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Home My WebLink About20200717110955475S. E. Medall & Associates, lnc. — Consultants in the Earth Sciences 3010 SonIII flumly nnwv, I os AnoI,Iv- , Ca IIIfo((11,19006, E • ;' 1:11:190 1079 2 16 8 Soulh l lathaway t;trnr,l, Sanla Ana, GaIIIofnia 92105 • / 141646 0602 February 20, 1978 County of Los Angeles Department of the County Engineer Soils Engineering Section 550 South Vermont Los Angeles, California 90020 Attention: Mr. Charles F. Ruggles Subject: Response to Soils Engineering Section Review Sheet, dated February 6, 1978, Tracts 34160 and 34161, Parent Tract 29053), Diamond Bar Area, County of Los Angeles Reference: Report by S. E. Medall & Associates, Inc., dated December 19, 1977 Dear Mr. Ruggles: As discussed in our conversation of February 15, 1978, the following comments are presented relative to the remarks provided in the subject review sheet. For our cross sections, Y-Y and HH-HH, the county has indicated that according to these geologic cross sections, the bedding planes reverse directions beneath the buttress. The calculations for potential failure beneath the buttress key does not reflect this condition, please reanalyze. As discussed in our aforementioned conversation, these cross sections are two-dimensional representations of three- dimensional conditions that actually become more favorable in a down slope direction. When reviewing such two-dimensional E,,,NGHNJEER1NG GEOLOGY S PC TI County of Los Anyclos Page 2 February 20, 1978 cross sections, care must be taken not to misinterpret the geotechnical significance of apparent dip conditions. It is our opinion that our assumption of linear planar conditions is a very conservative approximation that does not warrant further refinement. The conservative nature of our evaluation of the Y-Y cross section should be further evident upon review of this cross section's orientation relative to the orientation of the proposed slope surface. The oblique angle of the slope in the cross section would suggest at most, a wedge type potential instability whereas our analyses assume the infinite slope condition. For our section Z-Z, the county has indicated that the calculations submitted using the Sultan -Seed method failed to recognize that the contact plane between the active and passive wedges traversed different soils. Shear values for the. stronger soils were used throughout. Using correct shear values, this section may not meet county standards. We recognize that it can be argued that since we utilized bedrock shear strengths through an area which actually contained bedrock and compacted fill, the assumption of S. E. Medall & Associates, Inc. County of Los Angeles February 20, 1978 Page 3 bedrock shear strength may not be a conservative assumption. In consideration, however, of the numerous compounding conservative assumptions that must be made to make such a three-dimensional stability evaluation statically determinant, it is our opinion that the assumption made was a reasonable assumption and the resulting design adequate. In consideration of the county's concern, however, we have re-evaluated the buttress requirements for the cross section. In order to establish static equilibrium in conformance with minimum county criteria, two feet was added to the previously recommended key depth. For cross section FF-FF, the county has indicated that according to this section, the outer shear key slope (lower slope) will exceed 12:1 horizontal to 1 vertical. This exceeds the minimum requirement of the county code and must be analyzed. on this cross section FF-FF, existing and proposed grading contours were indicated along with the corresponding geologic information underlying that area. The shear key requirement of this area was recognized upon review of this section and subsequently analyzed. Regrading of this slope for the S. E. Medall & Associates, Inc. County of Los Angeles Page 4 February 20, 1978 installation of the recommended shear key should be performed in accordance with the recommendations which accompany the referenced report. Therein, it is indicated that all cut and fill slopes proposed onsite should not exceed 11-2:1 (horizontal to vertical) slope ratio. It is hoped that the information contained herein is sufficient to satisfy the county's questions and concerns relative to the soils engineering information contained in the referenced report. Should the county have any further questions, however, please do not hesitate to call. Respectfully submitted, S. E. MEDALL & ASSOCIATES, INC. Gregory Axten, Director of Engineering Services GWA: j mb c: (3) Addressee 3) Weatherfield Homes Atten: Mr. Al Blunt Encl: Buttress Calculations - Section Z-Z1 S. E. Medall & Associates, Inc. a °'f r i ' i CIP7 5 = OP1 , 5,;5 1'2'5rQvm FS, 2c- S. E. Medal[ & Associates, Inc. Consultants in the Earth Sciences 3030 So. Bundy Er., L., An Bales, C.. 90066 (213) 390-4079 2168 So. Hathaway St., Santa An., Ca. 9270, (714) 546-6602 DATE BY W.O. SCALE 9, 05es I ' " 053uoj-d F, S' S. E. Medall & Associates, Inc. Consultants in the Earth Sciences 3030 So. Bundy Or,, Los Anget-, Ca. 90066, (213) 390-4079 2168 So. Hathaway St., Santa Ana, Co. 92705, (714) 546-6602 DATE r-_ I " I 'C' I I BY oSCALEW.O.