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HomeMy WebLinkAboutCDP 2020-0026; BEGONIA COURT RETAINING WALL; RESPONSE TO THIRD-PARTY GEOTECHNICAL REVIEW AND SUPPLEMENTAL GEOTECHNICAL INVESTIGATION OF SLOPE REPAIR; 2020-11-18- RECORD COPY To: Mr. David Rick Martin R. Owen PE, GE 4596 Mount Hubbard Avenue, San Diego, CA 92117 Phone /Text: 619-813-8462 Email: martinowen@geotechenglneer.com City of Carlsbad, Land Development Engineering 1635 Faraday Avenue Carlsbad, California 92008 DclL lnitJaJ Job No. 200506 November 18, 2020 Subject: Response to Third-Party Geotechnical Review and Supplemental Geotechnical Investigation of Slope Failure 2210 Plaza Bonita Carlsbad, California 92009 Project ID: PD2020-0036 References: • Geotechnical Inspection of Slope Failure, 2210 Plaza Bonita, Carlsbad, California 92009, by Martin R. Owen PE, GE, dated June 1, 2020 • Cut/Fill Quantity for Repair of Slope Failure, 2210 Plaza Bonita, Carlsbad, California 92009, by Martin R. Owen PE, GE, dated September 22, 2020 • Grading Plans for Slope Repair, 2210 Plaza Bonita, by The Sea Bright Company, dated· October 5, 2020 (Sheets 1 through 4) • Third-Party Geotechnical Review (First), Slope Failure, 2210 Plaza Bonita, Carlsbad, California 92009, Project ID: PD2020-0036, by Hetherington Engineering, Inc., dated October 29, 2020, Project No. 9236.1, Log No. 21188 Dear Mr. Rick: Please find herein my response to the third-party geotechnical review issues listed in the review letter by Hetherington Engineering, Inc. referenced above. I have also conducted a supplemental geotechnical investigation, which is presented at the end of this response. My previous geotechnical inspection report, referenced above has been modified where necessary to reflect the response. Stephen E. Jacobs, CEG, Engineering Geologist contributed to the supplemental investigation and report. '2-/2 'I h.o n~t~ RECEIVED NOV 2 4 2020 LAND DEVELOPMENT ENG1NEER/NG Response to Third-Party Geotechnical Review and Supplemental Geotechnical Investigation of Slope Failure 2210 Plaza Bonita Carlsbad, CA 92009 RESPONSE TO HETHERINGTON REVIEW ISSUES Page2 Job No. 200506 November 18, 2020 Issue #1 -The Consultant should review the project grading plan, provide any additional geotechnical recommendations considered necessary, and confirm that the plans have been prepared in accordance with the geotechnical recommendations provided in the referenced report. Response : I have reviewed the project grading plan prepared by Bob Sukup, PE and confirmed that the plan has been prepared in accordance with the geotechnical recommendations provided in the referenced report, dated June 1, 2020. Issue #2 -The Consultant should provide an updated geotechnical map/plot plan utilizing the latest grading plan for the project to clearly show (at a minimum), a) existing site topography, b) proposed finished grades, c) locations of the subsurface exploration, d) geologic contacts, and e) remedial grading limits, etc. Response: I have provided an updated plot plan and geotechnical map and a grading plan and geotechnical map presented herein as Figures 2A and 2B, respectively. These maps show the existing site topography, proposed finished grades, locations of exploratory test pits, geologic contacts, and limits of proposed remedial grading on Figure 2A. Issue #3 -The Consultant should provide geologic cross-sections utilizing the current grading plan to clearly show (at a minimum), a) existing site topography, b) proposed finished grades, c) geologic contacts, d) geologic structure, e) locations of the subsurface exploration, f) temporary construction slopes, and g) remedial grading, etc. Response: I have provided two geologic cross-sections utilizing the current grading plan presented herein as Figures 4 and 5. These cross sections show the existing site topography, proposed finished grades, geologic contacts, geologic structure, locations of the exploratory test pits, temporary construction slopes, and limits of proposed remedial grading, Issue #4 -The Consultant should perform field exploration, laboratory testing, and analyses to provide a basis for the slope repair recommendations. Response: I performed site observations of the slope failure area and four exploratory test pits, laboratory testing, and analyses to support the slope repair recommendations. Issue #5 -The Consultant should provide recommendations for temporary excavations. Martin R. Owen PE, GE Geotechnical Engineer Response to Third-Party Geotechnical Review and Supplemental Geotechnical Investigation of Slope Failure 2210 Plaza Bonita Carlsbad, CA 92009 Page3 Job No. 200506 November 18, 2020 Response: Recommendations for temporary excavations shown on the two geologic cross sections A-A' and B-B' (Figures 4 and 5, respectively) are presented on Figure 7-Slope Repair. Issue #6 -The Consultant should address the surficial stability of the proposed repair slope. Response: The proposed repair slope should be surficially stable (FS greater than 1.5) provided the recommendations presented herein are implemented. Issue #7 -The Consultant should provide a statement regarding the impact of the proposed grading on adjacent properties and improvements. Response: The proposed remedial grading of the failed slope should have a minimal impact on the adjacent properties and improvements. Issue #8 -The Consultant should provide a list of recommended observation and testing during site grading and construction. Response: The recommended observation and testing during site grading and construction will include observations and testing of the slope excavation, filling and compaction. Observation and testing services will be provided by East County Soil Consultation & Engineering, Inc., 619- 258-7901. Issue #9 -The Consultant should provide a list of published maps/reports used in the preparation of the report. Response: I have provided a list of published and unpublished maps/reports used in the preparation of this report. This list is presented at the end of this report. SUPPLEMENTAL GEOTECHNICAL INVESTIGATION In accordance with the letter of third-party geotechnical review dated October 29, 2020 prepared by Hetherington Engineering, Inc., I have conducted a supplemental geotechnical investigation for the proposed slope repair to be constructed on the west-facing slope adjacent to the lot at 2210 Plaza Bonita, Carlsbad, California. My preliminary findings indicate that the site has several geotechnical-related issues that will impact project development. I provide herein my assessment of site conditions and recommendations for the proposed remedial grading of the failed slope. This assessment is subject to change as new data is developed. The scope of work performed for this supplemental investigation was as follows: Martin R. Owen PE, GE Geotechnical Engineer Response to Third-Party Geotechnical Review and Supplemental Geotechnical Investigation of Slope Failure 2210 Plaza Bonita Carlsbad, CA 92009 • Review of available grading and slope repair plans. Page4 Job No. 200506 November 18, 2020 • Review of available geologic literature and geotechnical reports associated with the tract development. • Subsurface soil exploration and laboratory soil testing. • Geotechnical analysis and preparation of my response to the third-party review and supplemental geotechnical investigation report summarizing my findings and conclusions. SITE AND PROJECT DESCRIPTION The subject slope is a steep (approximately 1½:1 H:V) west-facing, graded fill slope, about 15 feet high, that descends from t he west side of the subject residence down to a lower level an d swimming pool. The residence (labeled Building #8 on the grading plan, Figure 2B) is the westerly unit of a two- story, multi-unit town home building constructed in 1971. The building is {mostly) supported on conventional shallow footings and has lower level slab-on-grade floors. However, you indicated that the subject residence previously experienced foundation settlement and was stabilized by underpinning with pipe piles or other deep foundations. The date and extent of the foundation repairs are not known. You also indicated you recently inspected the interior of the residence and no building damage was observed. In addition, your insurance company sent an engineer to inspect the building and no damage was reported. Slope vegetation is moderate to good and consists of several shrubs and ivy and other ground cover. Reportedly, there was a recent leak in a sprinkler line near the top of the slope. It is not known how long the pipe was leaking. The leak is believed to be factor in the slope failure. Reportedly, also, there was a rupture of the sewer line, currently exposed on the back cut near the toe of the slope; the sewer line was reportedly repaired. I have previously listed my observations regarding the slope failure in the above-referenced report dated June 1, 2020. SUBSURFACE SOIL EXPLORATION A subsurface soil exploration was conducted on November 12, 2020 and consisted of hand excavating four test pits on the slope. The approximate locations of the test pits are shown on the attached Figures 2A and 2B. The logs of the test pits are presented on the attached Figure Martin R. Owen PE, GE Geotechnical Engineer Response to Third-Party Geotechnical Review and Supplemental Geotechnical Page 5 Investigation of Slope Failure 2210 Plaza Bonita Job No. 200506 Carlsbad, CA 92009 November 18, 2020 3. Two cross-sections through the subject slope are provided as Figures 4 and 5. The test pits were excavated to a depth of approximately 2 feet. The test pits were excavated and logged by Stephen E. Jacobs, CEG, Engineering Geologist SUBSURFACE SOIL CONDITIONS The area of the slope failure is underlain by a relatively thin layer of the recent landslide deposit, underlain by undocumented artificial fill, in turn underlain, at unknown depths, by sedimentary bedrock that is mapped by Tan and Kennedy (1996) and Kennedy and Tan (2007) as the Eocene age Santiago Formation (Figures 2A, 28 and 6). Tan and Kennedy (1996) described the Santiago Formation as "Light-colored, poorly-bedded, poorly-indurated, fine-to medium-grained sandstone interbedded with landslide-prone siltstone and claystone." Materials of the Santiago Formation were not encountered in our exploratory test pits. The attached test pit logs (Figure 3) should be referenced for a complete description of the materials encountered. A brief description of these units is described in order of increasing age. Landslide Deposit (Qal): Disturbed fill soils of the landslide deposit involved in the slope failure were observed in Test Pits 1 and 2, and in the temporary back cut near the toe of the slope failure. The landslide deposit extends from a thickness of approximately 1 foot just below the head scarp to approximately 2 feet at the top of the temporary back cut near the toe of the slope. The landslide deposit encountered consists of dark brown and olive gray, slightly moist to moist, soft, clayey sand and clayey silt with numerous angular clayey siltstone rock fragments. This material will require removal and recompaction in the area of the proposed remedial grading of the slope failure. Published geologic maps by Tan and Giffen (1995), Tan and Kennedy (1996) and Kennedy and Tan (2007) reported no ancient landslides in the vicinity of the subject site. Artificial Fill (Qaf): Undocumented fill was observed in all four exploratory excavations and in the temporary back cut near the toe of the failed slope. The fill soils encountered consist of medium to dark olive gray and brown, moist to very moist, firm to stiff, sandy clay, clayey silt and silty clay. The upper approximately 1 to 2 feet of fill soils exposed in the temporary back cut near the slope toe were observed to have numerous desiccation cracks. Martin R. Owen PE, GE Geotechnical Engineer Response to Third-Party Geotechnical Review and Supplemental Geotechnical Page 6 Investigation of Slope Failure 2210 Plaza Bonita Job No. 200506 Carlsbad, CA 92009 November 18, 2020 GEOLOGIC STRUCTURE AND BEDDING Regional bedding within the Santiago Formation is not mapped by Tan and Kennedy (1996) and Kennedy and Tan (2007) within the immediate vicinity of the subject site. The nearest mapped bedding attitudes from Tan and Kennedy (1996, Figure 6) show dips of 5 degrees to the west- northwest; this bedding dip angle is projected onto the geologic cross sections on Figures 4-5. GROUNDWATER Groundwater was not encountered in the exploratory test pits. However perched groundwater may develop on the subject slope due to landscape irrigation and excessively heavy rainfall. CONCLUSIONS Base on the findings of this supplemental geotechnical investigation, the following conclusions have been developed: • The landslide deposit appears to range from approximately 1 to 2 feet in thickness in the area of the slope failure. The landslide occurred in undocumented artificial fill. Possible removal depths are provided on the attached Figure 4, Geologic Cross Section A-A', and Figure 5, Geologic Cross Section B-B'. • The primary cause of the slope failure appears to be saturation of the slope soils and loss of shear strength resulting from a combination of recent heavy rainfall and a leaking sprinkler pipe and/or a leaking sewer pipe. • The steep slope and poor slope fill compaction appear to be other factors in the failure. • The slope failure is shallow and relatively minor and the subject residence does not appear to have been damaged or threatened by the failure. RECOMMENDATIONS • The slope failure should be repaired and the slope restored to its original grade and configuration, as follows: • The slope can be repaired using small grading equipment or hand equipment. • The existing slope vegetation within the slope restoration area should be entirely removed. Some of the shrubs may be salvageable and can be reused. Martin R. Owen PE, GE Geotechntcal Engineer Response to Third-Party Geotechnical Review and Supplemental Geotechnical Page 7 Investigation of Slope Failure 2210 Plaza Bonita Job No. 200506 Carlsbad, CA 92009 November 18, 2020 • The accumulated soils at the bottom of the slope should be removed and temporarily stockpiled on the nearby sidewalk or other area. • In addition, prior to placing fill, a 5-feet wide minimum (measured into slope) fill key, at least 2 feet deep, should be excavated at the bottom of the slope (see attached Figure 7). • As grading proceeds to the north, where there has been less slope displacement, it may be possible to excavate the fill key further up the slope (instead of at the bottom). • The onsite soils may be reused as fill, provided they are free of organics and debris and rocks and cobbles over 6 inches in dimension. Any import fill soils should be approved by the undersigned or other soil testing company. It is understood that East County Soils will be performing the fill compaction testing and grading observation. • Fill soils should be placed and compacted in 6 to 8 inches thick lifts/layers starting at the bottom of the fill key and working upwards. The fill should be moistened or dried as necessary to slightly above optimum moisture conditions and compacted by mechanical means to at least 90 percent relative compaction based on ASTM D 1557. • The 5-feet wide minimum fill width should be maintained as the fill is brought up. The fill should be benched into the original slope soils in 2 feet minimum, vertical benches (see attached Figure 7). • The upper portion of the slope should be overbuilt and cut back, or compacted by other means. • Horizontal layers of geogrid should be installed at 4 feet maximum vertical increments to provide extra strength. • The slope grading and compaction and placement of geogrid should be observed and tested as necessary by the undersigned or other soil testing company. SLOPE LANDSCAPING The slope should be re-landscaped with shrubs and deep-rooted ground cover such as ivy. Moderate irrigation will be required to establish the landscaping. Martin R. Owen PE, GE Geotechnical Engineer Response to Third-Party Geotechnical Review and Supplemental Geotechnical Investigation of Slope Failure 2210 Plaza Bonita Carlsbad, CA 92009 LIMITATIONS Page8 Job No. 200506 November 18, 2020 The conclusions and recommendations presented in this report may be modified as necessary during additional investigation and/or construction and are subject to field conditions. If significant modifications are made to the slope repair plans, revision of this report may also be necessary. This investigation is not to be considered a complete review of the geotechnical conditions, nor an investigation of latent conditions that have not manifested damage to date. The above conclusions and recommendations are based on my inspection, limited subsurface exploration, and experience with other, similar properties in San Diego County. This report provides no warranty, either expressed or implied, concerning future building or slope performance. Future damage from geotechnical or other causes is a possibility. This opportunity to be of service is appreciated. If you have any questions, please do not hesitate to call or contact me. Very truly yours, Martin R. Owen PE, GE Geotechnical Engineer Stephen E. Jacobs, PG, CEG Engineering Geologist Martin R . Owen PE, GE Geotechntcal Engineer Response to Third-Party Geotechnical Review and Supplemental Geotechnical Page 9 Investigation of Slope Failure 2210 Plaza Bonita Job No. 200506 Carlsbad, CA 92009 November 18, 2020 ATTACHMENTS: • References • Figure 1-Site Location Map • Figure 2A -Plot Plan and Geotechnical Map • Figure 2B -Grading Plan and Geotechnical Map • Figure 3 -Test Pit Logs (TP-1 through TP-4) • Figure 4 -Cross Section A-A' • Figure 5 -Cross Section B-B' • Figure 6-Regional Geologic Map • Figure 7 -Slope Repair LIST OF PUBLISHED MAPS/REPORTS USED IN THE PREPARATION OF THIS REPORT: County of San Diego, 1960, Topographic Survey, Sheet 338-1689, scale: 1" = 200'. County of San Diego, 1969, Grading Plans for Subdivision of Lot No. 227, La Costa Valley Unit No. 4, Map No. 5781, 2 sheets. County of San Diego, 1976, Topographic Survey, Sheet 338-1689, scale: 1" = 200'. Kennedy, M.P., and Tan, S.S., 2007, Geologic Map of the Oceanside 30' x 60' Quadrangle, Cal ifornia: California Geologic Survey, Regional Geologic Map Series, Map 2, scale 1:100,000. Soil Engineering Construction, 1989, Geotechnical Consultation for Remedial Repairs and Stabilization Revised, La Costa Village Condominiums, La Costa, California, Exhibit G, dated August 14, 1989. Solid Rock Engineering, Inc., 2007, Limited Phase I Geotechnical Engineering Evaluation for 2208 and 2212 Plaza De Las Flores, Updated to Include 2202, 2204, 2206, 2210, and 2214 Plaza De Las Flores, La Costa Village Condominium Complex, Carlsbad, California 92009, Project No. 61000268-03, dated June 22, 2007. Solid Rock Engineering, Inc., 2007, Limited Geotechnical Engineering Evaluation Report for La Costa Village Phase II Evaluation Project, 2208 and 2212 Plaza De Las Flores, Carlsbad, California 92009, Project No. 61000268-02, dated August 31, 2007. Martin R. Owen PE, GE Geotechnfccd Bngt.neer Response to Third-Party Geotecbnical Review and Supplemental Geotechnical Page 10 Investigation of Slope Failure 2210 Plaza Bonita Job No. 200506 Carlsbad, CA 92009 November 18, 2020 LIST OF PUBLISHED MAPS/REPORTS (CONTINUED): Tan, S.S. and Giffen, D.G, 1995, Landslide Hazards in the Northern Part of the San Diego Metropolitan Area, San Diego County, California, Landslide Hazard Identification Map No. 35: California Division Mines and Geology Open File Report 95-04, pp. 1-6, Plate 35D, Encinitas Quadrangle, scale 1:24,000. Tan, S.S., and Kennedy, M.P., 1996, Geologic Maps of the Northwestern Part of San Diego County, California: California Division of Mines and Geology Open File Report 96-02, Plate 2-Geologic Maps of the Encinitas and Rancho Santa Fe 7.5' Quadrangles, scale 1:24,000. The Sea Bright Company, 2020, Grading Plans for Plaza Bonita Slope Repair (2210 Plaza Bonita), City of Carlsbad, Sheet 4, scale: 1" = 20', dated October 5, 2020. Martin R. Owen PE, GE Geotechnical Engineer Response to Third-Party Geotechnical Review and Supplemental Geotechnical Investigation of Slope Failure 2210 Plaza Bonita Carlsbad, CA 92009 !ead· P ,;m I( tc,.~ C r.epo'iS lurJry .. ..!!, CnelT'M la Cc ... ...;.,, r-'ted S:ates Pesta-118 ~. Ser.•<:e ',;;;., -vors Avic1ra Pkwy FIGURE 1 SITE LOCATION MAP ,,, -.;.;.',g r :e e· siro Alga ~d .... ~ .§ ,.. :' ~ ' 2210 Plaza Bonita. Carlsbad, CA 92009 Alicanr~ Rd ,ii Page 11 Job No. 200506 November 18, 2020 RANCftO LA COSTA -n Pasta ,n !!, t . \ C Martin R. Owen PE, GE Geotechntcal Engtneer I [ B -E - ~· Exl)iananon: Cla :: Lanaslkle ooposn (Latest HOIOCOllO) 0.f = Att!OclaJ FUI ( Lal!! HolOOOllO) Tu = Santiago Formation (Eocene) .. --. .... -,. ... Approximate goologle contact Top OJ scarp Of CUI TOSI pll • Exposed sewer pipe u · Gootogtc cross soctton Approx. umns or proposoo remedial gsa<llng nos: UM n paronmesos ana aJICs 1s concealOd. AU tocauons are pproxlmato. I ..., r I ._,. __ P!~s. ,t,,:~c l'OOI- 10 Dua mnp laan frcm Gr.uing Pl1n11, fer P1.u-a 9a,uh•· SklpO ,.., (2210 Plaz.> Dor,~1 C..y cl C..i!sbod, p,opo,od by Tho, Soa 1tC"""'"'1)' SNoot•, "°•I~. t• 0 20', d>lodO<too«6.2020. ~ rm:) I\\ 1 L/1, ti ~\ ~ '=--,,,. . 1{ 111~ ' r---l--~ I 2210 1 \ I ft.,\ .. ,i,. . _1io-1n, _ :: A I ;lo I ?.7 I --~, I I 0 a: !<l. I': 7.0' 2. '7 7 CONNU:l'T 1 r ~-~";i~!~ ::, A ,t' f f( • USL J\.»);flt-l l,r, ~s• c,,r (t.4' 8~ .,., ol' :!\,Cl'<. t I n Cltffi.ff IIC1'< ----DilAIN l~l-21 I D~C.K M,EA L NoTt;: If n CAA g~,~~ • "1'~ -1'1 Pl~ HA"SlS 'I; ~MM.I> FlitlM 1/sE,. -'T• • 1'll~ fl ~SN',' AALt c.0.1 ·o 1lE. c.of4Nl!C-Teb '26 ~ ,').1~T\l.lv ' ,.s: I 3(.0f€. \j ~S-lloU>10(~) ---_ C-$"10~. , • N~; ~o ~~-.·~~ ~ 6~Ac. f,V--OIAII.J fll\a J. t-\At<E. SUP.~ 1W,;~ IS PO'S l'TIV~ 17IUIINA.C..t. -ro-rl-\6 l{i:.•Jl O~A\tl Ai 7'"Ei0P or= SLO~e,. ~ ll--l(',.c.. ; NO uJA~ IC. IS TO ORAIII O'leJZ "'™€ TOP OF '5l-0Pe. Z.. 11AY-t:. 'i:UP-',. -ro ~Ave'. A. fO~IT\'llb ORAl»AG~ c.au:;.-:;e. A• 'Ti,IE. ,Ola OJ:' SLO~ Al.ONG ·ntE P.c.,.t c.t, ~ ~Cl If 0'2AlllS TO lr\t G~IS1/NG /Nl..-ET ,,__ ____ _ L'"l N -::0 e:N =m -"""~!II !II =a"CI c:r "Cl 0 Ill -(IIQ = .?-t111~ ~ Ill g.,... ==0 \0 0 0 ;1 N = ..., gEfr:a ::;-\0 0 Q. ""O "Cl I m .,, r-a.a 0 --I C ~ "'m ""O m 0 Ii §; g. = -z g - RO -n ;' -s ~ ~ m ~ m C Ill 0 = ::a Q. -I m II) m C N "Cl n "Cl l> -:c m a z m = -S' n - l> ~ r-l s: e. l> 9. ""O I z ~ ~ -a o c:r c:r ~ z ... 0 """ . 0) N .,, • 0 Ill NQ QQ 0 U1 ~ N Q """ QQ'I N Re s p o n s e to Th i r d - P a r t y Ge o t e c h n i c a l Re v i e w an d Su p p l e m e n t a l Ge o t e c h n i c a l In v e s t i g a t i o n of Sl o p e Fa i l u r e 22 1 0 Pl a z a Bo n i t a Ca r l s b a d , CA 92 0 0 9 FI G U R E 2B Pa g e 13 Jo b No . 200 5 0 6 No vem b e r 18, 20 2 0 GR A D I N G PL A N & GE O T E C H N I C A L MA P Ge o t e c h n i c a l En g i n e e r Response to Third-Party Geotechnical Review and Supplemental Geotechnical Investigation of Slope Failure 2210 Plaza Bonita Carlsbad, CA 92009 Depth Feet 0 -1 1 -2 Depth Feet FIGURE 3 TEST PIT LOGS by Stephen E. Jacobs, CEG TEST PIT TP-1 Soil Description Landslide Deposit (Fill): Clayey Sand (SC). fine-to medium-grained, brown, and Clayey Silt (ML), sandy, olive gray, numerous angular clayey siltstone fragments, abundant roots and rootlets to½", soft, slightly moist to moist. Fill: Sandy Clay (CL), mottled brown and medium to dark olive gray, fine sandy, firm to stiff, very moist. Bottom of Test Pit= 2 feet No Groundwater or Seepage TEST PIT TP-2 Soil Description Page 14 Job No. 200506 November 18, 2020 Lab Results Moisture Content = 17.6% Moisture Content =25.3% Lab Results 0-1¼ Landslide Deposit (Fill): Clayey Silt (ML), sandy, mottled dark brown and dark Moisture 1¼ - 1½ olive gray, numerous angular clayey siltstone fragments, numerous roots and rootlets to 1/8", few brick fragments, soft, slightly moist to moist. Fill: Clayey Silt to Silty Clay (MUCL), fine sandy, mottled brown and medium to dark olive gray, firm to stiff, moist to very moist. Bottom of Test Pit= 1½ feet No Groundwater or Seepage Martin R. Owen PE, GE Geotechnical Engineer Content = 15.8% Moisture Content = 18.4% Response to Third-Party Geotechnical Review and Supplemental Geotecbnical Page 15 Investigation of Slope Failure 2210 Plaza Bonita Job No. 200506 Carlsbad, CA 92009 November 18, 2020 Depth Feet 0-½ Depth Feet 0-½ FIGURE 3 TEST PIT LOGS (Continued) by Stephen E. Jacobs, CEG TEST PIT TP-3 Soil Description Fill: Clayey Silt to Silty Clay (MUCL), fine sandy, mottled brown and medium to dark olive gray, some roots and rootlets to 1/8", numerous angular dark olive gray clayey siltstone fragments, soft to firm, moist to very moist. @ ¼', firm to stiff, very moist. Bottom of Test Pit = ½ foot No Groundwater or Seepage TEST PIT TP-4 Soil Description Fill: Clayey Silt to Silty Clay (MUCL), fine sandy, mottled brown and medium to dark olive gray, some roots and rootlets to 1/8", numerous angular dark olive gray clayey siltstone fragments, soft to firm, moist to very moist. @¼',firm to stiff, very moist. Bottom of Test Pit=½ foot No Groundwater or Seepage Notes: Test pits were hand excavated, logged, and backfilled on November 12, 2020. All measurements were taken from existing grade at top of test pit. M artin R. Owen PE, GE Geotechntcal Engineer Lab Results Lab Results Response to Third-Party Geotechnical Review and Supplemental Geotechnical Investigation of Slope Failure 2210 Plaza Bonita Carlsbad, CA 92009 130 120 1i 110 l lo "' j Ill i aJ 100 90 FIGURE 4 CROSS SECTION A-A' SCHEMATIC ONLY, NOT FOR CONSTRUCTION A A' -N 85"E Al1>ll of Pmposad t, l . Es1im31od Pro-J ~T 120 Qaf 110 Pt.Sid• --Topography -amProposad -• :~:-~~sa '"'1ishod a~. ~--·/ _Jr--.,.- •' _.rr- 100 . •·· , __ .... --' 1_, : .fl,,'"•--· - Tsa (5• Vo'WN, FfqOC1od ID 90 •---Tan and Kannedy, 1996) 80 ..... ----------------------80 0 10 """' _ _,.., Feet ote,: Al. locations are appcoxlmaie. ne current topography based on site obse,vabcns: pre-5.lae and pee- ass grading topog(ajlhy from excerpt or grading p&ans tor La Costa Valey Unit No. 4, County 01 San ~-<Sa.led I 96& and County ot San Diego opographic Survey. Sheet No. 358-1689, dated t960 and 1976; addlllcnal otm surtace elevations taken from Google Eanh {2020} Imagery. Ota ,. Landslide Deposit (Lates1 Holocene, Oaf :: Artl11dal Flll (Late Holocene) Taa = sanuago Formation (Eocene) •• -?-Approximate geologic contact querIeo wnere coniectured • Approximate ItmI1s ot proposecJ remeCllaJ gradrig Geotechnical Engineer 1i l •• ., j Ill i ID Page 16 Job No. 200506 November 18, 2020 Response to Third-Party Geotechnical Review and Supplemental Geotechnical Investigation of Slope Failure 2210 Plaza Bonita Carlsbad, CA 92009 FIGURE 5 CROSS SECTION B-B' SCHEMATIC ONLY, NOT FOR CONSTRUCTION B -N 85'E B' Anl• of o,;od 130 130 Poalllodl 120 120 'Iii 110 :. Pro•Slid1t Tc11ograi,hy ,. Qaf 110 ...... •• Ill .§ l m 100 90 anc!Prop,,.ad ~-" F'"•iidu:d Grade _#·-. •,. - ; .ir-11' ·-.. ~--······ -• ~~----.. ,. JI" ...• •••• --.It'-;-...... .... Tsa r-----. ~.:-••• ' \ TNo 0., cii Boddi,g (5 • Wt..W, pn,j,octcd lo scc6on 1rom T~r> and l<onnedf. 1 !191) 100 90 80 ..... -----------------------80 0 10 ,......_ __,.., Feet ates: Al locations are aciproxlrnate. site curra>t topography based on sit& observaUon!I: pre-slide and pc~ as,~ gradllg topograpny trom excerpt or grading plalw tor La Costa V~ Unit No. 4. County o1 San Otego. Claled 1!169 end County 01 San Oiego opographlc Survey, Sheet No. 358-1689. dated 1960 ancJ 1976; additional ounCf wr1aoe elevations taken 1rom Google Earth \2020} lmage,y. E.l!PIAOilJQQ: 01• = Landslide Deposit (Lato.st Holocene) 0.af = Armlclal Flll (Late Holocene) Taa = sanuago Formation (Eocene) •• °'!• Approximate geologic comact. Ql.letle<l wnere coniectureo Approximate limits 01 proposed remedial graatlg Geotechnical Engineer Page 17 Job No. 200506 November 18, 2020 lii l ., .. s "' ~ m Response to Third-Party Geotechnical Review and Supplemental Geotechnical Investigation of Slope Failure Page 18 Job No. 200506 November 18, 2020 2210 Plaza Bonita Carlsbad, CA 92009 N 1 FIGURE 6 REGIONAL GEOLOGIC MAP LE.GENO.: GeolOgle contact 5 Strike and ~ of Bedding 0.1 Alluvium ami COlluvtum (HolOcene) Qls t.aruJSllde oeposltS (Holocene and Plelstocer.e) TH santtago Formauon (Eocene) KJsp Undltterentlated sannago Peal< voIcan1es (Jurassic 10 Cretaeeous} BASE MAP: Modified excerpt of Geologic Maps of the Northwestern Part of San Diego County, California. Plate 2, Geologic Map of the Encinitas and Rancho Santa Fe 7.5'0uadrangles, by Tan and Kennedy (1996). ~' •• , ,-~--- 0 . -24 ~~--:. r _, .,-H• l • ... -- ✓ ...... ':\,•, 11,'t •: ··' ' • • l . •. J ~ f ,.. ,,,. • :.s ,k.)..j~ ,' . . -. A'. ' :f • . ,:,._/.I:' ,.._.. _, •• f(":_...,,, I • ., ~:: ,A~,--J· ,:n. , l ~. ~ .. ~-... ; ~ .... ... ._, " ,~ ... . --(' . _: ,~ ,·-: , ' _-4,-,p.£:......~y ~---........ -_..~~___;....; ~ ....... ~~~ ½ 1 MILES m.an1n K. uwen rl!i, Ul!i Geotechntcal Engtnnr Response to Third-Party Geotechnical Review and Supplemental Geotechnical Page 19 Investigation of Slope Failure 2210 Plaza Bonita Job No. 200506 Carlsbad, CA 92009 November 18, 2020 2210 Plaza Bonita FIGURE 7 SLOPE REPAIR SCHEMATIC ONLY EAST-WEST SECTION THROUGH SLOPE ~5• ~ I ' ' ~Scarp Restored Slope 1.5:1 (H:V) ' ' / Approx. ' ' ' ' Geogrid Layers at Height Intervals ;J 4'Max. 2' High Approx/ Fill Benches ~ 2' Deep Min.~ Fill Key Martin R. Owen PE, GE Geotechnical E ngineer ,~ -..- I I\ 15' Approx. Lower Level \ 'I 5' ➔I Min.