our experience indicates that shallow ground water/perched ground water conditions can develop in areas where no such ground water conditions existed prior to site development, especially in areas where a substantial increase in surface water inflitration results from landscape irrigation. We recommend that an engineering geologist be present during grading operations to observe and record possible fiiture seepage areas and provide field recommendations for mitigation of future potential seepage. •21 Leighton 971009-005 4.3.1 Canyon Subdrains In order to help reduce the potential for ground water accumulation in the proposed fill areas, we recommend subdrains be installed in the bottoms of canyons fill areas (or on the sides of the removal if saturated alluvium is left-in-place) prior to fill placement. The canyon subdrains should consist of a 6-inch diameter PVC pipe surrounded by a minimum of 9-cubic feet (per linear foot) of 3/4-inch gravel wrapped in a filter fabric (Mirafi MON or equivalent). Where the subdrain is placed on fill in order to outlet the subdrain, the subdrain should consist of solid PVC pipe. The subdrain should have a minimum fall of at least 1 percent. Specific subdrain recommendations will be made upon our review of the final site grading plans. However, preliminary canyon subdrain locations are presented on the Remedial Grading Map (Plate 2). Details for subdrain constmction are provided in the attached General Earthwork and Grading Specifications (Appendix D). The actual need and/or location of canyon subdrains should be based on the evaluation of the configuration of the canyon bottoms by the geotechnical consultant after the removal of compressible soils have been completed. A representative of the project civil engineer should survey the installed subdrains for alignment and grade. Sufficient time should be allowed for the surveys prior to commencement of fill placement operations over the subdrain. The subdrain outlets should be installed to discharge water into poskive drainage devices (e.g. storm drain boxes, natural canyon bottoms, etc.). 4.3.2 Buttress and Stabilitv Fill Subdrains Subdrains should be provided in the buttress and stability fills constmcted on-site in order to minimize slope instability. The subdrains should be placed along the heel of the buttress or stability fill key (across the entire length of the key) and along the backcut at approximately 30-foot vertical intervals. The subdrains should be placed and constmcted in accordance with the recommendations presented in Appendix D. 4.3.3 Cut Slope Seepage Conditions Due to the anticipated presence of relatively permeable soils (i.e. Santiago Formation sandstone) underlain by relatively impermeable formational claystone or siltstones exposed in cut slopes on the site, groundwater seepage conditions are likely at these contacts. Slopes exposing these conditions (especially when the area at the top of the slope will be irrigated and/or where stmctures will be located at the toe-of-slope) should be evaluated by the geotechnical consultant to determine if some type of subdrain system should be placed to intercept the groundwater seepage. Recommendations to mitigate the seepage conditions include installing a toe-of-slope subdrain system, installing a subdrain system at or slightly below the contact between the permeable and impermeable materials or by replacing the slope with a stability fill (discussed in Section 4.2.1, Part 2). •22-4 Leighton 971009-005 4.4 Settlement Monitoring We recommend that fills greater than 50 feet in depth or where alluvium is left in place beneath the fill be monitored (by the placement of settlement monuments upon completion of rough-grading and periodic surveying). The number of settlement monuments necessary for monitoring and their placement locations should be determined following a review of the site grading plans by the project geotechnical consuhant. Constmction of settlement-sensitive stmctures in these deep fill areas should be postponed until anticipated settlement is within tolerable limks based on the analysis of the geotechnical consultant. 4.5 Surface Drainage and Lot Maintenance Positive drainage of surface water away from stmctures is very important. No water should be allowed to pond adjacent to buildings or the top of slopes. Poskive drainage may be accomplished by providing drainage away from buildings at a gradient of at least 2 percent for a distance of at least 5 feet, and further maintained by a swale of drainage path at a gradient of at least 1 percent. Where limited by 5-foot side yards, drainage should be directed away from foundations for a minimum of 3 feet and into a collective swale or pipe system. Where necessary, drainage paths may be shortened by use of area drains and collector pipes. Eave gutters also help reduce water inflitration into the subgrade soils if the downspouts are properly connected to appropriate outlets. Property owners should be reminded of the responsibiUties of hillside maintenance practices (i.e., the maintenance of proper lot drainage; the undertaking of property improvements in accordance with sound engineering practices; and the proper maintenance of vegetation, including pmdent lot and slope irrigation). 4.6 Graded Slopes It is recommended that all graded slopes within the development be planted with drought-tolerant ground cover vegetation as soon as practical to protect against erosion by reducing mnoff velocity. Deep-rooted vegetation should also be established to protect against surficial slumping. Oversteepening of existing slopes should be avoided during fine grading and constmction unless supported by appropriately designed retaining stmctures. We recommend terrace drains on the slopes be designed by the civil engineer and be constmcted in accordance wkh current City of Carlsbad specifications. Design of surface drainage provisions are within the purview of the project civil engineer. -23- Leighton 971009-005 4.7 Plan Review and Constmction Observation The provisional recommendations contained in this report must be confirmed once the actual grading plans are available. At that time, additional investigation and analysis maybe required. Construction observation of all on-site excavations and field density testing of all compacted fill should be performed by a representative of this office. We recommend that a geologist map all excavations during grading for the presence of potentially adverse geologic conditions. All footing excavations should be reviewed by this office prior to placing steel or concrete. •24- Leighton 971009-005 5.0 LIMITATIONS The conclusions and recommendations in this report are based in part upon data that were obtained from a limited number of observations, site visits, excavations, samples, and tests. Such information is by necessity incomplete. The nature of many sites is such that differing geotechnical or geological condkions can occur within small distances and under varying climatic conditions. Changes in subsurface condkions can and do occur over time. Therefore, the findings, conclusions, and recommendations presented in this report can be relied upon only if Leighton and Associates has the opportunity to observe the subsurface conditions during grading and construction of the project, in order to confirm that our preliminary findings are representative for the site. •25- Leighton Table 1 971009-005 Geotechnical Summarv of Existing Landslides Landslide Reference Number Location Geologic Conditions Conclusions and Recommendations 1 Eastem portion of PA-1 Landslide is a relatively large surficial slump. The landslide appears to have moved as a relatively incoherent mass of material. Failure was probably related to saturation conditions at the base of the weathered zone in the formational material (based on evidence of ground water seepage zones observed in the area). The backscarp was identified in Exploratory Trench T-27. The thickness of landshde is unknown, but anticipated to be on the order of 10 to 15 feet. A buttress approximately 60 feet wide with a depth ofat least 10 feet below the proposed toe-of-slope is recommended to remove the landsUde and stabilize the slope. A subdrain system at the heel of the key and panel drains in areas of observed and/or potential ground water seepage zones should also be anticipated. 2 Southeastem portion of PA-2 (Cross-Section E-E') Landslide is essentially the same as Landslide No. 1 (i.e. a relatively large surficial slump). The landslide appears to have moved as a relatively incoherent mass of material. Failure was probably related to saturation conditions of the weathered zone based on evidence of ground water seepage zones observed in the area. The basal slip surface was reportedly encountered in Exploratory Trench GT-42 at a depth of 8 feet below the ground surface. Complete removal of the relatively large surficial slump to competent formational material within the limits of grading is recommended. The removal depth is estimated to be on the order of 10 to 15 feet. In addition, it should be anticipated that the proposed fill slope near the bottom of the landslide will require a buttress approximately 40 feet wide with a depth of at least 15 feet below the proposed toe-of-slope. A subdrain system including possible panel drains in areas of observed and/or potential ground water seepage zones should be anticipated. 3 North central portion of OS-1 Landslide is a relatively large surficial slump. Landslide appears to have moved as a relatively incoherent mass of material. Failure was probably related to saturation conditions based on evidence of ground water seepage observed in the area. Thickness of landslide is unknown, but anticipated to be on the order of 10 to 15 feet. This landslide is outside the limits of the proposed grading; and therefore, no remedial grading is needed. However, we recommend that the fill slope key excavation for the proposed fill slope west of this landslide be geologically mapped to identify any evidence that the landslide may encroach into the fill slope key. Table 1 Geotechnical Summarv of Existing Landslides (continued) 971009-005 Landslide Reference Number Location Geologic Conditions Conclusions and Recommendations 4 Southeast side of OS-1 Landslide is a relatively large surficial slump. Landslide appears to have moved as a relatively incoherent mass of material. Failure was probably related to saturation conditions based on evidence of ground water seepage observed in the area. Thickness of landslide is unknown, but anticipated to be on the order of 10 to 20 feet. Complete removal of the relatively large surficial slump to competent formational material within the limits of grading is recommended. The removal depth is estimated to be on the order of 10 to 20 feet. In addition, it should be anticipated that the proposed fill slope above the landsUde on the east side will require a fiU slope/shear key approximately 15 feet wide with a depth ofat least 5 feet below the proposed toe-of-slope. 5 East side of OS-1 and West side of PA-10 Landslide is a relatively large surficial slump. Landslide appears to have moved as a relatively incoherent mass of material. Failure was probably related to saturation conditions based on evidence of ground water seepage observed in the area. Thickness of landshde is unknown, but anticipated to be on the order of 10 to 20 feet. Compiete removal of the relatively large surficial slump to competent formational material is recommended since the landsUde is completely within the limits of grading. The removal depth is estimated to be on the order of 10 to 20 feet. A subdram system including possible panel drains in areas of observed and/or potential ground water seepage zones may be needed. 6 Southwest side of PA-6 and northwest side of PA- IO (Cross-Section D-D') LandsUde complex is a relatively large and deep block- slide type landslide that may include more than one landslide mass. The landsUde complex appears to have moved as at least two semi-competent blocks along a north to northwest dipping rapture surface at an approximate elevation of 265 feet. Based on Borings LB-11 and LB-12, the upper approximately 25 feet of the landsUde mass was found to be potentially compressible and unsuitable for the support of fill or surface improvements. Remove the potentially compressible soil to competent landslide material in the upper portion of the landsUde. The removal depth is estimated to be on the order of 20 to 25 feet. The proposed in-filling of the canyon to the northwest with compacted fill will effectively buttress the landslide complex. Table 971009-005 Geotechnical Sununarv of Existing Landslides (continued) Landslide Reference Number Location Geologic Condkions Conclusions and Recommendations Northwestem portion of PA-11 (Cross-Section M-M') LandsUde is assumed to be a moderately sized rotational type landslide. The landslide appears to have moved as a relatively coherent mass of material. Thickness of landslide is unknown, but anticipated to be on the order of20 to 35 feet thick. Constraction of a buttress on the order of 50 feet wide with a depth of approximately 30 feet is recommended along the proposed toe of the fill slope to completely remove the landslide. A subdrain system in the buttress is also recommended. Westem portion of PA-11 Landslide is a moderately sized surficial slump. Landslide appears to have moved as a relatively coherent mass of material. Thickness of landslide is unknown, but anticipated to be on the order of 10 to 20 feet. Complete removal of the relatively large surficial slump to competent formational material within the limits of grading is reconmiended. The removal depth is estimated to be on the order of 10 to 20 feet The proposed fill slope on the west side of the landslide will require a fill slope/shear key approximately 15 feet wide and 5 feet deep below the toe-of-slope. Southem portion of PA-11 and partially offsite to the south (Cross-Section L-L') Landslide complex is a relatively large and deep block- slide type landsUde. The landslide likely failed along a clayseam or weak claystone bed at an elevation near the bottom of the adjacent drainage to the southeast. The landslide is estimated to be up to approximately 60 feet deep. It is not known how deep or the relative extent of the graben area, which will be located beneath a proposed fill slope. A second proposed fill slope is located near the bottom of the landslide just north of the property line. Some type of buttress will be required to stabilize the landslide and provide an adequate factor of safety for the proposed fill slopes. The estimated size of the buttress at the toe of the landslide is 100 feet wide and 15 feet deep at the toe. A stability fill/shear key is also recommended below the upper fill slope. This key should be a minimum of 15 feet wide and 10 feet deep below the proposed toe of slope. In addition, removal of the imsuitable and potentially compressible portion of the landslide is also recommended. The estimated depth of these removals is on the order of 10 to 20 feet within the limits of the proposed grading. Additional investigation and analvsis are recommended to better define the landshde geometrv and the butfress design. Table 1 Geotechnical Summary of Existing Landslides (continued) 971009-005 Landslide Reference Number Location Geologic Conditions Conclusions and Recommendations 9A Southern portion of PA-11 and partially offsite to the south (Cross-Section K-K') LandsUde complex is a relatively small block-slide type landslide. Based on Geocon Boring GLB-15 located offsite, the landslide failed along a clayseam within the Santiago Formation claystone at a depth of approximately 13 feet below the ground surface (at an approxunate elevation of 237 feet). The landslide is estimated to be up to approximately 25 to 30 feet deep. A fill slope is proposed on the upper portion of the landslide. A proposed cut slope on the off-site property will be made through the front of the landslide. Constraction of a butfress on the order of 60 feet wide with a depth of approximately 25 feet (or through the landslide rapture surface) is recommended along the proposed toe of the fiU slope located north of the property line. In addition removal of the upper approximately 5 to 10 feet of the landslide mass to competent material is also recommended. A subdrain system in the butfress is also recommended. 10 Southeastem comer of PA-11 (Cross-Section I-I') Landslide is a relatively small block-sUde type landslide. The landshde rapture surface was encountered in Boring LB-27 at an approximate depth of 16 feet below the ground surface (at an approximate elevation of 220 feet). It appears that the landsUde failed along a weak clay bed within the Santiago Formation claystone. The landslide is estimated to be up to approximately 25 to 30 feet deep. A fill slope is proposed on the lower portion of the landsUde north of the property line. Consfruction of a butfress on the order of 60 feet wide with a depth of approximately 10 feet (or through the landslide rapture surface) is recommended along the proposed toe of the fill slope located north of the property line. In addition removal of the upper approximately 5 to 10 feet of the landslide mass to competent material is also recommended. A subdrain system in the butfress is also recommended. 11 Southem portion of PA-8 and southeastem comer of PA-11 (Cross-Section H-H') Landslide is similar to Landslide No. 10 (i.e. a relatively small surficial slump). The landsUde rapture surface was encountered in Boring LB-26 at a depth of approximately 25 feet below the ground surface (at an approximate elevation of 220 feet). It appears that the landslide failed along a weak clay bed within the Santiago Formation claystone. The landslide is estimated to be up to approximately 25 to 30 feet deep. A proposed fill slope is proposed on the lower portion of the landslide north of the property line. Constraction of a butfress on the order of 60 feet wide with a depth of approximately 10 feet (or through the landslide rapture surface) is recommended along the proposed toe of the fill slope located north of the property line. In addition removal of the upper approximately 5 to 10 feet of the landslide mass to competent material is also recommended. A subdrain system in the butfress is also recommended. Table 1 Geotechnical Summary of Existing Landslides (continued) 971009-005 Landslide Reference Number Location Geologic Condkions Conclusions and Recommendations 12 Southem portion of PA-8, southeastem portion of PA-11, and westem portion of PA-12 (Cross-Sections C-C and G-G') Landslide is relatively large and extends partially off- site to the south. The landslide appears to have moved as a semi-competent block on a rapture surface that is dipping approximately 5 degrees to the southeast. The landslide is estimated to be up to approximately 30 to 50 feet deep. The lower end of the landslide is likely buried by recent alluvium/colluvium. Based on the current proposed grades of PA-12, the fill on and m front of the lower portion of the landshde effectively butfresses the landslide, and therefore, no butfress key is required. However, the unsuitable and potentially compressible portion of the landslide should be removed to competent material. Removal depths of the unsuitable material are estimated to be on the order of 20 to 30 feet deep. 13 Northwestem portion of PA-12 and the southem portion of OS-3 (Cross-Section F-F') Landslide is relatively large and extends partially into an open space area (OS-3). The landslide appears to have moved as a semi-competent block on a relatively flat rapture surface. The landslide rapture surface was encountered in Boring LB-7 at a depth of approximately 32.5 feet below the ground surface (at an approximate elevation of275 feet). It appears that the landslide foiled along a weak clay bed within the Santiago Formation claystone just above a sandstone unk. The landslide is estimated to be approximately 35 to 80 feet thick. Some type of butfress will be required to stabilize the landsUde. However, based on the current proposed grades, unknown geometry of the upper portion of the landslide, and our understanding that grading cannot occur within the open space area dictates that a butfress cannot be designed within the current parameters. An additional investigation and analvsis are recommended to better define the landslide geometrv and the butfress design and/or desien grades in front of the landslide 13 Northwestem portion of PA-12 and the southem portion of OS-3 (Cross-Section F-F') Landslide is relatively large and extends partially into an open space area (OS-3). The landslide appears to have moved as a semi-competent block on a relatively flat rapture surface. The landslide rapture surface was encountered in Boring LB-7 at a depth of approximately 32.5 feet below the ground surface (at an approximate elevation of275 feet). It appears that the landslide foiled along a weak clay bed within the Santiago Formation claystone just above a sandstone unk. The landslide is estimated to be approximately 35 to 80 feet thick. need to be raised in order stabilize the landsUde. 14 Southem portion of PA-13 Landslide is a relatively smaU block-slide type landslide. The landslide rapture surface is anticipated to be at the same approximate elevation as Landslide 15 (i.e. approximately 190 feet) within a clayey siltstone bed of the Santiago Formation. The landsUde is estimated to be up to approximately 25 to 30 feet deep. The lower end of the landslide is likely buried by recent alluvium/colluvium. Removal the potentially compressible soil to competent landsUde material in the upper portion of the landslide is recommended. The removal depth is estimated to be on fhe order of 10 to 15 feet. The proposed in-fiUmg of the canyon to the west will effectively butfress the landslide. In addition, it should be anticipated that the upper end of the landslide will need to be completely removed to competent formational material outside the proposed grading limits in order to stabilize the natural slope. A key approximately 15 feet wide should be constracted in this area. As an altemative, a building setback from the landsUde may be provided. Table 1 Geotechnical Summarv of Existing Landslides (continued) 971009-005 Landslide Reference Number Location Geologic Conditions Conclusions and Recommendations 15 Southem portion of PA-13 (Cross-Section J-J') Landslide is essentially the same as Landslide No. 14 (i.e. a relatively small block-slide type landslide). The landslide rapture surface was encountered in Boring LB-6 at an approximate depth of 26 feet below the ground surface (at an approximate elevation of 190 feet). It appears that the landslide failed along clayey siltstone bed directly below a cemented zone withm the Santiago Formation. The landslide is estimated to be up to approximately 25 to 30 feet deep. The lower end of tiie landslide is likely buried by recent alluvium/colluvium. Removal the potentially compressible soil to competent landslide material in the upper portion of the landslide is recommended. The removal depth is estimated to be on the order of 10 to 15 feet. The proposed in-filling of the canyon to the west with compacted fill will effectively butfress the landslide. In addition, it should be anticipated that the upper end of the landslide will need to be completely removed to competent formational material outside the proposed grading limits m order to stabilize the natural slope above the proposed relatively flat building pad. A key approximately 15 feet wide should be constracted in this area. 16 Northem portion of PA-13 Landslide is a relatively small block-slide type landslide. The landslide rapture surfece was encountered m Boring LB-14 at an approximate depth of 34 feet below the ground surfece (at an approximate elevation of 200 feet) near the top of a claystone bed within the Santiago Formation. The landslide is estimated to be up to approximately 35 to 40 feet deep. The lower end of the landslide is likely buried by recent alluvium/colluvium. Removal the potentially compressible soil to competent landsUde material in the upper portion of the landsUde is recommended. The removal depth is estimated to be on the order of 10 to 15 feet. The proposed in-filling of the canyon to the west with compacted fill will effectively butfress the landslide. 17 Northem portion of PA-13 LandsUde is essentially the same as Landslide No. 16 (i.e. a relatively small block-slide type landslide). The landslide rapture surface is anticipated to be at the same approximate elevation as Landslide 16 (i.e. approximately 200 feet) within a clayey siltstone bed of the Santiago Formation. The landslide is estimated to be up to approximately 25 to 30 feet deep. The lower end of the landslide is likely buried by recent alluvium/colluvium. Removal the potentially compressible soil to competent landslide material in the upper portion of the landslide is recommended. The removal depth is estimated to be on the order of 10 to 15 feet. The proposed in-fiUing of the canyon to the west with compacted fill will effectively buttress the landslide. Table 1 Geotechnical Sununarv of Existing Landslides (continued) 971009-005 Landslide Reference Number Location Geologic Conditions Conclusions and Recommendations 18 OS-3 and OS-7? And northwest portion of PA- 13 LandsUde is a moderately sized surficial slump. Landslide appears to have moved as a relatively coherent mass of material. Thickness of landslide is unknown, but anticipated to be on the order of 10 to 20 feet. Complete removal of the relatively large surficial slump to competent formational material within the limits of grading is recommended. A building setback may be required adjacent to the landsUde (due to the unstable landslide in the open space/natural slope above the building pad to the west). As an altemative, grading in the open space may be performed to stabilize the upper portion of the landslide outside the limits of grading. 19 OS-3 and OS-7? And northwest portion of PA- 13 (Cross-Section A-A') LandsUde is a moderately sized block-slide type landslide. The landslide appears to have moved as a semi-competent block on a rapture surface that is dipping approximately 10 to 12 degrees to the east. The landslide rapture surface was encoimtered in Boring LB-20 at an approximate depth of 18 feet below the ground surface (at an approximate elevation of 242 feet) within a weak claystone bed in the Santiago Formation. The landslide is estimated to be up to approximately 20 to 25 feet deep. The lower end of the landslide is Ukely buried by recent alluvium/colluvium. The proposed in-filling of the canyon to the west with compacted fill will effectively buttress the landslide. However, the landslide should be removed to competent formational material from a 1:1 projection down and away from the limits of fill. 20a and 20b OS-4 Landslide complex appears to be a relatively large block-slide type landslide completely located in an open space area. Since the landslide is completely within an open space area, no remedial grading is required. 21aand21b OS-4 LandsUde complex appears to be a relatively large block-slide type landslide completely located in an open space area. Since the landslide is completely within an open space area, no remedial grading is required. Table 1 Geotechnical Summarv of Existing Landslides (continued) 971009-005 Landslide Reference Number Location Geologic Conditions Conclusions and Recommendations 22 OS-4 Landslide complex appears to be a relatively large block-slide type landslide completely located in an open space area. Since the landslide is completely within an open space area, no remedial grading is required. 23 OS-2? Landslide is a small surficial slump. The landslide appears to have moved as a relatively incoherent mass of material. The thickness of the slide is unknown but believed to be on the order of 5 to 15 feet thick. Complete removal of the small surficial slump to competent formational material since the landslide is completely within the limits of grading. The removal depth is estimated to be on the order of 5 to 15 feet. 24 PA-3 Landslide is a small surficial slump in saturated colluvium behind an earthen embankment. Completely remove the small surficial slump along with the colluvium. Extend the canyon subdrain through this area. 971009-005 APPENDIXA References Blake, Thomas F., 1996, EQFAULT, Version 2.2. -, 1998, FRISKSP. Eisenberg, L.L, 1985, Pleistocene Faults and Marine Terraces, Northem San Diego County m Abbott, P.L., Editor, On the Manner of Deposition of the Eocene Strata in Northem San Diego County, San Diego Association of Geologists, Field Trip Guidebook, pp. 86-91. Eisenberg, L.L and Abbott, P.L., 1985, Eocene Lithofacies and Geologic History, Northem SanDiego County in Abbott, P.L., ed.. On the Manner of Deposition of the Eocene Strata in Northem San Diego County: San Diego Association of Geologists, Field Trip Guidebook, pp. 19-35. Geocon, Inc., 1982a, Soil and Geologic Reconnaissance, Bressi Ranch, San Diego County, Califomia, File No. D-2714-TOl, dated March 23,1982. , 1982b, Report of Phase I Geotechnical Study, Bressi Ranch, Carlsbad, Califomia, File No. D- 2714-T02, dated June 4, 1982. , 1992, PreliminaryGeotechnicalInvestigation, Rancho Carrillo, Villages E, J, and K, Carlsbad, Califomia, ProjectNo. 04787-12-04, dated December 30, 1992. , 1993, Geologic Investigation for Rancho Carrillo Project - Major Roads, Carlsbad, California, ProjectNo. 04787-12-01, dated January 15, 1993. , 1996, Geologic Investigation, Rancho Carrillo - El Fuerte Detention Basin Embankment and Existing Bressi Dam, Carlsbad, Califomia, Project No. 04787-12-11, dated November 25,1996. , 1998, Final Report of Testing and Observation Services During Site Grading, El Fuerte Detention Embankment, Rancho Carrillo, Carlsbad, California, ProjectNo. 05845-12-07, dated November 20, 1998. , 2000, Supplemental Soil and Geologic Investigation, Villages of La Costa - The Greens, Carlsbad, Califomia, ProjectNo. 06403-12-01, dated March 24, 2000. Hannan, D., 1975, Fauking in the Oceanside, Carlsbad and Vista Areas, Northem San Diego County, Califomia in Ross, A. and Dowlens, R.J., eds., Studies on the Geology of Camp Pendleton and Westem San Diego County, Califomia: San Diego Association of Geologists, pp. 56- 59. Hart, E.W., 1997, Fault-Rupture Hazard Zones in Califomia, Alquist-Priolo Special Studies Zones Act of 1972 with Index to Special Studies Zones Maps: Department of Conservation, Division of Mines and Geology, Special Publication 42. A- 971009-005 APPENDIX A (continued) Intemational Conference of Building Officials (ICBO), 1997, Uniform Building Code, Volume I - Administrative, Fire- and Life-Safety, and Field Inspection Provisions, Volume II - Stmctural Engineering Design Provisions, and Volume III - Material, Testing and Installation Provision, ICBO. Jennings, C.W., 1994, Fault Activity Map of Califomia and Adjacent Areas; Califomia Division of Mines and Geology, Geologic Data Map 6, Scale 1:750,000. Leighton and Associates, Inc., 1992, City of Carlsbad, Geotechnical Hazards Analysis and Mapping Study, 84 Sheets, dated November, 1992. , 1997, Preliminary Geotechnical Investigation, Bressi Ranch, Carlsbad, Califomia, Project No. 4971009-002, dated July 29,1997. , 1998,Recommendations for Overexcavation of Potentially Compressible Materials, for Onsite Portion of Land Outfall Sewer Relocation Project, Future Poinsettia Lane, Bressi Ranch, Carlsbad, Califomia, ProjectNo. 4971009-002, dated March 26, 1998. , 2000a, Geotechnical Review of Conceptual Grading Plans for the Wetland Restoration Area, Bressi Ranch, Carlsbad, Califomia, Project No. 4971009-005, dated January 25, 2000. , 2000a, Geotechnical Review of Land-Use Plans for Bressi Ranch, Carlsbad, Califomia, ProjectNo. 4971009-005, dated March 2,2000. , 2000c, Wetland Restoration Area Grading, Bressi Ranch, Carlsbad, Califomia, Project No. 4971009-005, dated April 17, 2000. , 2000d, Remedial Quantity Estimates, Offsite Portion of Proposed Poinsettia Lane, Bressi Ranch Development, Carlsbad, Califomia, ProjectNo. 971009-005, dated August 25,2000. , 2001, Geotechnical Feasibility Study, Offsite Poinsettia Lane, Alicante Road and Borrow Sites Within The Greens of The Villages of La Costa, Bressi Ranch Development, Carlsbad, Califomia, ProjectNo. 971009-005,dated January 5,2001. , Undated, Unpublished In-House Geotechnical Data. Lindvall, S.C, and Rockwell, T.K., 1995, Holocene Activity of the Rose Canyon Fauft Zone in San Diego, Califomia: Joumal of Geophysical Research, V. 100, No. B12, p. 24, 124-24,132. PDC, 2001 a, Cut/Fill Exhibit, 200 Scale, Bressi Ranch, Carlsbad, Califomia, dated February 14,2001. PDC, 2001b, Tentative Tract Map/Grading Plan, 200 Scale, Bressi Ranch, Carlsbad, Califomia, undated, received Febmary 16,2001. A-2 971009-005 APPENDIX A (continued) Reichle, M.S., and Kahle, J.E., 1990, Planning Scenario for a Major Earthquake, San Diego-Tijuana Metropolitan Area: Califomia Division of Mines and Geology, Special Publication 100 180 p. Rockwell, T.K., and Lindvall, S.C, 1990, Holocene Activity ofthe Rose Canyon Fauk in San Diego, Califomia, Based on Trench Exposures and Tectonic Geomorphology; Geological Society of America, Abstracts with Programs. , 1991, Minimum Holocene Slip Rate for the Rose Canyon Fauk in San Diego, Califomia m EnvironmentalPerils, San Diego Region: San Diego Association of Geologists, p. 37-46. Tan, S.S., and Kennedy, M.P., 1996, Geologic Maps of the Northwestem Part of San Diego County, Califomia: Califomia Division of Mines and Geology, DMG Open-File Report 96-02, 2 Plates. Tan, S.S., and Giffen, D.G., 1995, Landslide Hazards in the Northem Port ofthe San Diego Metropolitan Area, San Diego County, Califomia, Landslide Hazard Identification Map No. 35, Division of Mines and Geology, Open-File Report No. 95-04. Treiman, J.A., 1993, The Rose Canyon Fauk Zone, Southem Califomia: Califomia Division of Mines and Geology, Open-File Report 93-02,45 p. Seed, H.B., and Idriss, I.M., 1982, Ground Motions and Soil Liquefaction During Earthquakes, Monogram Series, Earthquake Engineering Research Institute, Berkeley, Califomia. Seed, H.B., Idriss, I.M., and Arango, I., 1983, Evaluation of Liquefaction Potential Using Field Performance Data, Joumal of Geotechnical Engineering: ASCE, Volume 109, March, pp. 458-482. Treiman, J.A., 1984, The Rose Canyon Fault Zone: A Review and Analysis, Califomia Division of Mmes and Geology, Funded by Federal Management Agency Cooperative Agreement EMF-83- K-0148. , 1993, The Rose Canyon Fault Zone, Southem Califomia: Califomia Division of Mines and Geology, Open-File Report 93-2,45p. Weber, F.H., 1982, Recent Slope Failures, Ancient Landslides and Related Geology ofthe Northem-Central Coastal Area, San Diego County, Califomia: Califomia Division of Mines and Geology, Open File Report 82-12LA, 77 p. Wilson, K.L., 1972, Eocene and Related Geology of a Portion of the San Luis Rey and Encinitas Quadrangles, San Diego County, Califomia: Master Thesis, University of Califomia at Riverside, 123 p. A-3 971009-005 APPENDIX A (contmued) Ziony, J.L, and Yerkes, R.F., 1985, Evaluating Earthquake and Surface-FaukingPotential in Ziony, ed., 1985, Evaluating Earthquake Hazards in the Los Angeles Region - An Earth - Science Perspective: U.S. Geological Survey, Professional Paper 1360, pp. 43-91. Aerial Photographs Date Source Flight Photo No(s) 4/11/53 USDA AXN-8M 19-21 A-4 971009-005 APPENDIX C Laboratorv Testing Procedures and Test Results Atterberg Limits: The Atterberg Limks were determined in accordance wkh ASTM Test Method D4318 for engineering classification of the fine-grained materials and presented in the table below: Sample Location Liquid Limk(%) Plastic Limk(%) Plastic Index(%) USCS Soil Classification B-2 #7 (§40' 35 16 19 CL B-3 #7 @30' 39 16 22 CL B-5 #6 @20' 42 20 22 CL B-6 #4(@15' 42 17 25 CL Direct Shear Tests: Direct shear tests were performed on selected remolded and/or undisturbed samples, which were soaked for a minimum of 24 hours under a surcharge equal to the applied normal force during testing. After transfer of the sample to the shear box and reloading of the sample, the pore pressures set up in the sample (due to the transfer) were allowed to dissipate for a period of approximately 1 hour prior to application of shearing force. The samples were tested under various normal loads utilizing a motor-driven, strain-confrolled, direct-shear testing apparatus at a strain rate of less than 0.001 to 0.5 inches per minute (depending upon the soil type). The test resuks are presented in the test data. Sample Location Sample Description Test Type Friction Angle (degrees) Apparent Cohesion (psf) LB-25 #3 (g 11- 14' Pale brown silty SAND Remolded to 90% 30 460 LB-25 #8 (g 53' Green gray CLAY Remolded to 90% 26 180 LB-26 #4 @ 20' Pale green sandy CLAY Undisturbed 25 750 LB-28 #1 (g 10' Pale yellow silty SAND Undisturbed 25 100 Moisture and Densitv Determination Tests: Moisture content and dry density determinations were performed on relatively undisturbed samples obtained from the test borings and/or trenches. The resuks of these tests are presented in the boring and/or trench logs. Where applicable, only moisture content was determined from "undisturbed" or disturbed samples. C-1 971009-005 APPENDIXC (Continued) Expansion Index Tests: The expansion potential of selected materials was evaluated by the Expansion Index Test, U.B.C. Standard No. 18-2 and/or ASTM Test Method 4829. Specimens are molded under a given compactive energy to approximately the optimum moisture content and approximately 50 percent saturation or approximately 90 percent relative compaction. The prepared 1-inch thick by 4-inch diameter specimens are loaded to an equivalent 144 psf surcharge and are inundated with tap water until volumetric equilibrium is reached. The results of these tests are presented in the table below: Sample Location Sample Description Compacted Dry Density (pcf) Expansion Index Expansion Potential Light brown clayey silty sand to sandy clay 101.5 28 Low Maximum Drv Densitv Tests: The maximum dry density and optimum moisture content of typical materials were determined in accordance with ASTM Test Method Dl 557. The results of these tests are presented in the table below: Sample Location Sample Description Maximum Dry Density (pcf) Optimum Moisture Content (%) LB-25 #3 (g 11-14' Pale brown silty SAND 117.5 13.5 LB-25 #8 @ 53' Green gray CLAY 111.0 17.5 Consolidation Tests: Consolidationtests were perfonned on selected, relatively undisturbed ring samples in accordance with Modified ASTM Test Method D2435. Samples were placed in a consolidometer and loads were applied in geometric progression. The percent consolidation for each load cycle was recorded as the ratio of the amount of vertical compression to the original 1 -inch height. The consolidation pressure curves are presented on the attached figures. Where applicable, time-rates of consolidation were recorded and presented below: Sample Location Coefficientof Consolidation C (cmVsec) B-2 (§20' 2.2x I0-' B-3 (§20' 2.3 X IQ-" B-5(§ 15' 2.9 x 10^ C-2 TERA TEST LABS, INC. DIRECT SHEAR TEST RESULT ASTM D 3080 Project Name: Project Number: Boring Number: Sample Number: Soil Description: BRESSI RANCH 971009-005 LB-25 3 PALE BROWN SILTY SAND (SM) Date Tested By Checked By Depth (ft.) 10/31/00 BCC 11.0-14.0 VERTICAL STRESS (psf) PROVING RING DIAL READING CONVERSI ON FACTOR SHEAR STRESS (psf) REUVXED STRESS (psO PEAK VERTICAL STRESS (psf) PROVING RING DIAL READING CONVERSI ON FACTOR SHEAR STRESS (psf) REUVXED STRESS (psO COHESION (psO 550 VERTICAL STRESS (psf) PROVING RING DIAL READING CONVERSI ON FACTOR SHEAR STRESS (psf) REUVXED STRESS (psO FRICTION (deg.) 35 PEAK RELAXED 554 51 44 15 765 660 REU \XED 1108 101 83 15 1515 1245 COHESION (pst) 460 2216 127 104 15 1905 1560 FRICTION (deg.) 30 TERATEST LABS, INC. DIRECT SHEAR TEST RESULT ASTM D 3080 Project Name: Project Number: Boring Number: Sample Number; Soil Description: BRESSI RANCH 971009-005 LB-25 6 GREENISH GRAY LEAN CLAY (CL) Date Tested By Checked By Depth (ft.) 10/31/00 BCC 53.0 VERTICAL STRESS (psf) PROVING RING DIAL READING CONVERSI ON FACTOR SHEAR STRESS (psf) RELAXED STRESS (psf) PEAK VERTICAL STRESS (psf) PROVING RING DIAL READING CONVERSI ON FACTOR SHEAR STRESS (psf) RELAXED STRESS (psf) COHESION (psf) 200 VERTICAL STRESS (psf) PROVING RING DIAL READING CONVERSI ON FACTOR SHEAR STRESS (psf) RELAXED STRESS (psf) FRICTION (deg.) 30 PEAK RELAXED 554 35 31 15 525 465 REU \XED 1108 54 45 15 810 675 COHESION (psf) 180 2216 99 86 15 1485 1290 FRICTION (deg.) 26 2500 2000 (A Q. 1500 1000 500 500 1000 1500 STRESS (psf) 2000 2500 TERATEST LABS, INC. DIRECT SHEAR TEST RESULT ASTM D 3080 Project Name: Project Number: Boring Number: Sample Number: Soil Description: BRESSI RANCH 971009-005 LB-26 4 PALE GREEN SANDY LEAN CLAY s(CL) Date Tested By Checked By Depth (ft.) 10/30/00 BCC 20.0 VERTICAL STRESS (psf) PROVING RING DIAL READING CONVERSI ON FACTOR SHEAR STRESS (psf) RELAXED STRESS (psf) PEAK VERTICAL STRESS (psf) PROVING RING DIAL READING CONVERSI ON FACTOR SHEAR STRESS (psf) RELAXED STRESS (psf) COHESION (psf) 750 VERTICAL STRESS (psf) PROVING RING DIAL READING CONVERSI ON FACTOR SHEAR STRESS (psf) RELAXED STRESS (psf) FRICTION (deg ) 29 PEAK RELAXED 554 77 74 15 1155 1110 RELAXED 1108 84 78 15 1260 1170 COHESION (psf) 750 2216 138 127 15 2070 1905 FRICTION (deg.) 25 9nnn 00 9nnn 00 9nnn 00 9nnn 00 9nnn - 00 9nnn - 00 9nnn 00 9nnn - 00 9nnn -1 00 9nnn 00 1 con 00 1 con 1 k 00 1 con w 00 1 con 00 1 con 00 1 con 00 1 con 00 1 con 00 1 con 00 1 con 00 STRAIN (psf) D C 00 STRAIN (psf) D C 00 STRAIN (psf) D C 00 STRAIN (psf) D C 00 STRAIN (psf) D C 00 STRAIN (psf) D C 00 STRAIN (psf) D C \ 00 STRAIN (psf) D C 00 STRAIN (psf) D C 00 STRAIN (psf) D C 00 00 00 00 00 00 00 00 00 00 00 n 00 n - 00 n - 00 n 00 n - 00 n - 00 n 00 n 00 n 00 n 00 U • ( ) 5C )0 10 00 15 STRESS (psf) 00 20 00 25 00 TIER A TEST LABS, INC. DIRECT SHEAR TEST RESULT ASTM D 3080 Project Name: Project Number: Boring Number: Sample Number; Soil Description; BRESSI RANCH 971009-005 LB-28 1 Date Tested By Checked By Depth (ft.) 10/30/00 BCC r 10 0 PALE YELLOW POORLY-GRADED SAND WITH SILT (SP-SM) VERTICAL STRESS (psf) PROVING RING DIAL READING CONVERSI ON FACTOR SHEAR STRESS (psf) RELAXED STRESS (psf) PEAK VERTICAL STRESS (psf) PROVING RING DIAL READING CONVERSI ON FACTOR SHEAR STRESS (psf) RELAXED STRESS (psf) COHESION (psf) 100 VERTICAL STRESS (psf) PROVING RING DIAL READING CONVERSI ON FACTOR SHEAR STRESS (psf) RELAXED STRESS (psf) FRICTION (deg.) 49 PEAK RELAXED 554 33 30 15 495 450 RELAXED 1108 103 98 15 1545 1470 COHESION (psf) 100 2216 160 147 15 2400 2205 FRICTION (deg.) 47 2500 2000 a z < I- 1500 1000 500 500 1000 1500 STRESS (psf) 2000 2500 Leightonand Associates,Inc. GENERAL EARTHWORK AND GRADING SPECIFICATIONS Page 1 of 6 LEIGHTON AND ASSOCIATES, INC. GENERAL EARTHWORK AND GRADING SPECIFICATIONSFOR ROUGH GRADING 1.0 General 1.1 Intent: These General Earthwork and Grading Specifications are for the grading and earthwork shown on the approved grading plan(s) and/or indicated in the geotechnical report(s). These Specifications are a part of the recommendations contained in the geotechnical report(s). In case of conflict, the specific recommendations in the geotechnical report shall supersede these more general Specifications. Observations ofthe earthwork by the project Geotechnical Consultant during the course of grading may result in new or revised recommendations that could supersede these specifications or the recommendations in the geotechnical report(s). 1.2 The Geotechnical Consultant of Record: Prior to commencement of work, the owner shall employ the Geotechnical Consultant of Record (Geotechnical Consultant). The Geotechnical Consultants shall be responsible for reviewing the approved geotechnical report(s)and accepting the adequacy of the preliminarygeotechnical findings, conclusions, and recommendationsprior to the commencementof the grading. Prior to commencement of grading, the Geotechnical Consultant shall review the "work plan" prepared by the Earthwork Contractor (Contractor) and schedule sufficient personnel to perform the appropriate level of observation, mapping, and compaction testing. During the grading and earthwork operations, the Geotechnical Consultant shall observe, map, and document the subsurface exposures to verify the geotechnical design assumptions. If the observed conditions are found to be significantly different than the interpreted assumptions during the design phase, the Geotechnical Consultant shall inform the owner, recommend appropriate changes in design to accommodate the observed condkions, and notify the review agency where required. Subsurface areas to be geotechnically observed, mapped, elevations recorded, and/or tested include natural ground after k has been cleared for receiving fill but before fill is placed, bottoms of all "remedial removal" areas, all key bottoms, and benches made on sloping ground to receive fill. The GeotechnicalConsultantshall observe the moisture-condkioningand processing of the subgrade and fill materials and perform relative compaction testing of fill to detennine the attained level of compaction. The Geotechnical Consultant shall provide the test results to the owner and the Contractor on a routine and frequent basis. 3030.1094 Leightonand Associates,Inc. GENERAL EARTHWORK AND GRADING SPECIFICATIONS Page 2 of 6 1,3 The Earthwork Confractor: The Earthwork Contractor (Contractor) shall be qualified, experienced, and knowledgeable in earthwork logistics, preparation and processing of ground to receive fill, moisture-condkioningand processing of fill, and compacting fill. The Contractor shall review and accept the plans, geotechnical report(s), and these Specifications prior to commencement of grading. The Contractor shall be solely responsible for performing the grading in accordance with the plans and specifications. The Contractor shall prepare and submit to the owner and the Geotechnical Consultant a work plan that indicates the sequence of earthwork grading, the number of "spreads" of work and the estimated quantities of daily earthwork contemplated for the site prior to commencement of grading. The Contractor shall inform the owner and the Geotechnical Consultant of changes in work schedules and updates to the work plan at least 24 hours in advance of such changes so that appropriate observations and tests can be planned and accomplished. The Contractor shall not assume that the Geotechnical Consultant is aware of all grading operations. The Contractor shall have the sole responsibilify to provide adequate equipment and methods to accomplish the earthwork in accordance with the appiicable grading codes and agency ordinances, these Specifications, and the recommendations in the approved geotechnical report(s) and grading plan(s). If, in the opinion of the Geotechnical Consultant, unsatisfactory condkions, such as unsuitable soil, improper moisture condition, inadequate compaction, insufficient buttress key size, adverse weather, etc., are resuhing in a qualify of work less than required in these specifications, the Geotechnical Consultant shall reject the work and may recommend to the owner that construction be stopped until the conditions are rectified. 2.0 Preparation of Areas to be Filled 2.1 Clearing and Gmbbing: Vegetation, such as bmsh, grass, roots, and other deleterious material shall be sufficiently removed and properly disposed of in a method acceptable to the owner, goveming agencies, and the Geotechnical Consultant. The Geotechnical Consultant shall evaluate the extent of these removals depending on specific site conditions. Earth fill material shall not contain more than 1 percent of organic materials (by volume). No fill lift shall contain more than 5 percent of organic matter. Nesting of the organic materials shall not be allowed. If potentially hazardous materials are encountered, the Contractor shall stop work in the affected area, and a hazardous material specialist shall be informed immediately for proper evaluation and handlingof these materials prior to continuingto work in that area. As presently defined by the State of Califomia, most refined petroleum products (gasoline, diesel fuel, motor oil, grease, coolant, etc.) have chemical constkuents that are considered to be hazardous waste. As such, the indiscriminate dumping or spillage of these fluids onto the ground may constitute a misdemeanor, punishable by fines and/or imprisonment, and shall not be allowed. 3030.1094 Leightonand Associates,Inc. GENERAL EARTHWORK AND GRADING SPECIFICATIONS Page 3 of 6 2.2 Processing: Existing ground that has been declared satisfactory for support of fill by the Geotechnical Consultant shall be scarified to a minimum depth of 6 inches. Existing ground that is not satisfactory shall be overexcavated as specified in the following section. Scarification shall continue until soils are broken down and free of large clay lumps or clods and the working surface is reasonably uniform, flat, and free of uneven features that would inhibk uniform compaction. 2.3 Overexcavation: In addition to removals and overexcavations recommended in the approved geotechnical report(s) and the grading plan, soft, loose, dry, saturated, spongy, organic-rich, highly fractured or otherwise unsuitable ground shall be overexcavated to competent ground as evaluated by the Geotechnical Consultant during grading. 2.4 Benching: Where fills are to be placed on ground with slopes steeper than 5:1 (horizontal to vertical units), the ground shall be stepped or benched. Please see the Standard Details for a graphic illustration. The lowest bench or key shall be a minimum of 15 feet wide and at least 2 feet deep, into competent material as evaluated by the Geotechnical Consultant. Other benches shall be excavated a minimum height of 4 feet into competent material or as otherwise recommended by the Geotechnical Consultant. Fill placed on ground sloping flatter than 5:1 shall also be benched or otherwise overexcavated to provide a flat subgrade forthefiU. 2.5 Evaluation/Acceptance of Fill Areas: All areas to receive fill, including removal and processed areas, key bottoms, and benches, shall be observed, mapped, elevations recorded, and/or tested prior to being accepted by the Geotechnical Consultant as suitable to receive fill. The Contractor shall obtain a written acceptance from the Geotechnical Consultant prior to fill placement. A licensed surveyor shall provide the survey control for determiningelevationsof processed areas, keys, and benches. 3.0 Fill Material 3.1 General: Material to be used as fill shall be essentially free of organic matter and other deleterious substances evaluated and accepted by the Geotechnical Consultant prior to placement. Soils of poor qualify, such as those with unacceptable gradation, high expansion potential, or low strength shall be placed in areas acceptable to the Geotechnical Consultantor mixed with other soils to achieve satisfactory fill material. 3.2 Oversize: Oversize material defined as rock, or other irreducible material with a maximum dimension greater than 8 inches, shall not be buried or placed in fill unless location, materials, and placement methods are specifically accepted by the Geotechnical Consultant. Placement operations shall be such that nesting of oversized material does not occur and such that oversize material is completely sunounded by compacted or densified fill. Oversize material shall not be placed within 10 vertical feet of finish grade or within 2 feet of future utilities or underground constmction. 3030.1094 Leightonand Associates,Inc. GENERAL EARTHWORK AND GRADING SPECIFICA'nONS Page 4 of 6 3.3 Import: If importing of fill material is required for grading, proposed import material shall meet the requirements of Section 3.1. The potential import source shall be given to the Geotechnical Consultant at least 48 hours (2 working days) before importing begins so that its suitabilify can be determined and appropriate tests performed. 4.0 Fill Placementand Compaction 4.1 Fill Layers: Approved fill material shall be placed in areas prepared to receive fill (per Section 3.0) in near-horizontal layers not exceeding 8 inches in loose thickness. The Geotechnical Consultant may accept thicker layers if testing indicates the grading procedures can adequately compact the thicker layers. Each layer shall be spread evenly and mixed thoroughly to attain relative uniformify of material and moisture throughout. 4.2 Fill Moisture Conditioning: Fill soils shall be watered, dried back, blended, and/or mixed, as necessary to attain a relatively uniform moisture content at or slightly over optimum. Maximum densify and optimum soil moisture content tests shall be performed in accordance with the American Sociefy of Testing and Materials (ASTM Test Method D1557-91). 4.3 Compaction of Fill: After each layer has been moisture-condkioned, mixed, and evenly spread, it shall be uniformly compacted to not less than 90 percentof maximum dry densify (ASTM Test Method D1557-91). Compaction equipment shall be adequately sized and be either specifically designed for soil compaction or of proven reliabilify to efficiently achieve the specified level of compaction with uniformify. 4.4 Compaction of Fill Slopes: In addition to normal compaction procedures specified above, compaction of slopes shall be accomplished by backrolling of slopes with sheepsfoot rollers at increments of 3 to 4 feet in fill elevation, or by other methods producing satisfactory results acceptable to the Geotechnical Consultant. Upon completion of grading, relative compaction of the fill, out to the slope face, shall be at least 90 percent of maximum densify per ASTM Test Method D1557-91. 4.5 Compaction Testing: Field tests for moisture content and relative compaction of the fill soils shall be performed by the Geotechnical Consultant. Location and frequency of tests shall be at the Consultant's discretion based on field conditions encountered. Compaction test locations will not necessarily be selected on a random basis. Test locations shall be selected to verify adequacy of compaction levels in areas that are judged to be prone to inadequate compaction (such as close to slope faces and atthe fill/bedrock benches). 3030.1094 Leightonand Associates,Inc. GENERAL EARTHWORK AND GRADING SPECIFICATIONS Page 5 of 6 4.6 Frequencv of CompactionTesting: Tests shall be taken at intervals not exceeding 2 feet in vertical rise and/or 1,000 cubic yards of compacted fill soils embankment. In addition, as a guideline, at least one test shall be taken on slope faces for each 5,000 square feet of slope face and/or each 10 feet of vertical height of slope. The Contractor shall assure that fill construction is such that the testing schedule can be accomplished by the Geotechnical Consultant. The Contractor shall stop or slow down the earthwork construction if these minimum standards are not met. 4.7 Compaction Test Locations: The GeotechnicalConsultantshall document the approximate elevation and horizontal coordinates of each test location. The Contractor shall coordinate with the project surveyor to assure that sufficient grade stakes are established so that the Geotechnical Consultant can determine the test locations with sufficient accuracy. At a minimum, two grade stakes within a horizontal distance of 100 feet and vertically less than 5 feet apart from potential test locations shall be provided. 5.0 Subdrain Installation Subdrain systems shall be installed in accordance with the approved geotechnical report(s), the grading plan, and the Standard Details. The Geotechnical Consultant may recommend addkional subdrains and/or changes in subdrain extent, location, grade, or material depending on conditions encountered during grading. All subdrains shall be surveyed by a land surveyor/civil engineer for line and grade after installation and prior to burial. Sufficient time should be allowed by the Contractor for these surveys. 6.0 Excavation Excavations, as well as over-excavation for remedial purposes, shall be evaluated by the Geotechnical Consultant during grading. Remedial removal depths shown on geotechnical plans are estimates only. The actual extent of removal shall be detennined by the Geotechnical Consultant based on the field evaluation of exposed conditions during grading. Where fill-over-cut slopes are to be graded, the cut portion of the slope shall be made, evaluated, and accepted by the Geotechnical Consultant prior to placement of materials for construction of the fill portion of the slope, unless otherwise recommended by the Geotechnical Consultant. 3030.1094 Leightonand Associates,Inc. GENERAL EARTHWORK AND GRADING SPECIFICATIONS Page 6 of 6 7.0 Trench Backfills 7.1 The Contractor shall follow all OHSA and Cal/OSHA requirements for safefy of trench excavations. 7.2 All bedding and backfill of utilify trenches shall be done in accordance with the applicable provisions of Standard Specifications of Public Works Construction. Bedding material shall have a Sand Equivalent greater than 30 (SE>30). The bedding shall be placed to 1 foot over the top of the conduk and densified by jetting. Backflll shall be placed and densified to a minimum of 90 percent of maximum from 1 foot above the top of the conduit to the surface. 7.3 The jetting of the bedding around the conduits shall be observed by the Geotechnical Consultant. 7.4 The Geotechnical Consultant shall test the trench backfill for relative compaction. At least one test should be made for every 300 feet of trench and 2 feet of fill. 7.5 Lift thickness of trench backfill shall not exceed those allowed in the Standard Specifications of Public Works Construction unless the Contractor can demonstrate to the Geotechnical Consultant that the fill lift can be compacted to the minimum relative compaction by his altemative equipment and method. 3030.1094 PROJECTED PtANE 1 TOI MAXIMUM FROM TOE OF StOPE TO APPROVED OnOUNO NATURAL OROUND FILL SLOPE REMOVE UNSUfTABLE MATERiAL r MIN.- KEY DEPTH ri3% MIN.—" U—18' MIN. LOWEST BENCH (KEY) BENCH HEIOHT NATURAL QROUND IMPACTED— A'VfPiCAL FILL-OVER-CUT SLOPE BENCH HEKJHT •IP MIN.—H LOWESTBENCHI I— 2' MIN. KEY DEPTH REMOVE UNSUITABLE MATERtAL CUT FACE SHAa BE CONSTRUCTB} PRIOR TO FNJL PlACEMBfT TO ASSURE ADEQUATE QEOLOQIC CONOmONS CUT FACE TO BE CONSTRUCTED PWOfl TO F«l. PLACaitENTv NATURAL OROUND OVERBUILT ANO TRIM BACK PROJECTEO PLANE 1 TOI MAXIMUM FROM TOE OF SLOPE TO APPROVEO OROUND^ DESION SLOPE REMOVE NSUTTABLE MATERIAL CUT-OVER-FILL SLOPE For Subdrains See Standard Detail C •"^—irt^tJ 4'TYPKya. 2' MIN. KEY DEPTH Mir BENCH BENCH HEIGHT — ILOWEST BENCH! SaCHINQ SHAa BE DONE WHEN SLOPES ANOLE IS EQUAL TO OR QREATER THAN 5:1 MMMUM BBCH HE»HT SHAU BE 4 FEET MMIMUM Fm. WIDTH SHALL BE 9 FEET KEYING AND BENCHING GENERAL EARTHWORK AND GRADING SPECIFICATIONS STANDARD DETAILS A REV.4/11/B6 FINISH GRADE SLOPE FACE -10' MIN.inr-^.COMPACTED FILL_-_-z: — OVERSIZE — WINDROW JETTED OR FLOODED GRANULAR MATERIAL • Oversize rock is larger than 8 Inches in largest dimension. • Excavate a trench In the compacted fill deep enough to bury all the rock. • Backfill With granular soil jetted or fkxxjed in piace to fill all the vokjs. • Do not iHJry rock within 10 feet of finish grade. • Windrow of txiried rock shaH be parallel to the finished skspe fill. ELEVATION A-A' PROFILE ALONG WINDROW A- JETTED OR FLOODED GRANULAR MATERIAL OVERSIZE ROCK DISPOSAL GENERAL EARTHWORK AND GRADINQ SPECIFICATIONS STANDARD DETAILS B 4/95 NATURAL GROUND BENCHING REMOVE UNSUITABLE MATERIAL 2- MIN. OVERLAP FROM THE TOP HOG RING TIED EVERY 6 FEET CALTRANS CLASS II PERMEABLE OR #2 ROCK' (9FT.'/FT.) WRAPPED IN FILTER FABRIC FILTER FABRIC (MIRAFI140ORv \ / APPROVED \C0LLECT0R PIPE SHALL CANYON SUBDRAIN OUTLET DETAIL PERFORATED PIPE 6-<|> MIN. APPROVED EQUIVALENT) BE MINIMUM 6" DIAMETER SCHEDULE 40 PVC PERFORATED PIPE. SEE STANDARD DETAIL D FOR PIPE SPECIFICATION DESIGN FINISHED GRADE NON-PERFORATED 6> MIN. FILTER FABRIC (MIRAFI 140 OR APPROVED EQUIVALENT) #2 ROCK WRAPPED IN FILTER FABRIC OR CALTRANS CLASS II PERMEABLE. CANYON SUBDRAINS GENERAL EARTHWORK AND GRADING SPECIFICATIONS STANDARD DETAILS C 4196 OUTLET PIPES 4'(j> NON-PERFORATED PIPE, 100' MAX, O.C. HORIZONTALLY, 30' MAX. O.C. VERTICALLY 15' MIN. : ^ BACKCUT 1:1 OR FLATTER 2' MIN POSITIVE SEAL SHOULD BE PROVIDED AT THE JOI OUTLET PIPE (NON-PERFORATED) CALTRANS CLASS II PERMEABLE OR #2 ROCK (3FT.'/FT.) WRAPPED IN FILTER FABRIC 12" MIN. OVERLAP FROM THE TOP HOG RING TIED EVERY 6 FEET \ FILTER FABRIC (MIRAFI 140 OR APPROVED EQUIVALENT) / T-CONNECTION FOR COLLECTOR PIPE TO OUTLET PIPE SUBDRAIN INSTALLATION - Subdrain collector pipe shall be Installed with perforattons down or, unless othenwise designated by the geotechnfcal consultanL Outlet pipes shafl be non-perforated pipe. The subdrain pipe shall have at least 8 perforattons unifomily spaced per foot Perforatkxi shall be y/ to W If drilled holes are used. All subdrain pipes shall have a gradient at least 2% towards the outlet SUBDRAIN PIPE - Subdrain pipe shall be ASTM D2751, SDR 23.5 or ASTM D1527, Schedule 40. or ASTM D3034, SDR 23.5, Schedule 40 Polyvinyl Chtoride Plastfc (PVC) pipe. All outlet pipe shall be placed In a trench no wkJer than twfce the subdrain pipe. Pipe shall be in soii of SE>30 jetted or flooded In place except for the outside 5 feot whfch shali be native soli backflll. BUTTRESS OR REPLACEMENT FILL SUBDRAINS GENERAL EARTHWORK AND GRADING SPECIFICATIONS STANDARD DETAILS D 4/95