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HomeMy WebLinkAbout58-9911063J.00; Carlsbad Research Center Lot 12; Carlsbad Research Center Lot 12; 1999-08-02E UPDATE REPORT C c c c c c c [ [ c c UPDATE GEOTECHNICAL INVESTIGATION CARLSBAD RESEARCH CENTER LOT 12 CARLSBAD, CALIFORNIA Prepared for Mr. Frank Sciacca DSK Carlsbad Partners, L.L.C. c/o Sciacca Development Company P.O. Box 2156 Rancho Santa Fe, CA 92067 URSGWC Project No. 58-9911063J.OO-UD001 August 2, 1999 US 6roilier woodward Clyde 1615 Murray Canyon Road, Suite 1000 San Diego, CA 92108-4314 619-294-9400 Fax: 619-293-7920 [ UPDATE REPORT UPDATE GEOTECHNICAL INVESTIGATION CARLSBAD RESEARCH CENTER LOT 12 CARLSBAD, CALIFORNIA Prepared for Mr. Frank Sciacca DSK Carlsbad Partners, L.L.C. c/o Sciacca Development Company P.O. Box 2156 Rancho Santa Fe, CA 92067 URSGWC Project No. 58-9911063J.OO-UD001 August 2, 1999 1/ffS Greiner Wo a a war a Clyde 1615 Murray Canyon Road, Suite 1000 San Diego, CA 92108-4314 619-294-9400 Fax: 619-293-7920 URS Greiner Woodward Clyde A Division of URS Corporation August!, 1999 1615 Murray Canyon Road, Suite 1000 San Diego, CA 92108 Tel: 619.294.9400 Fax: 619.293.7920 Offices Worldwide Mr. Frank Sciacca DSK Carlsbad Partners, L.L.C. c/o Sciacca Development Company P.O. Box 2156 Rancho Santa Fe, CA 92067 Subject: Update Geotechnical Investigation Carlsbad Research Center - Lot 12 Carlsbad, California URSGWC Project No, 58-9911063J.OO-UD001 Dear Mr. Sciacca: URS Greiner Woodward Clyde (URSGWC) is pleased to present the accompanying update report, which presents the results of our geotechnical investigation for the subject project. This study was performed in accordance with our proposal, dated July 7, 1999, and your authorization of July 11, 1999. This report presents our conclusions and recommendations pertaining to the geotechnical aspects of the proposed project. The results of our investigation indicate that the site is generally suitable for the proposed construction. If you have any questions or if we can be of further service, please give us a call. Very truly yours, URS GREINER WOODWARD CLYDE Ronald S. Johnson, G.$. $356 Project Manager RSJ:mjr Attachments Jteven M. Fitzwilliam, R.C. Project Engineer W:\9911063J\UD001-B.LDOC\30-JUL-99\SDG TABLE OF CONTENTS Section 1 Introduction 1-1 1.1 Purpose and Scope of Investigation 1-1 Section 2 Site Reconnaissance 2-1 2.1 Site Reconnaissance 2-1 Sections Site Conditions 3-1 3.1 Geologic and Seismic Setting 3-1 3.2 Site Development History 3-1 3.3 Surface Conditions 3-2 3.4 Subsurface Conditions 3-2 3.5 Groundwater 3-2 Section 4 Discussions, Conclusions and Recommendations 4-1 4.1 Geologic and Seismic Hazards 4-1 4.2 Site Earthwork 4-1 4.2.1 Soil Characteristics 4-1 4.2.2 Site Preparation 4-1 4.3 Surface Drainage 4-3 4.4 Subsurface Drainage 4-3 4.5 Foundations 4-3 4.6 Seismic Coefficient 4-4 4.7 Subterranean Walls 4-4 4.8 Slabs-on-Grade 4-5 4.9 Pavements 4-5 4.10 Corrosion Potential 4-6 Section 5 Uncertainty and Limitations 5-1 Figure Figure 1 Figure 2 Vicinity Map Site Plan URSGrelnerWoodwartCMe W:\9911063J\UD001-B.R.DOC\30-Jul-99\SDG SECTIONONE Introduction This report presents the results of URS Greiner Woodward Clyde's (URSGWC) update geotechnical investigation for the Carlsbad Research Center. The project is located east of El Camino Real and north of Palomar Airport Road in Carlsbad, California. The location of the project is shown on the Vicinity Map (Figure 1). For our study we have discussed the project with you and with Mr. Mike Woomer of Smith Consulting Architects, the project architects. We have also review the following reports and plans prepared by our firm and others pertaining to Lot 12 of the Carlsbad Research Center development: • "Preliminary Soil and Geologic Investigation, Carlsbad Research Center, Carlsbad, California," prepared by Woodward-Clyde Consultants, dated April 27, 1981. • "Additional Studies, Carlsbad Research Center, Phase I, Carlsbad, California," prepared by Woodward-Clyde Consultants, dated August 27, 1981. • "Addendum to Additional Studies, Carlsbad Research Center, Phase I, Carlsbad, California," prepared by Woodward-Clyde Consultants, dated September 3, 1981. • "As-graded Geotechnical Report, Rough Grading Completed, Carlsbad Research Center, Phase I, Carlsbad Tract No. 81-10, Carlsbad, California," prepared by San Diego Soils Engineering, Inc., dated April 21, 1982. • "Geotechnical Investigation, Callaway Golf Distribution Building, Carlsbad Research Center - Lot 12, Carlsbad, California," prepared by Woodward-Clyde Consultants, dated August 8, 1994. We understand that the proposed project will include five one-story buildings, four two-story buildings, asphalt parking, and landscaping. We understand the proposed buildings will be of concrete tilt-up construction supported on shallow foundations. We anticipate that the project will entail minor site earthwork and grading. This report presents our conclusions and recommendations pertaining to the project and has been prepared exclusively for DSK Carlsbad Partners, L.L.C. and their consultants in planning and design. Some of the recommendations included in this report have been previously transmitted to the project architect and structural engineer. 1.1 PURPOSE AND SCOPE OF INVESTIGATION The purpose of the geotechnical investigation is to evaluate the surface and subsurface conditions at the site and to provide geotechnical recommendations to assist the design team in project design. The scope of the investigation included a review of previous geotechnical investigations, a site reconnaissance, engineering evaluations and analyses, and preparation of this report suitable for submittal to the City of San Diego for permitting purposes. The geotechnical investigation was designed to develop conclusions and recommendations regarding the following: • Geologic and seismic setting of the site. • General site surface and subsurface conditions. W:\9911063J\UD001-B.R.DOC\30-Jul-99\SDG 1 - SECTIONONE Introduction Recommendations for site earthwork, including subgrade preparation. Appropriate foundation systems for the planned structures, given the subsurface conditions, seismic hazards, and anticipated loading conditions. Allowable bearing pressures and available lateral resistance (passive and frictional resistance) for shallow foundations. Estimated total and differential foundation settlements. Recommendations for design of slab-on-grade floors and asphalt pavements. Recommendations for seismic site coefficients based on the 1997 Unified Building Code. URSGrelner Woodward CWe W:\9911063J\UD001-B.R.DOC\30-Jul-99\SDG 1-2 SECTIONTWO Site Reconnaissance 2.1 SITE RECONNAISSANCE An engineer from our firm performed a site reconnaissance on July 15, 1999. The existing conditions and site access were evaluated and noted. The site reconnaissance was performed to verify that the field conditions were similar to those at the time of our last geotechnical investigation at the site in terms of site conditions, elevation, and surface characteristics. Photographs depicting the general site conditions were collected during the reconnaissance. W:\9911063J\UD001-B.R. DOC\30-Jul-99\SDG 2-1 SECTIONTHREE Site Conditions Our knowledge of the site conditions has been developed from a review of the area geology, historical information, previous investigations, and our site reconnaissance. 3.1 GEOLOGIC AND SEISMIC SETTING The site lies within the coastal margins along the western flanks of the Peninsular Range Province of southern California. The Peninsular Range Province is a well defined geologic and physiographic province southeastward from southern California to the tip of Baja California. The coastal subprovince consists of gently westward sloping Cetaceous through Quaternary age sedimentary formations that abut Jurassic age metamorphic and Cretaceous age crystalline rock to the east. The site is approximately 1A mile north of McClellan Palomar Airport and four miles east of the Pacific Ocean shoreline. The site is underlain by fill soil and formational soil of the Santiago and Point Loma Formations. The fill soil is generally derived from the on-site formational soil. The Rose Canyon-Offshore Zone of Deformation-Newport Inglewood fault zone contains the nearest active faults to the site. This zone of faults is located west of the site at a distance of approximately 7 miles (11 kilometers). Other active faults in Southern California include the Elsinore fault zone approximately 25 miles (40 kilometers)to the east and the Coronado Banks fault zones approximately 26 miles (42 kilometers) to the west. The "City of San Diego, Seismic Safety Study, Geologic Hazards and Faults," dated 1995 does not indicate the presence of any faults at the building site. 3.2 SITE DEVELOPMENT HISTORY The original geotechnical investigation at the site was performed by Woodward-Clyde Consultants for the entire Carlsbad Research Center and is discussed in our April 27, 1981 report. At the time of that investigation, the undisturbed terrain was part of a natural terrace surface that was part of an agricultural area. Several exploratory test pits were performed in the site vicinity during our 1981 study. Based on our review of our project files, we understand that the site was initially mass graded in 1981 as part of Phase I grading for the Carlsbad Research Center. Testing and observation services during this grading period were provided by San Diego Soils Engineering, Inc. and are summarized in their April 21, 1982 report. According to this repot, grading within the current site vicinity included removal of loose topsoil and residual soil, placement and compaction of fill soil to design grades, and performance of field and laboratory tests to determine the relative compaction and moisture content of compacted fill. Up to about 16 feet of compacted fill was place on Lot 12 during grading. At the completion of this phase of grading, the surface elevation of the graded portion of Lot 12 ranged from approximately +309 to +322 feet Mean Sea Level (MSL). In 1994 URSGWC (formerly Woodward-Clyde Consultants) performed a geotechnical of the subject site. The results of that investigation are presented in our report dated August 8, 1994. Six exploratory borings were performed for at the project site during our 1994 site investigation. W:\9911063J\UD001-B.R.DOC\30-Jul-99\SDG 3-1 SECT10KTHREE Site Conditions «M* 3.3 SURFACE CONDITIONS *" The entire 8.2-acre project site is located within a previously graded roughly triangular lot. The _ lot is bounded by Priestly Drive to the southwest, the developed Lot 13 to the southeast, El Camino Real to the northeast, and the developed Lots 4 and 5 to the northwest (Figure 2). Fill slopes up to about 8 feet in height and inclined a 2:1 (horizontal to vertical) ascend from a — portion of the northwestern side of the lot and descend from the southeast side of the existing pad. In addition, a cut and fill slope up to about 8 feet in height and inclined at about 5:1 descends to El Camino Real. The graded pad portion of Lot 12 gently slopes from the east to the — west. A concrete driveway entrance is currently located at the northwest corner of the site. ** Vegetation on the graded pad generally consist of a moderate growth of grasses and weeds. The w slopes and landscaped parkways separating the property from the bordering roadways and lots have been planted with grass and trees and are irrigated. There are several piles of ""* undocumented fill and debris along the southwestern side of the graded pad. 3.4 SUBSURFACE CONDITIONS _ The site is underlain by fill soil, the Eocene Santiago Formation, and the Cretateous Point Loma Formation. Fill soil was encountered up to 16 feet during our 1994 investigation. The typical *"" depth of fill appears to be about 10 feet across the pad. The fill is generally composed of highly _ to very highly expansive lean and fat clay. A cut area is indicated along the extreme southern portion of the site. The approximate location of the cut/fill boundary as reported in the 1982 San Diego Soils report is shown on Figure 2. Variations in the actual cut/fill boundary line should be ~* expected. — Our review indicates that the Santiago Formation exists at depth at the extreme southern edge of the site. This formational material is composed of medium dense to dense, poorly graded sand with silt. The Santiago Formation may be exposed at the surface in the extreme southern portion *• of the site. The results of our review indicate that the Point Loma Formation underlies the fill soil over a _ majority of the site. In addition, the Point Loma Formation may be exposed in a cut area in the southwestern portion of the site. This formational material is primarily composed of hard and very hard claystone. These materials are classified as lean and fat clays when excavated and are *• considered highly to very highly expansive. 3.5 GROUNDWATER•** No groundwater, surface seeps, springs, or unusually wet areas were observed during our field *" studies nor indicated in the review geologic and geotechnical investigation reports. Groundwater «•> is not expected within the depths of excavation. Perched or shallow groundwater conditions may develop after construction within the clayey soil. W:\9911063J\UKW1-B.R.DOC\30-Jul-99\SDG 3-2 SECTIONFOUR Discussions. Conclusions and Becommendations The discussions, conclusions, and recommendations presented in this report are based on information provided to us, a review of available information, results of our site reconnaissance, empirical correlations, engineering evaluations and analyses, and professional judgment. The conclusions and recommendations presented in our August 8, 1994 report are still applicable with the following changes and additions. 4.1 GEOLOGIC AND SEISMIC HAZARDS The primary geologic and seismic hazard potentially affecting the site is moderate to severe ground shaking in response to either a local moderate or more distant large magnitude earthquake during the life of the planned facility. No known active faults cross the site, and the area is not within a Alquist-Priolo Special Studies Zone for fault rupture hazard. The existing surface and subsurface conditions indicate that the probability of hazards such as slope instability, subsidence, soil liquefaction, and flooding affecting the site would be considered very low. 4.2 SITE EARTHWORK We anticipate that earthwork for the project will generally consist of minor regrading of the relatively level site, excavation of existing soil within building and pavement areas, compaction of a select fill cap, and the excavation and backfilling of utility trenches. We recommend that fat clays or deleterious materials be removed from the site. We recommend that the building foundations be founded entirely on compacted fill soil to provide uniform support for the foundations and floor slabs. We recommend that a pre-grading conference be held at the site with the owner, contractor, civil engineer, and geotechnical engineer in attendance. 4.2.1 Soil Characteristics The fill and near-surface formational soil present at the site consists primarily of lean to fat clay with some silty sand to poorly graded sand with silt at the extreme southern end of the site. The grading and design recommendations presented in this report are based on the assumption that soil similar to the soil observed at the surface during our site reconnaissance and described in our previous reports currently exist near the proposed finish grade elevations. It is our opinion that the formational soil within the anticipated excavation depths can be excavated with moderate to heavy effort with conventional excavating equipment; fill soil can be excavated with moderate effort. Because of the highly expansive nature of the onsite soil, We recommend that the near surface soil be excavated and properly disposed of offsite, or be used in landscape areas. 4.2.2 Site Preparation A majority of the near surface soil is unsuitable for building foundation loading and pavement subgrades. We recommend that subgrade soil within four feet of finish grade in the building and exterior hardscape areas and within two feet of subgrade in the pavement areas consist of nonexpansive to low expansive select soil. Select soil shall consist of material that contains no ti!l$ GMlR6f¥lQQflW3fll CMC W:\9911063J\UD001-B.R.DOC\30-Jul-99\SDG 4-1 SECTIONFOUR Discussions, Conclusions and Recommendations rocks or hard lumps greater than 6 inches in maximum dimension, have at least 40 percent material less than V* inch in size, have an Expansion Index of 30 or less when tested in accordance with UBC Standard 29-2, and does not have any perishable, spongy, deleterious, or otherwise unsuitable material. Building areas are defined as the building limits plus a horizontal distance of five feet outside of the building limits. Based on the available information, we do not anticipate that the existing soil at the site will be classified as select material. Our firm should test all planned borrow soil prior to import to the jobsite to verify compliance with the requirements for select material. Lime treatment of soil beneath pavement areas could improve the subgrade support without removing two feet of subgrade. Lime treatment is discussed further in Section 4.9 of this report. Loose and organic topsoil from the landscaped areas should also be removed and disposed of offsite or in landscape areas. In addition, we recommend that prior to the start of earthwork operations, stockpiles of soil, and other debris be removed and disposed offsite. Abandoned underground utilities should either be excavated and the trenches properly backfilled, or the lines completely filled with sand-cement slurry. We recommend that the tree roots be excavated from trees that are to be removed in the building area. We recommend that select fill soil at the site be placed and compacted at a moisture content at or above the optimum moisture content. Fill soil consisting of excavated fill or formational materials should be place and compacted at a moisture content of at least three percent above the optimum moisture content. We recommend that the proposed grading be performed in accordance with Section 300 of the most recent approved editions of the "Standard Specifications for Public Works Construction" and "Regional Supplement Amendments" for earthwork and other related site activities. In general, all fill and backfill should be compacted to a minimum relative compaction of 90 percent when tested in accordance with ASTM D1557; moisture contents during placement should be in excess of the optimum moisture content. We recommend that URSGWC observe the grading operations and test the compacted fill. We understand that at this time no subterranean structures are planned for this project site. However, minor temporary slopes may be required during grading operations. All temporary excavations should comply with local safety ordinances. The safety of all excavations is the responsibility of the contractor. Generally, temporary excavations through the fill could be sloped at 1:1 up to a maximum depth of 10 feet. For higher cuts, slopes should be inclined at IVi: 1 (horizontal to vertical). It is not anticipated that groundwater dewatering would be required for the excavations. 4.3 SURFACE DRAINAGE We recommend that positive measures be taken to properly finish grade the site so that drainage waters are directed off the site and away from foundations and floor slabs. Even when these measures have been taken, experience has shown that a shallow groundwater or surface water conditions can and may develop in areas where no such water condition existed prior to site development; this is particularly true where a substantial increase in surface water infiltration W:\9911063J\UD001-B.R.DOC\30-Jul-99\SDG 4-2 SECTIONFOUR Discussions, Conclusions and Recommendations results from landscaping irrigation. It is particularly critical at this project site to control surface drainage in order to reduce heaving of the highly expansive subsurface soil. To further reduce soil expansion and moisture related problems, we recommend that landscaping and irrigation be kept as far away from the building perimeter as possible. Irrigation water, especially close to the building, should be kept to the minimum required level. We recommend that the ground surface in all areas be graded to slope away from the building foundations and floor slabs and that all runoff water be directed to proper drainage areas and not be allowed to pond. A minimum ground slope of two percent is suggested for unpaved areas and one percent for paved areas. 4.4 SUBSURFACE DRAINAGE The proposed grading scheme will result in placement of a cop of select material over the entire site area. The select soil is typically much more permeable than the underlying clayey fill or formational soil. Thus, the select cap can act as a collection zone for infiltrated water and aid in buildup and horizontal migration of water. In our opinion, the most efficient method of controlling subsurface water in the more permeable select fill cap and preventing ponding on the less permeable and highly expansive clay fill is to install a perimeter subdrain system around the entire building and to install a subdrain system in the landscaped areas. The subdrain should collect the subsurface water in the select fill and direct the water offsite. The perimeter subdrain should be a minimum of 18 inches wide and consist of 1-inch maximum crushed rock wrapped in filter fabric and a 4-inch diameter perforated PVC or ABS drain pipe conforming to the ASTM Designations 1785 and 1751, respectively. The perimeter drain should be a minimum of 4l/2 feet deep (or a minimum of 6-inches below bottom of the select fill) and be located a minimum of 2 feet away from building foundations. The perforated pipe should slope a minimum of 0.2 percent towards the outlet. A 4-inch diameter solid pipe should slope from the subdrain to the drainage outlet location. Landscaping drains should be a minimum of 2l/2 feet deep (or a minimum of 6-inches below the select fill) within the landscape areas. The perforated pipe should slope a minimum of 0.2 percent. A 2- to 4-inch diameter solid pipe should slope from the subdrains to the drainage outlet location. At locations where the subdrain intersects existing utility trenches, we recommend that an impermeable liner be used to prevent water in the subdrain from infiltrating the more permeable trench backfill beneath the building. 4.5 FOUNDATIONS We have recommended that the proposed building pad areas be directly underlain by properly compacted select fill. It is our opinion that the building structures may be supported on conventional spread or continuous footings. We recommend that these shallow footings be designed for an allowable soil bearing pressure of 3,000 pounds per square foot (psf) and be at least 24 inches deep and 24 inches wide. All continuous footings should be reinforced top and bottom with steel bars. Footings should be designed for approximately one inch of heave over a distance of 50 feet. The project structural engineer should design the footings to accommodate W:\9911063J\UD001-B.R.DOC\30-Jul-99\SDG 4-3 SICTIOHFOUR Discussions, Conclusions and Recommendations these deflections. The bearing capacity may be increased by one-third for loads that include wind or seismic forces. We recommend that foundation excavations be cleaned of loose material and that the excavations be observed by a qualified engineer or geologist prior to placing steel or concrete to verify soil conditions exposed at the bottoms of the excavations. Resistance to lateral loads on the shallow foundations will be provided by passive resistance along the edge of the footings and frictional resistance along the bottom of the footings. For passive resistance, we recommend that an equivalent fluid weight of 300 pounds per cubic foot (pcf) be used for footings or grade beams poured neat against the excavation or properly backfilled. This value assumes a horizontal surface for the soil mass extending at least 10 feet from the face of the footing, or three times the height of the surface generating passive resistance, whichever is greater. The upper 12 inches of material in areas not protected by floor slabs or pavement should not be included in design for passive resistance. If friction is to be used to resist lateral loads, we recommend using a coefficient of friction of 0.4 between the soil and foundation concrete. If it is desired to combine frictional and passive resistance in design, we recommend using a friction coefficient of 0.3. We estimate that the total foundation settlements may vary from !/2 to 1 inch with differential settlements about half of that amount. We anticipate that a majority of the foundation settlement will occur during construction. Following construction and site development, foundation heaving is likely to be the predominate mode of ground movement. The magnitude of ground movement can be reduced by using select fill materials, reducing water infiltration into the highly expansive soil, and by other recommendations presented in this report. 4.6 SEISMIC COEFFICIENT We understand that the 1997 Unified Building Code (UBC) will be used for design of the proposed buildings and parking structure. We recommend that the values listed below be used for design: Soil Profile Seismic Zone Zone Factor, Z Seismic Source Type So 4 0.4 B 1 997 UBC Reference Table 16-J Figure 16-2 Table 16-1 Table 16-U The project site is approximately 11 kilometers from the Rose Canyon Fault (to be used in Table 16-T). 4.7 SUBTERRANEAN WALLS Subterranean walls, if any, should be designed to resist the pressure exerted by retained soil plus any additional lateral forces due to loads placed adjacent to or near the wall. For drained W:\9911063J\UD001-B.R.DOC\30-Jul-99\SDG 4-4 SECTIONFOUR Discussions, Conclusions and Recommendations*• conditions, we recommend that site retaining walls be designed for an equivalent fluid weight of M 45 pcf. If surcharge or floor loads are planned adjacent to the walls, the walls should be designed to resist a uniform horizontal pressure equal to 30 percent of the floor or surcharge load. These pressures are based on horizontal backfill surface conditions, the use of on-site select soil ** for backfilling the walls, and adequate drainage to prevent buildup of hydrostatic pressure in the .„* backfill. If other loading conditions are to be considered in the vicinity of the walls, we should be advised so that additional recommendations can be provided. 4.8 SLABS-ON-GRADE *" We recommend that the slab-on-grade concrete floors for light office loading be designed for a — minimum thickness of four inches. Concrete slabs should be provided with control joints at regular intervals of approximately 15 feet, each way. We recommend that the slab-on-grade concrete floors be designed for a minimum thickness of five inches. Concrete slabs should be "*•* reinforced with at least No. 4 steel reinforcing bars placed at 18 inches on-center each way. The ^ steel reinforcement should not extend through the control joints. Concrete and control joints should be placed in accordance with the practices recommended by the American Concrete ~* Institute. "" We recommend that concrete slabs-on-grade be underlain by a minimum four inches underlay of ^ clean, coarse sand. A vapor barrier (e.g., 10-mil visqueen) with a two inch protective sand cover should be placed beneath areas that will have moisture-sensitive floor coverings (such as J^u carpeting or linoleum). The two inch cover can be part of the four inch underlay. To further reduce the likelihood of moisture intrusion through the concrete slab-on-grade floors, — we suggest that the vapor barrier be extended below interior and exterior footing excavations. Our experience indicates that many post-construction slab moisture issues originate near the ~" interior and exterior footings. Moisture flow in these areas is most pronounced because there is ™ generally no vapor barrier, and the concrete footings tend to upwick moisture from the soil. The coefficient of friction between the footing concrete and soil should be reduced to 0.2 if the vapor'•<**barrier extends beneath the foundations. xm 4.9 PAVEMENTS *" We recommend that the top six inches of subgrade be compacted to at least 95 percent of the maximum dry density as determined by ASTM Test Method D1557. We recommend that subgrade suitability tests be performed for the near surface soils at the time of grading to evaluate the required pavement thicknesses. "" We recommend that aggregate base should conform to the current Standard Specifications for « Public Works Construction (Green Book) 200-2.2.2. The aggregate base materials should be placed at a minimum relative compaction of 95 percent. Asphalt concrete should conform to the "* Green Book, Section 203-6.2.1 for the asphalt and Section 203.6.2.2 for the aggregate. PCC *"• should conform to Section 201 of the Green Book. The paving operations should be inspected by a qualified testing laboratory. We recommend that a qualified engineer observe and test the compaction of subgrade and base materials. urn W:\9911063J\UD001-B.R.DOC\30-Jul-99\SDG 4~5 SECTIONFOUR Discussions, Conclusions and Recommendations Lime treatment of the subgrade beneath pavement areas should be considered as an alternative to removing the two feet of subgrade and replacing it with select fill. Lime stabilization of subgrade involves adding lime and water to expansive soil, which decreases the swell potential and improves the load-deformation performance. Lime treatment is a common procedure and routinely performed for roadway and parking applications. Some additional field and laboratory work would be necessary to evaluate whether the onsite soil is chemically suitable for lime stabilization. We recommend that adequate surface drainage be provided to reduce ponding and possible infiltration of water into the base and subgrade materials. We suggest that paved areas have a minimum gradient of one percent. It is important to provide adequate drainage to reduce possible future ponding and possible distress of the pavement section. As much as possible, planter areas next to pavements should be avoided; otherwise, subdrains should be used to drain the planter to appropriate outlets, and the planters should be lined to reduce moisture infiltration beneath pavements. We also recommend that concrete curbs bordering landscape areas have a deepened edge to provide a cutoff for moisture flow beneath the pavement. Generally, the edge of the curb can be extended an additional 12 inches below the base of the curb. The deepened edge should have a thickness of approximately six inches. If requested, URSGWC can perform subgrade suitability tests for the on site soils, and provide pavement thickness recommendations. 4.10 CORROSION POTENTIAL We recommend that corrosion potential tests be performed on the near-surface soil, and that proper engineering solutions be performed to mitigate the effects of corrosive soil present onsite, if any. If desired, a corrosion engineer should be consulted for additional design information. W:\9911063J\UD001-B.R.DOC\30-Jul-99\SDG 4~6 SECTIONFIVE Uncertainty and Limitations The recommendations made herein are based on the assumption that soil conditions do not deviate appreciably from those found during our site reconnaissance and reported in previous studies. We recommend that URSGWC review the foundation and grading plans to verify that the intent of the recommendations presented herein has been properly interpreted and incorporated into the contract documents. We further recommend that the site grading and earthwork, subgrade preparation under concrete slabs and paved areas, utility trench backfill, and foundation excavations be observed by a qualified engineer or geologist to verify that site conditions are as anticipated, or to provide revised recommendations, if necessary. This report is intended for design purposes only and may not be sufficient to prepare an accurate bid. Geotechnical engineering and the geologic sciences are characterized by uncertainty. Professional judgments presented herein are based partly on our understanding of the proposed construction, and partly on our general experience. Our engineering work and judgments rendered meet current professional standards; we do not guarantee the performance of the project in any respect. MRS GfOlOQf Hf00ltW8Fi GljfllO W:\9911063J\UD001-B.R.DOC\30-Jul-99\SDG 5-1 f i I I i I i I a I i I I i i I i i i i t I i f "REPRODUCED WITH PERMISSION GRANTED BY THOMAS BROS. MAPS. THIS MAP IS COPYRIGHTED BY THOMAS BROS. MAPS. IT IS UNLAWFUL TO COPY TO REPRODUCE ALL OR ANY PART THEREOF. WHETHER FOR PERSONAL USE OR RESALE, WITHOUT PERMISSION." VICINITY MAP CARLSBAD RESEARCH CENTER - LOT 12 FN: LOT12 PM: RJ CHECKED BY:DATE: 7-27-99 PROJECT NO: 58-9911063J.OO-UD001 FIG. NO: 1 URS Qnlner Woodward Clyde LOT 4 LOT 5 SOURCE: SMITH CONSULTING ARCHITECTS LEGEND INDICATES APPROXIMATE LOCATION OF CUT/RLL "DAYLIGHT" LINE (SAN DIEGO SOILS ENGINEERING, 1982) INDICATES APPROXIMATE LOCATION OF PROPOSED OFFICE BUILDING 200 APPROXIMATE GRAPHIC SCALE (FED SITE PLAN CARLSBAD RESEARCH CENTER - LOT 12 FN: LQT12 PM: RJ CHECKED PROJECT NO: 58-9911063J.OO-UD001 DATE: 7-27-99 FIGURE NO: 2 URS Grelner Woodward Clyde