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Home My WebLink AboutCT 72-20; La Costa Vale Unit 3 Lot 473; Soils Report Peer Review Response; 1990-01-22RESPONSE TO GEOTECHNICAL PEER REVIEW (PROJECT PE 2.89:42) _- - - - - - - - - January 20, 1990 Project No. 8881297-04 Prepared For: CITY OF CARLSBAD Department of Engineering 2075 Las Palmas Drive Carlsbad, California 92009-4859 - 5421 AVENIDA ENCINAS, SUITE C, CARLSBAO, CALIFORNIA 92008 (619) 931-9953 FAX (619) 931-9326 - ,.- - ~- - - - - To: January 22, 1990 Project No. 8881297-04 City of Carlsbad Department of Engineering 2075 Las Palmas Drive Carlsbad, California 92008 Attention: Mr. Mike Boraks Subject: Response to Geotechnical Peer Review (Project PE 2.89:42) References: Leighton and Associates, Inc., 1989a, Preliminary Geotechnical Investigation, Proposed Single-Family Residence, Lot 473, La Costa Vale, Unit No. 3, Carlsbad, California, dated March 20, 1989 Leighton and Associates, Inc., 1989b, Revised Slope Stability Analysis, Proposed Barels Residence, Lot 473, Cadencia Street, Carlsbad, California, dated November 28, 1989 Provided herewith is our response to third party review comments by Owen Consultants dated January 12, 1990 for the subject project. For convenience, our comments are numerated to correspond with the review comments (attached). 1) The sample tested for shear strength was collected from the existing fill soils at the site and remolded to 90 percent relative compaction. The sample was screened of particles larger than a No. 4 sieve prior to sample preparation. A copy of the three-point direct shear test is attached in Appendix B. 2) Based on our evaluation of the site conditions, we feel that the shear result discussed above provides a conservative estimate of shear strength for fill and bedrock materials. The test procedure utilized does not account for the presence of angular rock found in the fill soils which would significantly raise the shear strength of the soil. - - 5421 AVENIDA ENCINAS, SUITE C, CARLSBAD, CALIFORNIA 92008 (619) 931-9953 FAX (619) 931-9326 8881297-04 - - -. -. - .~~~~ .- - - .,. - - -. 3) 4) The formational bedrock at the site consists of metavolcanic rockwhich cannot be tested for shear strength by conventional means. However, the shear test for the fill soils provides an extremely conservative estimate of the bedrock strength for the reasons cited above. The values for bearing capacity sliding friction and lateral earth pressure are typical values used in residential construction. The fill strength values utilized for stability analysis are considered applicable for soil bearing characteristics. However, utilizing these values results in much higher bearing capacity and allowable lateral earth pressures. In typical residential construction, loads are relatively light and use of these higher values may result in undersized foundation members. In addition, for this type of construction, settlement rather than bearing capacity governs the foundation design and use of a lower allowable bearing capacity helps reduce foundation settlement. Review of grading plans for Carlsbad Tract No. 72-20, La Costa Vale, Unit No. 3 by Rick Engineering indicates that the fill at the northwest corner of the lot was placed as part of the grading of Cadencia Street under the observation and testing of others. Based on pregrade topography, fill depths range from 0 to 7 feet. We recommend the condition of this fill be evaluated cl;;d;idgrading. Any areas of uncompacted or unsuitable fill should be Subgrade for roadways should be prepared as other areas to receive fill or structural improvements. R-value testing should be performed after subgrade preparation to provide representative sampling. This opportunity to be of service is appreciated. If you have any questions regarding our comments or require further clarification, please call at your earliest convenien Respectfully submitted, LEIGHTON AND ASSOCIATES, INC. , AL-- Stan Helenschmidt, GE 2064 (Exp. 6/30/92) Chief Engineer/Manager Attachments: Appendix A - Geotechnical Peer Review Appendix B - Shear Test Results and Bearing Capacity Calculations Distribution: (3) Addressee (1) Owen Consultants Attention: Mr. Martin Owen (1) Dr. Ron Barels (1) Mr. Rick Schleis -2- - - - - - - .- - ,‘r’;,.,i,~rh(,.,:.‘,, ‘,~ ;,l’,.,‘, #~ ‘,:;A:,,, _I_>, ,;i:: :,si ~;,; ,i 1: ‘LSF .,l>:.,+!:y, .,a’ ,,:,>,p -4.. it:,: January 12, 1990 Project No. 1037.1.1 City of Carlsbad Engineering Department 2075 Los Palmas Drive Carlsbad, California 92009-4859 Attention: Mr. Michael Boraks Assistant Civil Engineer Subject: GEOTECHNICAL PEER REVIEW FOR PE 2.89:42 Dear Mr. Boraks: In accordance with your request, we have performed a geotechnical peer review of the subject project. For our review we have been provided with the following: 1. “Preliminary Geotechnical Investigation, Proposed Single- Family Residence, Lot 473, La Costa Vale, Unit No. 3 (Tract Map No. 7950), Between Cadencia Street and Venado Drive, Carlsbad, California,” by Leighton and Associates, Inc., dated March 20, 1989. 2. “Revised Siope Stability Analysis, Proposed Barels Residence, Lot 473, Cadencia Street, Carlsbad, California,” by Leighton and Associates, Inc., dated November 28, 19S9. 3. “Grading Plan For: Cypress Abbey Company, Inc., 1982, Parliament Road, Encinitas, California 92024,” by Brian Smith Engineers, Inc., dated October 31, 19i39. OFrICES iN SAN ONFGO NP,,F?T”I ?‘v\C.~ “NC CONCORO, ‘c&rxN~a City of Carlsbad Engineering Department January 12, 1990 Page 2 - Our review indicates that the following items relating to the proposed 48 foot cut slope should be addressed or further evaluated by the consultant: 1. - - -~ - - Reference 2 indicates that soil property parameters for the slope stability analysis were obtained from direct shear tests on “remoided soil samples representative of site fill soils.” A description of the origin of these soil samples along with the applicable laboratory test data should be submitted. 2. In Reference 1, the consultant states that cut slopes will be excavated in the “massive metavolcanic bedrock” and the loose undocumented fill soils will be removed as part of slope grading. The consultant should clearly state why the given unit weights, cohesion and friction angle obtained from “site fill soils” are applicable to the analysis of the formational bedrock identified in the area of the cut slope. In addition to the above issues, we feel that the consultant should clarify the following items as they pertain to other aspects of the project. 3. Reference 1 indicates recommended design values for bearing capacity of 2,500 psf; lateral resistance of 300 psf per foot of depth; and a coefficient of friction of 0.30. The consultant should provide the results of shear tests or indicate any assumptions made which resulted in the selection of these values. - .- - - 4. Reference 1 states that structural development is currently not planned in the undocumented fill areas in the northwest comer of the property. The preliminary grading plans show a proposed driveway crossing this area and Reference 1 indicates that pavement design will be based on soil conditions after grading. We request that applicable recommendations for subgrade preparation and road improvements be made prior to site grading. - QIYi)(CCNSULTANTS - - City of Carlsbad Engineering Department January 12, 1990 Page, 3 This opportunity to be of service is appreciated. If you have any questions, - please call. - - - RMF/MRO:ms Copies: (2) Addressee - -. NoRMK8TRs8.w AV@TO@O Moirturo Contww SampI Location Symbol setor. After Frktkn An@ Cohodora Romarkr T-5 0 @ 0.5-2' 0 13.1 29" 240 - Projoet No. 8881297-04 DIRECT SHEAR TEST RESULTS Project Name Barels - ht. 1/2_2/90- Fiouro No. B-1 ~ 3016 matt - - - - - - - - - - .-- - _- - .- -. .- - 8881297-04 BEARING CAPACITY CALCULATIONS FOR BARELS RESIDENCE * = 29’ N = 20.5 B = 1’ c = 240 psf Nq = 34.8 D = 1’ y = 120 N; = 17.7 Q IJtt =cN,tqN,+ tY NY = 240(34.8)+ 120(1)(20.5)+ t(120)(17.7) = 11,874 psf Q all =&= [3,958psf1 3 tan* = 0.55 p = 2/3 tanr = 10.36 op = qtan' (45+$/2)+ 2c tan (45+r/2) = 120d tan' (45+29/2)+ 2(240) tan (45+29/2) 1 on = [346d t 8151 psf j B-2