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Home My WebLink AboutCDP 2022-0019; HOM RESIDENCE; GLOBAL SLOPE STABILITY EVALUATION; 2022-03-04GLOBAL SLOPE STABILITY EVALUATION HOM PROPERTY 2170 TWAIN AVENUE CARLSBAD, CALIFORNIA PREPARED FOR MR. ROBERT HOM CARLSBAD, CALIFORNIA MARCH 4, 2022 PROJECT NO. G2826-32-01 CDP2022-0019 Project No. G2826-32-01 March 4, 2022 Mr. Robert Hom 2170 Twain Avenue Carlsbad, California 92008 Subject: GLOBAL SLOPE STABILITY EVALUATION HOM PROPERTY 2170 TWAIN AVENUE CARLSBAD, CALIFORNIA Dear Mr. Hom: In accordance with your request, we have performed a stability analysis of the rear yard slope located along the western margin of the subject property. The purpose of our study was to evaluate the global stability of a slope configuration that was created during rear yard retaining wall improvements constructed on the property. The scope of our work did not include an evaluation of internal retaining wall stability or the suitability of other hardscape improvements. We have no opinion in that regard. The subject property is Lot No. 68 of Carlsbad Tract 97-16A (Kelly Core) and was graded in 2003. Geocon Incorporated provided geotechnical services during project development. The applicable geotechnical report is entitled Final Report of Testing and Observation Services During Site Grading, Kelly Core; CT97-16A, Single Family Lot Nos. 1 through 76 and 84 through 155, Carlsbad, California, prepared by Geocon Incorporated, dated March 3, 2003. A review of the report indicates that the subject property is a cut lot underlain by natural Terrace Deposits. The soils consist of fine to medium grained silty sand. The slope excavation along the west margin of the lot was originally graded at a ratio of 2:1 (horizontal:vertical) with a 5-foot-high retaining wall at the base. The total slope height is approximately 25 feet. In 2021, the slope was modified by construction of a series of stepped Mechanically Stabilized Earth (MSE) retaining walls to create level terraces. A stairway and observation deck were also constructed as part of the rear yard improvements. A topographic survey of the new configuration was prepared by O’Day Consultants. We generated four cross-sections based on the survey for the purpose of evaluating global slope stability. The locations of Cross-Sections A-A’, B-B’, C-C’ and D-D’are shown on the Site Plan, Figure 1. The cross sections and output files that show the calculated factor of safety for each section is presented on Figures 2 through 5. The computer program SLOPE/W distributed by Geo-Slope International was utilized to perform the slope stability analyses. This program uses conventional slope stability equations and a two- dimensional limit-equilibrium method to calculate the factor of safety against deep-seated failure. For our analysis, Spencer’s Method was used. Spencer’s Method satisfies both moment and force GEOCON INCORPORATED GEO TE C HNI CAL ■ ENVIRONMENTAL ■ MATERIALS O 6960 Flanders Drive ■ San Diego, California 92121-2974 ■ Telephone 858.558.6900 ■ Fax 858.558.6159 Project No. G2826-32-01 - 2 - March 4, 2022 equilibrium. The soil strength parameters for the Terrace Deposits used in our analysis were derived from laboratory testing during the initial site investigation and our studies performed nearby. Based on the results of the global slope stability analyses, a minimum static factor of safety of at least 1.5 is present along each cross section analyzed. With respect to the potential for soil erosion, the hillside has been generally terraced with walls and flat planter surfaces. As a result, the exposure of potentially erosive soils has been reduced compared to the originally graded slope. Therefore, we conclude that the conditions are more favorable now compared to the 2:1 graded slope with respect to surficial soil erosion. As previously noted, our evaluation did not consider the stability of the MSE retaining walls and their zone of influence. We have no opinion in that regard. With that said, it is our opinion that the slope is grossly stable with respect to the potential for deep-seated failure. If there are any questions regarding this correspondence, or if we may be of further service, please contact the undersigned at your convenience. Very truly yours, GEOCON INCORPORATED Trevor E. Myers RCE 63773 David B. Evans CEG 1860 TEM:DBE:am (e-mail) Addressee A A'B' B C C' D' D 6960 FLANDERS DRIVE - SAN DIEGO, CALIFORNIA 92121 - 2974 PHONE 858 558-6900 - FAX 858 558-6159 SHEET OF PROJECT NO. SCALE DATE FIGURE Plotted:03/03/2022 2:52PM | By:RUBEN AGUILAR | File Location:Y:\PROJECTS\G2826-32-01 Hom Property\SHEETS\G2826-32-01 SitePlan.dwg GEOTECHNICAL ENVIRONMENTAL MATERIALS 1" = SI8E PLAN HOM PROPERTY CARLSBAD, CALIFORNIA 5'03 - 04 - 2022 G2826 - 32 - 01 1 1 1 GEOCON LEGEND ........APPROX. LOCATION OF CROSS-SECTION D D' 2.5 Distance (ft) -10-8-6-4-2024681012141618202224262830323436384042444648505254565860 320 322 324 326 328 330 332 334 336 338 340 342 344 346 348 350 352 354 El e v a t i o n ( M S L ) 320 322 324 326 328 330 332 334 336 338 340 342 344 346 348 350 352 354A A' Hom Property Project No. G2826-32-01 Section A-A' Name: AAc0.gsz Date: 11/18/2021 Time: 10:21:13 AM Color Name Unit Weight (pcf) Cohesion' (psf) Phi' (°) Qt - Terrace Deposits 125 300 30 Existing Condition Static Analysis Qt Figure 2 2.4 Distance (ft) -10-8-6-4-2024681012141618202224262830323436384042444648505254565860 320 322 324 326 328 330 332 334 336 338 340 342 344 346 348 350 352 354 El e v a t i o n ( M S L ) 320 322 324 326 328 330 332 334 336 338 340 342 344 346 348 350 352 354B B' Hom Property Project No. G2826-32-01 Section B-B' Name: BBc0.gsz Date: 11/18/2021 Time: 10:24:12 AM Color Name Unit Weight (pcf) Cohesion' (psf) Phi' (°) Qt - Terrace Deposits 125 300 30 Existing Condition Static Analysis Qt Figure 3 2.3 Distance (ft) -10-8-6-4-2024681012141618202224262830323436384042444648505254565860 320 322 324 326 328 330 332 334 336 338 340 342 344 346 348 350 352 354 El e v a t i o n ( M S L ) 320 322 324 326 328 330 332 334 336 338 340 342 344 346 348 350 352 354C C' Hom Property Project No. G2826-32-01 Section A-A' Name: CCc0.gsz Date: 11/18/2021 Time: 10:25:26 AM Color Name Unit Weight (pcf) Cohesion' (psf) Phi' (°) Qt - Terrace Deposits 125 300 30 Existing Condition Static Analysis Qt Figure 4 1.9 Distance (ft) -10-8-6-4-2024681012141618202224262830323436384042444648505254565860 314 316 318 320 322 324 326 328 330 332 334 336 338 340 342 344 346 348 350 352 354 El e v a t i o n ( M S L ) 314 316 318 320 322 324 326 328 330 332 334 336 338 340 342 344 346 348 350 352 354D D' Hom Property Project No. G2826-32-01 Section D-D' Name: DDc0.gsz Date: 11/18/2021 Time: 10:27:11 AM Color Name Unit Weight (pcf) Cohesion' (psf) Phi' (°) Qt - Terrace Deposits 125 300 30 Existing Condition Static Analysis Qt Pool Figure 5