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Home My WebLink About3593; Geotech Reconnaissance Faraday Avenue Extension; Geotechnical Reconnaissance; 1998-05-28Leighton and Associates GEOTECHNICAL CONSULTANTS GEOTECHNICAL RECONNAISSANCE, FARADAY AVENUE EXTENSION, CARLSBAD, CALIFORNIA Project No. 4980118-001 May 28, 1998 Prepared For: O'DAY CONSULTANTS 2320 Camino Vida Roble, Suite B Carlsbad, California 92009 3934 MURPHY CANYON ROAD, SUITE B205 SAN DIEGO, CA 92123-4425 (619) 292-8030 • FAX (619) 292-0771 Leighton and Associates GEOTECHNICAL CONSULTANTS May 28,1998 To:O'Day Consultants 2320 Camino Vida Roble, Suite B Carlsbad, California 92009 Project No. 4980118-001 Attention: Mr. Chuck Collins Subject:Geotechnical Reconnaissance Faraday Avenue Extension, Carlsbad, California Enclosed is the Geotechnical Reconnaissance for the Faraday Avenue Extension for inclusion into the Environmental Impact Report as requested. Please note that the Geologic Maps have been labeled Figures 1 through 4. We are currently in the process of preparing our geotechnical investigation of the site and will issue this document shortly. If you have any further questions or requests, please do not hesitate to contact this office. We appreciate this opportunity to be of service on this project. Respectfully submitted, LEIGHTON AND ASSOCIATES, cc: . Franzone, RCE 3 r of Engineering Mr. Tim Gnibus Cotton Beland, Associates 6310 Greenwich Drive, Suite 220 San Diego, California 92122 MichafclR/Stewart~CEG t349 Director of Geology p. 12/31/99) 3934 MURPHY CANYON ROAD, SUITE B205 SAN DIEGO, CA 92123-4425 (619) 292-6030 • FAX (619) 292-0771 GEOTECHICAL/SOILS ENVIRONMENTAL SETTING Geologic Conditions The majority of the project site is presently developed as agricultural fields and has been partially graded and disturbed in order to facilitate the agricultural activities onsite. Topographically, the site is characterized by numerous ridges and intervening ravines and valleys that intersect a main northwest trending drainage that flows into Agua Hedionda Lagoon. Elevations along the proposed alignment range from approximately 20 feet mean sea level (m.s.l.) at the extreme northwest corner of the site in the main drainage, to approximately 265 feet mean sea level (m.s.l.) near the ridgeline along the eastern edge of the alignment. Natural slopes on the site range from relatively steep (steeper than 1:1, horizontal to vertical) to relatively gentle (less than 3:1, horizontal to vertical). Existing improvements are generally related to past and present agricultural activities on the site. Improvements associated with the agricultural fields include underground irrigation lines and valves and minor cuts and fills associated with access roads. Other onsite improvements include: access roads associated with several utility easements, and a pair of relatively small earthen dams constructed to impound water for irrigation purposes. Non-agricultural vegetation on-site ranges from a relatively thick growth of grasses and weeds on the undisturbed hillsides to shrubs and thick weeds in the ravines. Riparian trees and shrubs grow quite heavily in the main drainage trending northwest-southeast across the site. The majority of the proposed alignment transects hillside agricultural fields. Regional Geology The subject site is located within the coastal subprovence of the Peninsular Ranges Geomorphic Provence, near the western edge of the southern California batholith. The topography at the edge of the batholith changes from rugged landforms developed on the batholith to the more subdued I and forms which typify the softer sedimentary formations of the coastal plain. Site Geology As encountered during our investigations), and our review of geotechnical reports applicable to the subject site (Appendix A), the majority of the proposed alignment is underlain by the Tertiary Santiago Formation. The Jurassic-aged Santiago Peak Volcanics is the bedrock unit in the extreme southeast section of the alignment. Surficial units on-site consist of alluvium, colluvium, topsoil, and undocumented fill soils. The approximate areal distributions of the units are shown on the Geologic Maps (Figures 1 through 4) and briefly discussed below. Jurassic Santiago Peak Volcanics (Map Symbol - Jsp) The Jurassic aged Santiago Peak Volcanics crop out in the southeast portion of the subject site. Typically the unit is hard and extremely resistant to erosion and forms topographic highs. Most of the rocks are dark greenish gray where fresh but weather grayish red to dark reddish brown. The soil developed on the Santiago Peak Volcanics is the color of the weathered bedrock and supports the growth of dense chaparral. If deep removals are planned in this area, localized heavy ripping or blasting may be required. Santiago Formation (Map Symbol — Ts) The bedrock unit underlying the majority of the site is the Tertiary-aged Santiago Formation. In general, the unit consists of massive to weakly bedded sandstone with interbedded clayey siltstone and silty claystone. The sandstone encountered consisted primarily of light gray, light brown, and light yellow-brown, moist, dense, silty, fine- to occasionally medium-grained sandstone. The sandstone was generally friable, slightly micaceous and weakly bedded to massive. Well cemented sandstone beds were occasionally encountered during this and previous investigations on adjacent sites and may require heavy ripping during grading. The siltstone typically consisted of brown and olive-green gray, moist, stiff, clayey siltstones that were fissile to indistinctly bedded and contained calcium carbonate, manganese-oxide and iron-oxide staining. The claystone typically was gray to brown, moist, stiff to hard, fine-grained, sandy to silty claystone that was moderately sheared. Where encountered, the upper 6 to 12 inches of the Santiago Formation appears to be moderately weathered, porous and potentially compressible. This layer should be removed and recompacted in areas of structural fill placement or settlement sensitive improvements. Alluvium (Map Symbol - Qal) Alluvium was encountered during our investigation of the proposed alignment in the majority of the drainages and the low lying areas adjacent to and along the proposed alignment. As encountered, the alluvium generally consisted of potentially compressible, moist to wet, loose to medium dense silty sands, sandy silts, and sandy clays. Within the main northwest trending drainage, the alluvium is relatively thick as evidenced by approximately 20-50 feet of alluvium encountered in borings excavated for the adjacent golf course geotechnical investigation. In many of the smaller side canyons, alluvium was encountered and mapped. However, these areas were not accessible with the drilling equipment utilized in this investigation. Based upon our work on adjacent properties and our experience with similar conditions, alluvial depths in these areas can be expected to range up to 10 +feet. Unsaturated alluvial soils are considered potentially compressible and not suitable for the support of structural loads or additional fill soils in areas of settlement sensitive improvements. These soils should be removed and recompacted in areas proposed for structural improvements as part of site grading. Colluvium/ Slope Wash (Map Symbol - Qcol) Holocene aged colluvium / slope wash was encountered mantling the lower valley slopes, in areas undisturbed by agricultural activities. As encountered, the colluvium / slope wash typically consisted of poorly consolidated surficial materials derived from nearby soil and decomposed bedrock sources. This reworked debris is deposited along the flanks of the lower valley slopes by the action of gravity and surface water. Generally, the material was light brown to dark brown, damp to moist, medium dense, silty to clayey sand that was generally 5 to 15 feet in thickness although locally it may be deeper. The colluvium / slope wash was typically porous and anticipated to be potentially compressible under the load of existing fills or improvements. In places, it is difficult to distinguish the sandier colluvial soils from the underlying weathered Santiago Formation. Topsoil (Unmapped) Topsoil was encountered essentially covering the entire site but was not mapped. The topsoil was found to be generally light brown to dark brown, damp, loose to medium dense, silty sands with minor amounts of clay. The topsoil was generally ± 3 feet in thickness and contains moderate amounts of decomposed organics. Where disturbed by the previous agricultural activities, the topsoil may locally be up to 5 feet thick. This unit was evaluated to be compressible under the loading of fill soils or other improvements. UndocumentedFill (Map Symbol - Af) Undocumented fill soil is present on the site in various locations. The major undocumented fill areas consisted of earthen embankments for agricultural ponds, unimproved roads, end-dumped debris piles, and utility trench backfill. Our site reconnaissance indicated that potentially compressible alluvium was left in place beneath these fill areas. In addition, our literature review did not indicate that any documentation or testing was completed for these areas. Undocumented fill soils were also noted in several other locations within the subject site. As encountered, the undocumented fill consisted of numerous soil types, but typically the fill soils were light brown to medium brown and gray, moist to very moist, loose, silty sands and clayey sands. These soils should be removed to expose competent material in areas of proposed fill soils or improvements. Geologic Structure The bedrock units encountered on the site were generally massive to weakly bedded. However, based on our professional experience in the area, bedding of the underlying Santiago Formation is anticipated to be relatively gently dipping (i.e. 5 to 10 degrees) to the west. Ground Water Ground water was encountered within several of the onsite drainages in the lower elevations of the site particularly in the main northwest trending drainage located west of the proposed alignment. The presence of ground water in these areas would most likely limit the removal of alluvium and undocumented fill that would be required for structural improvements proposed for these areas. Perched groundwater conditions were also encountered in several of our borings on-site commonly at the contact between the relatively impermeable Tertiary Santiago Formation and the relatively porous overlying soils. However, ground water is not anticipated to be a constraint to site development provided the recommendations provided in the project geotechnical investigation and during the course of grading are implemented. Mass Movement Based on our review of the previous geotechnical reports, available geologic literature and maps, and aerial photographs, several features indicative of mass movements (such as landslides, surficial slumps, etc.) were observed within the areas proposed for development. In the central and north-central portion of the proposed alignment an area has been mapped as a landslide complex based on topographic expression and data gathered during our subsurface investigation. Geologic mapping of excavations in this area should be performed during site grading. Localized zones of weak claystone/siltstone material are present in the Santiago Formation and may create localized areas that are prone to slope instability if exposed in a cut slope. Accordingly, all cut slopes should be mapped by an engineering geologist during site grading. Additional recommendations for slope stabilization can be provided as needed during site grading. Faulting and Seismicitv Our discussion of the faults on the site is prefaced with a discussion of California legislation and state policies concerning the classification and land-use criteria associated with faults. By definition of the California Mining and Geology Board, an active fault is a fault which has had surface displacement within Holocene time (about the last 11,000 years). The State Geologist has defined a potentially active fault as any fault considered to have been active during Quaternary 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 most recently revised in 1994. The intent of this act is to assure that unwise urban development does not occur across the traces of active faults. Base on our review of the Fault-Rupture Hazard Zones, the subject site is not located within any Fault-Rupture Hazard Zone as created by the Alquist-Priolo Act (Hart, 1994). However, several inactive fault zones have been mapped in a number of places within and adjacent to the subject site (see attached Geologic Maps, Figures 1 through 4). These inactive fault zones are not considered to be a constraint to site development. The location of the proposed development can be considered to lie within a seismically active region, as can all of southern California. The subject site lies within Seismic Zone 4 as outlined in Section 1629 of the 1997 edition of the UBC. The Rose Canyon Fault Zone which is located approximately 4.5 miles to the west of the site is considered to have the most significant seismic effect at the site from a design standpoint. A maximum probable earthquake of moment magnitude 5.9 on the fault could produce a peak horizontal ground acceleration of approximately 0.30g at the site. The slip rate of the fault is estimated at 1.5 mm/yr. (State of California, 1996) and the soil profile type is Sc (per Table 16-J of the 1997 UBC). Seismic Considerations The principal seismic considerations for most structures in southern California are surface rupturing of fault traces, damage caused by ground shaking and/or seismically induced liquefaction or dynamic settlement. The probability of damage due to ground rupture is considered minimal since active faults are not known to cross the site. Ground lurching due to shaking from distant seismic events is not considered a significant hazard, although it is a possibility throughout the southern California region. Ground Shaking The seismic hazard most likely to impact the site is ground shaking resulting from an earthquake on one of the major regional faults. As discussed above, a maximum probable event on the Rose Canyon Fault Zone (considered the design earthquake for this site) could produce a peak horizontal acceleration at the site of 0.30g. Liquefaction/Dynamic Settlement Liquefaction of cohesionless 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. The Santiago Formation is generally not considered liquefiable due to its high density characteristics. From our preliminary field study, it appears that the area most likely susceptible to liquefaction is the main drainage area. Accordingly, as the proposed alignment does not infringe upon the main drainage, it is our professional opinion that the proposed roadway alignment has a low potential for liquefaction. Due to the uneven terrain of the project site, grading will be required in order to achieve the design grades. In certain areas of the proposed alignment, this will require that significant cuts and/or fills be made in order to achieve the design grade. It is our professional opinion that development of the proposed alignment will not be precluded by the soil and geologic conditions at the site. However, remedial measures will be required to ensure stable grading. The presence of loose, potentially compressible surface deposits in the form of topsoil, alluvium, colluvium, and undocumented fill soils will require special consideration during grading. In addition, ground water was observed as runoff in the major drainages and was encountered as seepage in several of our borings. Remedial measures will likely be required to address the groundwater conditions. Loose unconsolidated deposits on the project site should be removed and densified, and subdrains installed where required to reduce the build-up of a shallow groundwater condition. The Safety Element of Carlsbad General Plan establishes requirements for the preparation of geotechnical studies for various land uses. Implementation of the Safety Element of the Carlsbad General Plan requires the compilation of site-specific geotechnical reports for development projects, use of appropriate construction techniques during development as recommended by a registered engineer, and implementation of standards for grading and construction to mitigate geologic hazards during and after development. These strategies will be implemented as development moves forward on the project site. In addition, the final grading plan must comply with the City of Carlsbad Grading Ordinances. Due to site conditions, supplemental measures will be required to reduce the geologic impact from grading to less than significant. Earthquake Hazards While no active faults are known to traverse the subject site, earthquakes along regional faults could produce groundshaking at the site. All development must conform to the most recent version of the Uniform Building Code (UBC), which requires building techniques to prevent structural failure during earthquakes. With the implementation of the UBC requirements, the risk of property damage and injury due to earthquakes will be no greater than the risk encountered in other populated areas of southern California. Cumulative Impacts Geologic conditions vary across the subject site, but all development in the region is potentially subject to groundshaking from an earthquake on one of the active regional faults. As all new development must be constructed according to State-mandated requirements for seismic safety, cumulative geotechnical and soil impacts will not be significant. LEVEL OF SIGNIFICANCE Impacts related to site geotechnical and soil conditions will be potentially significant. While the on-site geologic conditions will not preclude the planned development, remediation measures will be necessary to ensure geologic stability and public safety. MITIGATION MEASURES The following mitigation measures are required to reduce the geotechnical and soil impacts to less than significant. 1. Information and recommendations provided in the Leighton and Associates, Inc., project geotechnical /soils report shall be incorporated into plans for site grading and construction. 2. All grading and subsequent development plans shall be reviewed by a certified engineer and/or engineering geologist prior to finalization to determine the need for additional measures and/or analysis. During the review, special consideration shall be given to the loose, potentially compressible surface deposits in the form of topsoil, alluvium, slopewash, undocumented fill soils, and landslide debris. Such materials will require remedial grading where encountered. LEVEL OF IMPACT AFTER MITIGATION Impacts related to geotechnical and soil conditions will be reduced to less than significant with the implementation of the required mitigation measures. APPENDIX A REFERENCES Abbott, P.L., ed., 1985, On the Manner of Deposition of the Eocene Strata in Northern San Diego County; San Diego Association of Geologists Fieldtrip Guidebook, April 13,1985. Albee, A.L., and Smith J.L., 1966, Earthquake Characteristics and Fault Activity Southern California in Southern California, Association of Engineering Geologists, Special Publication, dated October 1966. Bolt, B.A., 1973, Duration of Strong Ground Motion, Proc. Fifth World Conference on Earthquake Engineering, Rom, Paper No. 292, pp. 1304-1313. dated June 1973. Bonilla, M. J., 1970, Surface Faulting and Related Effects, in Wiegel, R., Ed., Earthquake Engineering, New Jersey, Prentice-Hall, Inc., pp. 47-74. California Division of Mines and Geology, 1975, Fault Map of California, Scale 1"=750,000'. Eisenberg, L.I., 1983, Pleistocene Terraces and Eocene Geology, Encinitas and Rancho Santa Fe Quadrangles, San Diego County, California, San Diego State University Master's Thesis (unpublished),p. 386. , 1985, Pleistocene Faults and Marine Terraces, Northern San Diego County in Abbott, P.L., Editor, On the Manner of Deposition of the Eocene Strata in Northern San Diego County, San Diego Association of Geologists, Field Trip Guidebook, pp. 86-91. Geotechnics, 1992, Phase 1 Geotechnical Investigation, Carlsbad Ranch, Carlsbad, California, Project No. 0054-0001-00,dated September 25,1992. Greensfelder, R.W., 1974, Maximum Credible Rock Accelerations from Earthquakes in California, California Division of Mines and Geology, Map Sheet 23. Hannan, D.L., 1975, Faulting in the Oceanside, Carlsbad, and Vista Areas, Northern San Diego County, California in Ross, A. and Dowlen, R.J., eds., Studies on the Geology of Camp Pendleton and Western San Diego County, California, San Diego Association of Geologists Field Trip Guidebook, pp. 56-60. Hart, 1988, Fault-Rupture Hazard Zones in California, Alquist-Priolo Special Studies Zones Act of 1972 with Index to Special Study Zones Maps: Department of Conservation, Division of Mines and Geology, Special Publication 42. Hart, E.W., 1992, Fault-Rupture Hazard Zones in California, Alquist-Priolo Special studies Zones Act of 1972 with Index to Special Study Zones Maps: Department of Conversation, Division of Mines and Geology, Special Publication 42. APPENDIX A (Continued) Hileman, J.A., Allen, C.R., and Nordquist, J.M., 1973, Seismicity of the Southern California Region, 1 January 1932 to 31 December 1972: California Institute of Technology Seismology Laboratory, Pasadena, California. International Conference of Building Officials (ICBO), 1997, Uniform Building Code. , 1997, Uniform Building Code, Volume I-Administrative, Fire- and Life-Safety, and Field Inspection Provisions; Volume II-Structural Engineering Design Provisions; and Volume Ill- Material, Testing and Installation Provisions: ICBO. Jennings, C. W., 1975, Fault Map of California: California Division of Mines and Geology, Geologic Map No. 1, Scale 1:750,000. , 1992, Preliminary Fault Activity Map of California: California Division of Mines and Geology, Open File Report 92-03, Scale 1:750,000. Joyner, W.B., and Boore, D.M., 1982, Prediction of Earthquake Response Spectra, in Proceeding 51st Annual Convention, Structural Engineers Association of California; Also U.S. Geological Survey Open-File Report 81-977, p. 16. Lamar, D.L., Merifield, P.M., and Proctor, R.J., 1973, Earthquake Recurrence Intervals on Major Faults in Southern California, in Moran, D.E., Slosson, J.E., Stone, R.O., and Yelverton, C.A., Eds., 1973, Geology, Seismicity, and Environmental Impact, Association of Engineering Geologists, Special Publication. Leighton and Associates, Inc., 1985, Preliminary Geotechnical Investigation, Proposed Huntingdon Palomar Business Park, Carlsbad, California, ProjectNo. 4841363-02, dated April 5,1985. , 1987, Preliminary Geotechnical Investigation, Portion of Lot H of Rancho Agua Hedionda, Partition Map No. 823, Northeast Corner of Interstate 5 and Cannon Road, Carlsbad, California, ProjectNo. 8870059-01,dated February 17,1987. , 1989a, Preliminary Geotechnical Investigation, Proposed Carltas Rancho Agua Hedionda Regional Shopping Center, Northeast of Interstate 5 and Cannon Road, Carlsbad, California, ProjectNo. 8891551-01,dated September29,1989. , 1991, Supplemental Geotechnical Evaluation, Proposed College Business Park, Carlsbad Tract 85-17, Carlsbad, California, Project No. 8841363-04, dated January 16, 1991 revised September 24,1991. , 1992, City of Carlsbad Geotechnical Hazards Analysis and Mapping Study, 84 Sheets, dated November, 1992. APPENDIX A (Continued) , 1994b, Preliminary Geotechnical Evaluation for Tentative Map Purposes, Carlsbad Ranch, Carlsbad, California, Project No. 4930489-04, dated July 5,1994. , In-house unpublished data. Lindvall, S.C., Rockwell, T.K., and Lindvall, C.E., 1990, The Seismic Hazard of San Diego Revised: New Evidence for Magnitude 6+ Holocene Earthquake on the Rose Canyon Fault Zone: Proceedings of Fourth U.S. National Conference on Earthquake Engineering, Volume 1, pp.679-688. Moore and Taber, 1987, Report of Geotechnical Services, Carlsbad Tract No. 81-46, Airport Business Center Unit No. I, City of Carlsbad, California, Job No. 285-256, dated February 25,1987. Ploessel, M.R., and Slosson, J.E., 1974, Repeatable High Ground Accelerations From Earthquakes - Important Design Criteria, California Geology, V. 27. Reichle, M.S., and Kahle, J.E., 1990, Planning Scenario for a Major Earthquake, San Diego-Tijuana Metropolitan Area: CaliforniaDivision of Mines and Geology, Special Publication 100. Rick Engineering, 1987, Site Development Plan, College Business Park, Carlsbad Tract No. 85-17, Scale 1 "=100', Job No. 8495C, dated May 1,1985, Revised September4,1987. , 1985, Site Development Plan, College Business Park, Carlsbad Tract No. 85-17, Scale 1"=100', Job No. 8495C, dated May 1,1985, Revised September 4,1987. Schnabel, R., and Seed, H.B., 1973, Accelerations in Rock from Earthquakes in the Western United States, Bulletin of the Seismological Society of America, V. 63, No. 2, pp. 501-516. Seed, H.B., and Idriss, I.M., 1982, Ground Motions and Soil Liquefaction During Earthquakes, Monogram Series, Earthquake Engineering Research Institute, Berkeley, California. Seed, H.B., and Idriss, I.M., and Kiefer, R.W., 1968, Characteristics of Rock Motions During Earthquakes, Journal of Soil Mechanics and Foundations Division, ASCE, V. 95, No. SM5, Proc. Paper 6783, pp. 1199-1218. Singh, A., 1970, Shear Strength and Stability of Man-Made Slopes, in Journal of the Soil Mechanics and Foundations Divisions, ASCE, No. SM6,pp. 1879-1892. , 1982, Recent Slope failures, Ancient Landslides and Related Geology of the North-Central Coastal Area, San Diego County, California, California Division of Mines and Geology, Open File Report 82-12, LA. -, 1963, Geology and Mineral Resources of San Diego County, California: California Division of Mines and Geology, County Report 3,309p. APPENDIX A (Continued) U.S. Departmentof the Navy, 1969, Civil Engineering,DM-5. , 1982, Foundations and Earth Structures, DM 7.2. , 1986, Soil Mechanics, DM 7.1. United States Department of the Interior Geologic Survey, 1968, 7.5-Minute Encinitas Quadrangles, Scale 1:24,000, Photo Revised 1975. United States Department of the Interior Geologic Survey, 1996, Probabilistic Seismic Hazard Assessment for the State of California, Open File Report 96-706. Wilson, K.L., 1972, Eocene and Related Geology of a Portion of the San Luis Rey and Encinitas Quadrangles, San Diego, California. Ziony, J.I., and Yerkes, R.F., 1985, Evaluating Earthquake and Surface-Faulting Potential 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. Leighton and Associates GEOTECHNICAL CONSULTANTS January 19,1999 ProjectNo. 980118001 To: O'Day Consultants 5900 Pasteur Court, Suite 100 Carlsbad, CA 91008 Attention: Mr. John StromingerFAX 760 931-8680 Subject: Geogrid Reinforcement for 1-1/2:1 Slopes, Faraday Avenue, Carlsbad, CA Reference: Leighton and Associates, 1998, Geotechnical Investigation for Proposed Faraday Avenue Extension, Alternate 8 Split, Carlsbad, CA, dated July 1,1998, Project No. 4980188-001 In accordance with your request, we have performed preliminary calculations for the geogrid reinforcement of the 1-1/2:1 slopes on the Faraday Avenue Extension in Carlsbad, CA. The following two sheets provide a detail of the recommended slope reinforcement for Stations 47+00 to 50+70 and for Stations 50+70 to 54+70. Geogrid reinforcement ranges from 2 to 3 feet on center (Stations 47+00 to 50+70) to 3 to 4 feet on center (Stations 50+70 to 54+70). The geogrid may be Tensar UX1400, Mirafi 5T, or Strata-Grid 200+. Final design will be based on test results of actual materials proposed to be used in the buttress. If you have any questions, please do not hesitate to contact this office. We appreciate the opportunity to be of service. Respectfully submitted, LEIGHTON AND ASSOCIATES, INC. .Franzone)RCE39552 tor of Engineering Distribution: (2) Addressee Attachments: (2) Slope Reinforcement Details 3934 MURPHY CANYON ROAD, SUITE B205 SAN DIEGO, CA 92123-4425 (619) 292-8030 • FAX (619) 292-0771 FARADAY AVENUE (STATION 47+00 to 50+70) \"=lo' S133HS OOC frfrfCi: S133HS 001 Ctl*CCc i aauc nc i tf i -r^ FARADAY AVENUE (STATION 50+70 to 54+70) - £L. - o "7 = io SJ.33HS OOC trfrl-2£ S133HSOOI Cfrl-ZC S133HS OS IM-CZ Leighton and Associates GEOTECHNICAL CONSULTANTS MEMO To: O'Day Consultants, Mr. John Strominger FAX 760 931 -8680 From: Leighton and Associates, Joe Franzone Date: August 18,1998 Subject: ConstructionDelay, Faraday Avenue, Carlsbad, CA Reference: Leighton and Associates, 1998, Geotechnical Investigation for Proposed Faraday Avenue Extension, Alternate 8 Split, Carlsbad, CA, dated July 1, 1998, Project No. 4980188-001 In accordance with your request, we have performed preliminary calculations for (planning-level purposes only) regarding the acceleration of the settlement and the reduction in the construction delay for the 2 major Faraday Avenue alluvial areas. Based on the results of our investigation, we provide the following: Alluvia! Area B-2/B-3 B-4/B-5 Anticipated Settlement (Inches) 7 to 9 4 to 6 Maximum Design Fill Load (feet) 30 5 to 10 Our calculations indicate that additional remedial action (such as a surcharge fill of the following height above design grade or the installation of wick drains through the saturated alluvial soils at the following spacing) will decrease the approximate construction delay as follows: RecorameiXlPfplpliictionDelay Alluvial Area B-2/B-3 B-4/B-5 Without Remedial Action 100-120 days 180-200 days Surcharge Fill Height 10ft 100 days 150 days 20ft 90 days 100 days 30ft 80 days 80 days Wick Drain Spacing 3ft 60 days 70 days 4ft 90 days 100 days 5ft 100 days 130 days Additional calculations and analysis should be performed if one or a combination of the above remedial actions are chosen. We have assumed Nilex Mebra 7407 Wick Drains for our analysis. Of course, the above is only a rough estimate of the time of the recommended construction delay. The actual construction delay can only be evaluated based on the results of a settlement monitoring program of the actual embankment materials after the roadway construction has been completed. md/O'DayFaraday 3934 MURPHY CANYON ROAD, SUITE B205 SAN DIEGO, CA 92123-4425 (619) 292-8030 • FAX (619) 292-0771 Leighton and Associates GEOTECHNICAL CONSULTANTS Novembers, 1998 Project No. 9801118-002 To: O'Day Consultants 5900 Pasteur Court, Suite 100 Carlsbad, California 92008-7317 To: Mr. John Strohminger Subject: Update Letter and Additional Design Recommendations, Faraday Avenue Extension, Carlsbad, California Reference: Leighton & Associates, 1998, Geotechnical Investigation for the Proposed Faraday Avenue Extension, Alternate 8 Split, Carlsbad California, Project No 4980118-001, dated July 1, 1998 O'Day Consultants, 1998, Grading and Drainage Plans of Faraday Avenue, Sheets 1-15, Project No 3593, DWG 369-2,70% Submittal dated November 3, 1998 Introduction In accordance with your request we have prepared this update letter for the subject project. In addition, this letter provides some additional recommendations for the site development. In general, site conditions remain essentially as described in our geotechnical report referenced above. Accordingly, the recommendations presented in that report remain pertinent and applicable. This letter does, however, present additional recommendations based on design alterations since review of the preliminary plans. Settlement Monitor ins It has been determined that in order to accelerate the settlement of the saturated alluvial soils that will remain in place after removals, a surcharge of 10 feet of fill will be placed above the design finish grade. The areas where the surcharge is required are located between Station 13+95 and 19+00 (Surcharge Area 1), and between Station 35+40 and 37+10 (Surcharge Area 2). With a 10-foot surcharge, Surcharge Area 1 is anticipated to have a settlement time of approximately 100 days. Surcharge Area 2 is anticipated to have a settlement time of approximately 150 days. During the settlement monitoring period, settlement sensitive improvements such as curbs, gutters, sidewalks, pavement, and settlement sensitive utilities that cross the surcharge area should not be installed. Storm drain lines which extend down the canyon areas (perpendicular to the road center line) and which have significant fall can be installed as these lines will not be crossing areas where significant differential settlement is anticipated. 3934 MURPHY CANYON ROAD, SUITE B205 SAN DIEGO, CA 92123-4425 (619) 292-8030 • FAX (619) 292-0771 980118-002 The above mentioned duration of settlement are approximate due to the possibility of unknown conditions that may exist in the subsurface. The actual duration of the settlement monitoring period will be dependent on actual survey data of settlement monuments. We recommend that at-grade settlement monuments be installed at the following stations after the completion of site grading. Surcharge Area 1 14+00 15+00 16+00 17+00 18+00 19+00 Control Surcharge Area 2 35+00 36+00 36+00 37+00 Control The settlement monuments should be surveyed approximately every two weeks with data forwarded to the geotechnical consultant for review. Surcharge soils should be compacted to a minimum relative compaction of 90 percent to reduce the potential for settlement of the surcharge fill to affect the survey readings. When the data indicates that a majority of the anticipated settlement has occurred, the site will be released for the completion of site construction. We also recommend that at least one settlement monument in each of the two areas be installed in a cut/bedrock area to be used as a control to adjust /evaluate the survey data. Dewaterins Trench We had previously discussed the possibility of a dewatering trench in each area to accelerate the settlement process. Based on further review of the site conditions, these trenches may not be effective due to the potential caving and relatively low permeability of the alluvial soils. As such, the use of a dewatering trench is not recommended. If it is desired to reduce the overall settlement time, we recommend that deeper removals across the entire alluvial area be considered. In areas where remaining alluvium is less than 10 to 15 feet thick, it may be possible to remove all of the alluvial soils and thus eliminate the need for a settlement monitoring period. Proposed 1-1 /2 to 1 Cut Slopes We also understand that it is desirable to construct some of the onsite cut slopes at gradients of 1-1 /2 to 1 (horizontal to vertical) instead of 2:1. As noted in the project geotechnical report, this is acceptable from a geotechnical standpoint provided the slopes are constructed as geogrid reinforced slopes. A typical stability fill detail is included in the above referenced report. All stability fills should be provided with subdrains and benching in accordance with this detail. Stability fill backcuts should have gradients of not steeper than 0.75 to 1 (horizontal to vertical). The base of the stability fill should extend a minimum of 5 feet below the toe of slope. 1-1/2:1 slopes should be reinforced with geogrid reinforcement consisting of Tensar UX1400 or Miragrid 5T in accordance with the following: 980118-002 Slope Height (feet) up to 10 up to 20 up to 30 up to 40 up to 50 Grid Length at Top of Buttress (feet) 10 10 15 20 25 Grid Length at Bottom of Buttress (feet) 10 20 30 40 50 Average Vertical Grid Spacing (feet) 3 3 2.5 1.8 1.5 Actual design will be based on the actual design slope height and will be provided when the actual slope areas are identified. The backcut of all buttress fills should be mapped by the geotechnical consultant during grading to verify that conditions do not differ significantly from those used in our analyses. Thank you, for this opportunity to be of continued service. If you have any questions regarding this letter, please do not hesitate to contact this office. Respectfully submitted, LEIGHTON AND ASSOCIATES, INC. Michael Stewart, CEG 1349 Director of Geology Distribution: (2) Addressee FAX 760 931-0680 < Franzone, RCE 3 r of Engineering