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HomeMy WebLinkAboutSummary Geotech Due Diligence Review Jun.11, 2004 ~ 4.' ' '~• ~ .,., :::. ~ . I. ;::.' ; ~. 26590 Madison Avenue ~ r~~~i~Pi~ 2~'~ ~i %~z.~~~ Geotechnical • Coastal • Geologic • Environmental Murrieta, California 92562 • (909) 677-9651 June 11, 2004 FAX (909) 677-9301 W.O. 4379-A-SC KB Home Coastal, Inc. 26201 Ynez Road, Suite 104 Temecula, California 92591 Attention: Ms. Michelle Johnson Subject: Summary of Geotechnical Due Diligence Review of Documents, Temecula 79, Tract No. 25004, APNs 957-020-009-4, -010-4, -011-5, -013-7, -016-0, - 017-1, and 957-072-3, City of Temecula, County of Riverside, California Dear Ms. Johnson: In accordance with your request and authorization, GeoSoils, Inc. (GSI) has completed a review of the referenced geotechnical reports provided by your office on the subject property (see the Appendix). The purpose of our evaluation was to review site conditions and the referenced reports, relative to the proposed residential development, and to provide an opinion regarding the suitability of the site for the proposed development, based on our review. The scope of work for this evaluation includes a reconnaissance of the site to observe existing conditions, a review of the referenced supplemental geotechnical investigation by Geocon, Inc. (GI), and the referenced preliminary due diligence report by Jones Planning Consultants (JPC), evaluation of data, and preparation of this summary report. Subsurface studies were not conducted as part of this review. SITE DESCRIPTION AND PROPOSED DEVELOPMENT The irregular-rectangular shaped site, roughly ±33 undeveloped acres in area, is located on the south side of Murrieta Hot Springs Road, between Serarphina Road and Leon Road, and north of Andrews Way in the City of Temecula, Riverside County, California. Topographicaliy, the site consists of rolling hills wiih flat ridge tops and two drainages trending east-west in the central portion of the property. Elevations onsite range from approximately 1,235 feet Mean Sea Level (MSL) to 1,325 feet MSL. Overall, vegetation consists predominantly of grasses, weeds, brush, and trees. Drainage appears to be directed offsite to the west, via the drainages. Based upon our recent site reconnaissance, a concrete foundation is present in the central portion of the property and abundant trash/debris has been dumped on the property, as well as numerous stockpiles of soil. Fill has been placed in the drainages on the northern portion of the property in conjunction with the recent grading on properties to the east and west of the subject tract. 1 ~ ~ , A 170-foot wide north-south trending Metropolitan Water District (MWD) easement and a 30-footwide Southern California Edison (SCE) easement are located alongthe east portion of the property, and trend toward the center, in the northern portion of the site. Based upon our review of GI (2003) and a rough grading plan for Tract No. 25004 prepared by Medofer Engineering, Inc., dated April 28, 2004, future site development appears to consist of site preparation for the construction of a residential subdivision consisting of 79 single-family lots and associated infrastructure. Cuts and fills are anticipated to be on the order of 33 feet (Lots 69 and 70) and 30 feet (Lot 59), respectively, excluding remedial removals. Cut and fill slopes are on the order of 20 feet (Lot 7) and 30 feet (Chandler Drive and Suzi Lane), respectively, and are planned at gradients of 2:1 (horizontal to vertical [h:v]) or flatter. PREVIOUS WORK BY OTHERS Supplemental Geotechnical Investigation A supplemental geotechnical investigation of the site was completed in 2003 by GI (also referred to in this report as the "Consu ItanY'). This investigation presented the ConsultanYs findings from reconnaissance mapping, review of aerial photographs, subsurface exploration, laboratorytesting, and engineering analysis in GI's geotechnical report, dated July 2, 2003 (see the Appendix). Based on the Consultant's analysis, the proposed development was determined to be feasible from a geotechnicai standpoint, and recommendations were prepared and presented in GI (2003). Some of the salient conclusions and recommendations presented in GI (2003) are noted below for later discussion: • Undocumented artificial fills, up to 12 feet thick, were encountered in areas within the southern and central portions of the site. Fill associated with the MWD/SCE easement were observed in the eastern and north central portions of the property. One to three feet of topsoil covers most of the formational units (Pauba Formation and granitic bedrock) onsite. Alluvial deposits, up to approximately 15 feet in thickness, were encountered in the drainages and beneath portions of the undocumented artificial fill. The Pauba Formation was encountered in the higher elevations of the site and underlies the undocumented artificial fill and alluvium across a majority of the site. In the northern portion ofthe site, granitic bedrock was encountered at depths on the order of 4 to 5 feet below existing grade. Soil expansion testing indicates that soils onsite are generally low to medium expansive (Expansion Index [E.I.] less than 90). The sulfate exposure to concrete was determined to be negligible, per the Uniform Building Code ([UBC], International Conference of Building Officials [ICBO], 1997). KB Home Coastal, Inc. W.O. 4379-A-SC Temecula 79, Temecula June 11, 2004 Fle:e\wp9lmurr~rc4300\4379a.ddr Page 2 ~ GeoSoils, Inc. ~ ~ Groundwater was not encountered during the subsurface investigation onsite. Groundwater is anticipated to be at a depth of greater than 50 feet below existing grades across the site. The Consultant concluded that groundwater should not adversely affect site development, but did indicate that localized areas of perched groundwater may be present and seasonal fluctuations in the regional groundwater table may not be precluded. Sump pumps were recommended to mitigate any adverse groundwater conditions encountered during grading. Faulting was not noted onsite. The Consultant concluded thatthe site is not located within an "Alquist-Priolo Special Studies Zone." The Elsinore fault zone (i'emecula segment) is located about 4.5 miles to the west of the project site. The liquefaction potential for the site was evaluated. This evaluation determined that due to the lack of a shallow groundwater table, the presence of relatively dense formational materials (i.e., Pauba Formation and granitic bedrock) at relatively shallow depths, and the planned remedial grading, the potential for liquefaction at the site is very low. Existing fills and alluvium onsite were identified as being unsuitable for the support of structural loads, and ihus, will require removal and recompaction. Deep cuts are planned for lots and streets in the northern portion of the site which is underiain by granitic rock. Excavating difficulties are expected in this area and blasting should not be precluded. Based upon GSI's review of the rough grading plans for Tract No. 25004, dated April 28, 2004, cuts in granitic bedrock, up to 26 feet, are proposed in Lots 56, 57, and 58, as well as in Sandpiper Lane and Shree Road. A formal analysis of rock hardness (i.e., seismic lines, airtrack drilling) does not appear to be included. The Consultant provided recommendations for placement of oversize rock (greater than 12 inches in diameter). • A slope stability analysis was performed by the Consultant for 2:1 (h:v) slopes up to 40 feet high, utilizing remolded shear laboratory data from alluvial materials. Results indicated a factor of safety of 3.4 (unusually high). • The Consultant provided recommendations for both conveniional and post-tensioned foundation systems. Differential settlement design criteria was not provided. • Subdrain recommendations were provided by the Consultant for major drainage swales. • A grading plan review is recommended by the Consultant in order to verify that the plans are in accordance with the existing recommendations, and to determine the need for additional studies/sitework. KB Home Coastal, Inc. W.O. 4379-A-SC Temecula 79, Temecula June 11, 2004 Flle:e\wp9~murr~rc4300\4379a.ddr Page 3 ~ GeoSoils, Inc. ~ ~ Preliminary Due Diligence Report A preliminary due diligence of the site was completed in 2004 by JPC. The oniy geotechnical aspect presented in this report dealt with the deep cuts planned in granitic rock. JPC recommended overexcavation in the streets and pads to facilitate excavations for foundations and utilities. DISCUSSION AND COMMENT Based on our review, the following discussion and comments are offered. Additional comment and analysis by the Consultant of record will be necessary in order to respond to, and clarify some of the issues presented below. In general, GSI concludes the subject tentative tract was generally investigated inaccordance with current standards of practice; however, some conclusions and recommendations do not contain suificient data to support their validity. There were some differences between field techniques and the conclusions reached by GI (2003) and GSI's evaluation of site conditions. GSI is also unaware if the report by GI (2003) has been approved by the controlling authorities. GSI's conclusions and recommendations pertaining to these issues are presented below. Offsite Gradinq In the northern portion of the subject property, fill has been placed within the drainage swale during the recent grading on the properties located on the east and west sides of the subjecttract. During our recentsite reconnaissance, GSI observed a drainage culvert at the base of the fill slope. It is not known whether subdrains were installed beneath the fill. The as-built grading reports should be obtained for the tracts located east and west of the subject property for review. Subsequent to review of these reports, recommendations for subdrain installation on the subject property should be provided, as weli as for removals, benching, etc. into the existing fill, and/or mitigation. Rock Hardness Based upon our experience in the vicinity, in general, the granitic bedrock is rippable to approximately 5 to 10 feet below existing ground surface. Below this depth, it is likely very difficult to excavate. Based upon planned cuts up to approximately 26 feet deep, blasting cannot be precluded. Overexcavation of pads and utility inverts should be considered to facilitate construction of foundations and utility trenches, as well as mitigation of perched groundwater conditions that may occur after grading. For budgetary planning purposes, rock hardness studies should be considered. KB Home Coastal, Inc. W.O. 4379-A-SC Temecula 79, Temecula June 11, 2004 Flle:e\wp9lmurr~rc43D0\4379a.ddr Page 4 4 l GeoSoils, Inc. ~ Slope Stabilitv C~ Cut slopes on the order of 20 feet high are planned within the Pauba Formation. The Consultant did not provide information on structure (i.e., bedding and fractures). Based upon our experience in the vicinity, the Pauba Formation is relativelyflat lying and relatively high angle fractures exist in the granitic bedrock. As such, cut slopes to pianned heights should be stable, however, adverse conditions (i.e., out of slope bedding and/orfractures) should not be precluded as well as the need for stability/buttress fills. Additional slope stability analysis utilizing site specific shear test data should be performed. Perched Groundwater Potential In general and based upon the available data to date, groundwater is not expected to be a major factor in development of the site, assuming shallow excavations. However, the potential for seepage to develop along fill/bedrock contacts may impact design aspects, including subdrainage, cutoff barriers, and overexcavation bottom gradients. Perched groundwater conditions may not be precluded from occurring in the future, both during and after grading, from site irrigation, poor drainage, or damaged utilities, and should be anticipated. Additionally, the use of permanent sump pumps should be reconsidered, since they may not function if they have no power. Settlement Criteria and Foundation Desian GI (2003) did not provide a settlement evaluation so that design criteria for differentiaf settiement could be furnished. GI should provide the design values for differential settlement vs. ultimate fill thickness and corresponding foundation categories. GSI would like to point out that if the proposed deep fills are in areas of deep removals, it is possibie that the resultant fill could exceed 50 feet in thickness. Should this condition occur during grading, filis with an ultimate thickness greater than 50 feet should be monitored for settlement. Also, fills 50 feet thick or greater, should be placed at 95 percent relative compaction. These are generally accepted industry standards in Riverside County. Governina Agency Review/Approval The report(s) should be submitted to the governing agency, along with a 40-scale grading plan review, for approval. PRELIMINARY CONCLUSIONS AND RECOMMENDATIONS It is GSI's opinion that the project appears to be feasible from a geotechnical viewpoint. However, the Consultant's evaluations, rock hardness, slope stability, remedial earthwork, and settlement appear to need further justification. Further evaluation of some conditions noted above is recommended. Accordingly, the Consultant of record should respond to KB Home Coastal, Ine. W.O. 4379-A-SC Temecula 79, Temecula June 11, 2004 ~ Flle:e\wpsMurr~resi3oo\a37sa.ddr Page 5 GeoSoils, Inc. ~ ~ the requested information and/or comments so that our review can be completed and conclusions presented regarding the adequacy ofthe Consultant's recommendations and conclusions, in light of the data and analysis presented. Based on the above, it is recommended that budgetary planning consider the ramifications of the conditions noted. Additionally, GSI recommends that ali trash, debris, and waste materials be disposed of offsite, in accordance with current local, state and federal disposal regulations. Any materials containing petroleum residues encountered during property improvements should be evaluated prior to removal and disposal, following proper procedures. Any buried trash/debris encountered should be evaluated by an experienced environmental consultant prior to removal. Dumped stockpiled soils may be utilized as fill materials, providing any deleterious materials are removed and properly disposed of. LIMITATIONS GSI has performed the services for this project in accordance with the terms of a contract between GSI and the Client, and in accordance with current professional standards for investigations of this type. The conclusions presented in this report are based on the information collected during the study, the present understanding of the site conditions, and professional judgment. Piease note, subsurface conditions may vary from those provided in the document reviewed by GSI. The interpretations and recommendations of GSI are based solely on such information and/or information suppiied by Client. Findings of this investigation based on data provided by others carries no warranty, expressed or implied, as a result of the usage of such data.. It is possible that future investigations may reveal additional data or variations of the currsnt data which may require the current conclusions and recommendations to be reevaluated. As a result, GSI makes no warranty, either express or implied, as to its findings, opinions, recommendations, specifications, or professional advice except that they were promulgated after being prepared in accordance with generally accepted standards of care and diligence normally practiced by recognized consulting firms performing services of a similar nature. The information in this report is relevant to the date of the site work, and should not be relied on to represent conditions at any later date. Facts, conditions, and acceptable risk factors change with time, accordingly, this report should be viewed within this context. KB Home Coastal, Ine. W.O. 4379-A-SC Temecula 79, Temecula June 11, 2004 Flle:e\wp9Unurr~rc4300\4379a.ddr Page 6 ~ ~O.SOi1S~ InC. ~ ~ The opportunityto be of service is appreciated. If you have any questions pertaining to this report or any other matter, please do not hesitate to call us ai (909) 677-9651. ~._ Respectfully GeoSoils, Inc. P John P. Fr nkl Engineering Gi RGC/DG/JPF/DWS/jk Cr~\ :~~~~~ z ~ 1340 Attachmeni: Appendix - References Distribution: (4) Addressee DaVld W. ~Keu Civil Engineer, KB Home Coastal, Inc. W.O. 4379-A-SC Temecula 79, Temecula June 11, 2004 ~ Fle:e\~^~p9\murt1rc4300\4379a.ddr Page 7 . ~ GeoSoils, Inc. ~ • APPENDIX REFERENCES Envicom Corporation, 1976, Seismic safety and safety elements technical report for the County of Riverside and the Cities of Beaumont, Blythe, Coachella, Corona, Desert Hot Springs, Hemet, Indian Wells, Indio, Norco, Perris, Riverside, and San Jacinto. Geocon, Inc., 2003, Supplemental geotechnical investigation, tract no. 25004, Murrieta Hot Springs Road, Temecula, California, P.N. 20141-12-01, July 2. Hart, E.W., and Bryant, W.A., 1997, Fault-rupture hazard zones in California: California Division of Mines and Geology, Special Publication 42 (revised), 32 pp. International Conference of Building Official, 1997, Uniform building code. Jennings, C.W.,1994, Fault activity map of California and adjacent areas, scale 1:750,000, CDMG Map No. 6. Jones Planning Consultants, 2004, Preliminary due diligence, Temecula 79 (TM 25004), Temecula, California, May 20. Kennedy, 1977, California Division of Mines and Geology, 1977, Recency and character of faulting along the Elsinore fault zone in Southern Riverside County, California, Special Report 131. Norris, R.M., and Webb, R.W., 1990, Geology of California, second editions, John Wiley & Sons, Inc. 8 GeoSoils, Inc.