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HomeMy WebLinkAboutPD 2022-0022; CANTOR GARAGE ADDITION; GEOTECHNICAL INVESTIGATION FOR PROPOSED GARAGE AND RETAINING WALLS; 2021-06-28Josh Cantor 4215 Hillside Drive Carlsbad, California 92008 EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. 10925 HARTLEY ROAD, SUITE "I" SANTEE, CALIFORNIA 92071 TEL. 619-258-7901 June 28, 2021 Project No. 21-1106G7 Subject: Geotechnical Investigation for Proposed Garage and Retaining Walls 4269 Hillside Drive Carlsbad, California 92008 Dear Mr. Cantor: In accordance with your request, we have performed a geotechnical investigation at the subject site to evaluate the geotechnical site conditions and provide recommendations for design and construction of the proposed garage and retaining walls. SCOPE OF SERVICES The following scope of work was performed for this investigation: 0 Site reconnaissance and review of published geologic and geotechnical reports and maps pertinent to the project area. 0 Subsurface exploration consisting of drilling two test borings within the area of the proposed garage. The test borings were logged by our project supervisor. 0 Collection of representative soil samples at selected depths. The obtained samples were stored in moisture-resistant containers and transported to our soil testing laboratory for subsequent analysis. 0 Laboratory testing of soil samples obtained during the subsurface exploration. 0 Geotechnical analysis of the field and laboratory data, which provided the basis for our conclusions and recommendations. 0 Preparation of this report, which summarizes the results of our analysis and presents our findings and recommendations for the proposed construction. Geotechnical Investigation for Proposed Garage and Retaining Walls 4269 Hillside Drive Carlsbad, CA 92008 SITE DESCRIPTION AND PROPOSED CONSTRUCTION Page2 June 28 2021 Project No. 21-1106G7 The site location is shown on the attached Vicinity Map, Figure 1. The site consists of an irregular- shaped residential lot in Carlsbad, California (see Figure 2). The lot is bordered by Hillside Drive to the northeast and residential parcels to the north, west and south. The proposed garage is located in a mostly cut portion of the lot. The lot slopes generally down to the east. Site vegetation is relatively minor. The proposed garage will be a one-story, wood framed structure supported on continuous and/or individual spread footings with a slab-on-grade floor. Retaining walls will be constructed along the west and north sides of the proposed garage. SUBSURFACE EXPLORATION AND LABORATORY TESTING Two test borings were drilled on April 21 , 2021 to a maximum depth of 7 feet with a hand auger. The approximate locations of the test borings are shown on Figure 2. Logs of the test borings are shown on Figure 3. Following the subsurface exploration, laboratory testing was performed on representative soil samples to evaluate the pertinent engineering properties of the foundation materials. The laboratory tests included moisture content, dry density and expansion index tests. The tests were performed in accordance with ASTM standards. The test results are shown on the Logs of the Test Borings, Figure 3 and on Figure 4, Results of Laboratory Tests. SUBSURFACE SOIL CONDIDONS The subsurface soil descriptions were interpreted from conditions encountered during the subsurface exploration and/or inferred from the geologic literature. Detailed descriptions of the subsurface soils are presented on the logs of the test borings presented on Figure 3. The following is a generalized description of the soils. Fill: Fill soils were encountered in Boring B-2 to a depth of approximately 0.5 foot. The fill consisted of dark grayish brown, dry, loose, silty sand. Natural Soil: Natural soil was encountered below the fill in Boring B-2 and below the ground surface in Boring B-1 to the maximum depth explored of 7 feet. The natural soil consisted of dark to reddish brown, moist, loose to medium dense, silty sand to a depth of 2 feet, underlain by moist, medium dense, silty sand to the depth explored of 7 feet. GROUNDWATER No groundwater was encountered in the test borings. EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. GeotechnicaJ Investigation for Proposed Garage and Retaining WaJls 4269 Hillside Drive Carlsbad, CA 92008 SOIL PROPERTIES a. Compressible Soils Page 3 June 28 2021 Project No. 21-1106G7 Our field observations and testing indicate the upper fill and natural soil are loose and compressible to a depth of about 2 feet. b. Expansive Soils An expansion index test was performed on a representative sample of the natural soil. The results of the test are shown on Figure 4. An expansion index of O was obtained, which indicates the soils are non-expansive. GEOLOGY From published geologic maps, the site is underlain at depth by sedimentary terrace deposits. There are no known geologic hazards such as landslides, liquefaction-prone areas, or earthquake faults at the site. However, the proposed buildings are subject to ground shaking and possible damage from earthquakes on nearby, or more distant, active faults. SEISMIC DESIGN VALUES Seismic design values are presented on Figure 5. CONCLUSIONS Construction of the proposed one-story garage and retaining walls is feasible from a geotechnical standpoint, provided the recommendations presented in this report are properly implemented during construction. RECOMMENDATIONS SITE GRADING a. Site Clearing The area of the proposed construction should be cleared of vegetation, surface obstructions and other deleterious materials. Vegetation and debris from the clearing operation should be properly disposed of off-site. EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Geotechnical Investigation for Proposed Garage and Retaining Walls 4269 Hillside Drive Carlsbad, CA 92008 b. Temporary Slopes and Excavations Page4 June 28 2021 Project No. 21-1106G7 Temporary, vertical slopes and excavations should not exceed 5 feet in height. Temporary slopes and excavations greater than 5 feet in height should be shored or laid back at a maximum inclination of 1 : 1 (horizontal to vertical). Recommendations for shoring design can be provided by our office if desired. c. Soil Removals Within the area of the proposed garage and retaining walls and to a distance of at least 5 feet outside building limits, the loose fill and natural soils should be removed down to medium dense natural soil, an estimated depth of about 2 feet, and replaced with fill soils compacted to at least 90 percent relative compaction. d. Compaction and Method of Filling Prior to fill placement, the exposed subgrade soils should be scarified to a depth of 6 to 8 inches, moisture conditioned to slightly above optimum moisture content and compacted to at least 90 percent relative compaction. The on-site soils may be reused as compacted fill, provided they are free of organic materials and debris, and rocks or cobbles over 6 inches in dimension. Any imported fill soils should be predominantly granular and approved by our field representative. All fill should be compacted to a minimum relative compaction of 90 percent as determined by ASTM Dl557. Fill should be placed at a moisture content slightly above optimum moisture content, in lifts 6 to 8 inches thick, with each lift compacted by mechanical means. Utility trench backfill and retaining wall backfill should also be compacted to at least 90 percent relative compaction. All grading, fill placement, and compaction should be performed in accordance with the grading requirements of the City of Carlsbad. Fill placement and compaction should be observed and tested as necessary by our field representative. EROSION CONTROL Due to the predominantly sandy nature of the on-site soils, areas of recent grading or exposed ground may be subject to erosion. During construction, surface water should be controlled via berms, gravel/ sandbags, silt fences, straw wattles, siltation or bioretention basins, positive surface grades or other method to avoid damage to the finish work or adjoining properties. All site entrances and exits must have coarse gravel or steel shaker plates to minimize offsite sediment tracking. Best Management Practices (BMPs) must be used to protect storm drains and minimize pollution. The contractor should take measures to prevent erosion of graded areas until such time as permanent drainage and erosion control measures have been installed. After completion of grading, all excavated surfaces should exhibit positive drainage and eliminate areas where water might pond. EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Geotecbnical Investigation for Proposed Garage and Retaining Walls 4269 Hillside Drive Carlsbad, CA 92008 FOUNDATIONS AND FLOOR SLABS Pages June 28 2021 Project No. 21-1106G7 • Continuous and/or individual footings should be founded in properly compacted fill at a minimum depth of 18 inches below building pad grade or lowest adjacent, finished grade, whichever is deeper. • Continuous footings should be at least 12 inches wide and reinforced with a minimum of four #4 steel bars; with two bars placed near the top of the footings and the other two bars placed near the bottom of the footings. Individual footings should be at least 18 inches square and reinforced with a grid of #4 bars spaced 12 inches on centers ( each way) and placed on concrete blocks at the bottom of the footing. Retaining wall footings should be designed by the project structural engineer. • An allowable soil bearing value of 2,000 pounds per square foot may be used for the design of continuous and/ or individual spread footings and retaining wall footings bearing in properly compacted fill or medium dense natural soil. This value may be increased by one-third for short term wind or seismic loads. • For design purposes, total and differential settlements of½ inch may be assumed. • Lateral loads may be resisted by an equivalent fluid passive soil pressure of 300 pounds per cubic foot. A coefficient of friction of 0.3 may also be used. If passive and friction values are used together, the friction value should be reduced by one-third. • All footing excavations should be inspected and approved by our field representative. Footing excavations should be properly cleaned prior to inspection. • Floor slabs should be at least 5 inches thick and reinforced with #4 bars placed at 18 inches on centers in two directions in the middle of the slab. The reinforcing steel should be supported on steel chairs or concrete blocks. Floor slabs should be underlain by 2 inches of clean sand over a 10-mil visqueen moisture barrier over 2 inches of clean sand. To minimize the potential for shrinkage cracks, concrete should have a minimum compressive strength of 3,000 psi and maximum water-cement ratio of 0.5. No special inspection of concrete is required. Some shrinkage cracks are still possible. EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Geotechnical Investigation for Proposed Garage and Retaining Walls 4269 Hillside Drive Carlsbad, CA 92008 RETAINING WALLS a. Soil Pressures Page6 June 28 2021 Project No. 21-1106G7 Cantilever retaining walls may be designed for an active equivalent fluid soil pressure of 3 5 pcf for a level backfill and 55 pcf for a 2: 1 H:V sloping backfill assuming predominantly sandy, very low expansive backfill soils (El less than 20). Should the walls be subject to a uniform surcharge load behind the walls, they should be designed for an additional, uniform lateral pressure equal to one- third the anticipated surcharge pressure. Basement and restrained retaining walls may be designed for an at-rest equivalent fluid soil pressure of 55 pcf for a level backfill and 75 pcf for a 2: 1 sloping backfill assuming predominantly sandy, very low expansive backfill soils (El less than 20). Should the walls be subject to a uniform surcharge load behind the walls, they should be designed for an additional, uniform lateral pressure equal to one-half the anticipated surcharge pressure. For cantilever or restrained retaining walls over 6 feet in height, an additional earthquake force should be applied. A horizontal seismic coefficient Kh = Sos/2.5 should be assumed . The earthquake force F = 3/8*Kh*Soil density*Wall height (H)"'2 and may be assumed to have an inverted triangular distribution with the resultant force located at a distance of 0.6*H from the base of the wall. Seismic design values are presented on the attached Figure 5. A soil density of 130 pcf may be assumed. b. Retaining Wall Foundations Retaining wall footings should be designed m accordance with the recommendations presented previously under Foundations. c. Retaining Wall Drainage and Backfill Retaining walls should be provided with appropriate waterproofing and wall drainage. Retaining wall waterproofing should be designed by the project architect or building designer. Recommended wall drainage is shown on the attached Figure 6. A 2-feet wide prism of Caltrans Class 2 Permeable Material (graded drain rock) should be placed behind the wall. Alternatively, retaining wall drainage should consist of Miradrain 6000 or J-Drain SWD-6 prefabricated drain panels placed directly against the wall. The drain panels should connect to a collector pipe at the bottom of the wall constructed in accordance with drain manufacturer's requirements. The drain pipe should flow at a 1 percent minimum gradient to an approved outlet. Retaining walls may be backfilled with imported, predominately sandy, very low expansive soils (EI less than 20) compacted to at least 90 percent relative compaction in accordance with the recommendations presented previously under Site Grading. EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Geotechnical Investigation for Proposed Garage and Retaining Walls 4269 Hillside Drive Carlsbad, CA 92008 SURFACE DRAINAGE Page 7 June 28 2021 Project No. 21-1106G7 Surface water should not be allowed to pond next to buildings. Finished grades should slope a minimum of 2 percent away from buildings and along drainage swales. Drainage gradients should be maintained . Roof gutters and downspouts connecting to solid, outlet pipes are recommended. Outlet pipes should be discharged to an approved outlet. LIMITATIONS OF INVESTIGATION Our investigation was performed using the skill and degree of care ordinarily exercised under similar circumstances by reputable soil engineers and geologists practicing in this or similar localities. No other warranty, expressed or implied, is made as to the conclusions and professional advice included in this report. This report provides no warranty, either expressed or implied, concerning future building performance. Future damage from geotechnical or other causes is a possibility. This report is prepared for the sole use of our client and may not be assigned to others without the written consent of the client and ECSC&E, Inc. The samples collected and used for testing, and the observations made, are believed representative of site conditions; however, soil and geologic conditions can vary significantly between exploration trenches, test borings and surface exposures. As in most major projects, conditions revealed by construction excavations may vary with preliminary findings. If this occurs, the changed conditions must be evaluated by a representative of ECSC&E and designs adjusted as required or alternate designs recommended. This report is issued with the understanding that it is the responsibility of the owner, or of his/her representative to ensure that the information and recommendations contained herein are brought to the attention of the project architect and engineer. Appropriate recommendations should be incorporated into the structural plans. The necessary steps should be taken to see that the contractor and subcontractors carry out such recommendations in the field . The findings of this report are valid as of this present date. However, changes in the conditions of a property can occur with the passage of time, whether they are due to natural processes or the works of man on this or adjacent properties. In addition, changes in applicable or appropriate standards may occur from legislation or the broadening of knowledge. Accordingly, the findings of this report may be invalidated wholly or partially by changes outside of our control. Therefore, this report is subject to review and should be updated after a period of two years. EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Geotecbnical Investigation for Proposed Garage and Retaining Walls 4269 Hillside Drive Carlsbad, CA 92008 ADDITIONAL SERVICES Page 8 June 28 2021 Project No. 21-1106G7 A review of plans and specifications, field observations and testing under our direction are integral parts of the recommendations made in this report. If East County Soil Consultation and Engineering, Inc. is not retained for these services, the client agrees to assume our responsibility for any potential claims that may arise during construction. Observation and testing are additional services, which are provided by our firm, and should be budgeted within the cost of development. This opportunity to be of service is appreciated. If you have any questions, or we can be of further service, please do not hesitate to call or contact us. This opportunity to be of service is appreciated . If you have any questions, or we can be of further service, please do not hesitate to call or contact us. Respectfully Submitted, Martin R. Owen, PE, GE Geotechnical Engineer Attachments: Figures 1 through 6 EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Geotechnical Investigation for Proposed Garage and Retaining Walls 4269 Hillside Drive Carlsbad, CA 92008 ~ -..cace: r ... S. s Ccr~ rs r,-. o, \! ..,..c""a""I'\ : ... rst:=c Sa rt -!-, •'3tr1d.: -, Eleme'lta,y ~ Schoo Lei.JC lid a p: = K°tcher ,,, -- V ,,.,.- l! - r "· FIGURE 1 VICINITY MAP 9 Page9 June 28 2021 Project No. 21-1106G7 ... 4269 Hillside Dr. Carlsbad. CA 92008 EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Geotechnical Investigation for Proposed Garage and Retaining Walls 4269 Hillside Drive Carlsbad, CA 92008 FIGURE2 LOCATIONS OF TEST BORINGS LEGEND Page 10 June 28 2021 Project No. 21-1106G7 B-2 • APPROXIMATE LOCATION OF TEST BORING EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Geotechnical Investigation for Proposed Garage and Retaining Walls 4269 Hillside Drive Carlsbad, CA 92008 DEPTH Surface 1.0' 2.0' 3.5' 6.0' DEPTH Surface 0.5' 2.0' 6.0' 7.0' FIGURE3 LOGS OF TEST BORINGS TEST BORING B-1 SOIL DESCRIPTION NATURAL SOIL reddish brown, moist, loose to medium dense, silty sand It ti II dark brown, moist, medium dense, silty sand reddish brown, moist, medium dense, silty sand bottom of test boring, no caving, no groundwater test boring backfilled 4/21/2021 TEST BORING B-2 SOIL DESCRIPTION FILL dark grayish brown, dry, loose, silty sand NATURAL SOIL reddish brown, moist, loose to medium dense, silty sand dark to reddish brown, moist, medium dense, silty sand reddish brown, moist, medium dense, silty sand bottom of test boring, no caving, no groundwater test boring backfilled 8/11/2020 Page 11 June 28 2021 Project No. 21-1106G7 y M 109.2 8.4 y M 118.8 9.8 ---------------------------------------------------------------------------------------------------------------------------------- Y = DRY DENSITY IN PCF M = MOISTURE CONTENT IN % EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Geotechnical Investigation for Proposed Garage and Retaining Walls 4269 Hillside Drive Carlsbad, CA 92008 FIGURE 4 RESULTS OF LABORATORY TESTS EXPANSION INDEX TEST (ASTM D 4829) TEST INITIAL SATURATED INITIAL EXPANSION LOCATION MOISTURE MOISTURE DRY INDEX CONTENT CONTENT(%) DENSITY (%) (PCF) B-1 @ 2.0' 9.3 18.2 110.8 0 Page 12 June 28 2021 Project No. 21-1106G7 EXPANSION POTENTIAL NON- EXPANSIVE EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Geotechnical Investigation for Proposed Garage and Retaining Walls 4269 Hillside Drive Page 13 June 28 2021 Project No. 21-1106G7 Carlsbad, CA 92008 FIGURES SEISMIC DESIGN V ALOES 4269 Hillside Dr, Carlsbad, CA 92008, USA Date Design Code Reference Document Risk Category Site Class Type Value Ss 1.045 51 0.379 s ... s 1.13 s-.(: null -See Section 11.4.8 Sos 0.754 5:::. null -See Section 11.4.8 Type Value soc null -See Section 11.4.8 F, 1.082 Fv null -See Section 11.4.8 Description Description 6/23/2021, 8:08:24 AM ASCE7-16 n D -Stiff Soil MCER ground motion. {for 0.2 second period) MCER ground motion. (for l.0s period) Site-modified spectral acceleration value Site-modified spectral acceleration value Numeric seismic design value at 0.2 second SA Numeric seismic design value at 1.0 second SA Seismic design category s·te amplification factor at 0.2 second Site amplification factor at 1.0 second EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Geotechnical Investigation for Proposed Garage and Retaining Walls 4269 Hillside Drive Carlsbad, CA 92008 FIGURE6 RETAINING WALL DRAINAGE CANTILEVER RETAINING WALL WATERPROOFING I 2' MIN. < >I ..... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..... . . . . . . . . . . . . . . . ..... . . . . . ..... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..... . . . . . . . . . . . . . . . . . . . . ..... . . . . . . . . . . . . . . . ..... . . . . . . . . . . . . . . . ..... . . . . . . . . . . . . . . . . . . . . 2-FEET WIDE PRISM OF CALTRANS CLASS 2PERMEABLE MATERIAL PLACED TO WlTIIlN 1 FOOT OF TOP OF WALL 4-INCH DIAMETER, PERFORATED, SCHEDULE 35 OR BETTER PVC PIPE WRAPPED IN MlRAFl FILTER SOCK. DRAIN AT 1%MIN. TO APPROVED OUTLET Page 14 June 28 2021 Project No. 21-1106G7 SPECIFICATIONS FOR CALTRANS CLASS 2 PERMEABLE MATERIAL GRADATION BY SIEVE SIZE Sieve Percentage Size Passing l" 100 3/4" 90-100 3/8" 40-100 No. 4 25-40 No. 8 18-33 No. 30 5-15 No. 50 0-7 No. 200 0-3 Class 2 Permeable Material shall also have a sand equivalent value of at least 75 . EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Josh Cantor EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. 10925 HARTLEY ROAD, SUITE "I" SANTEE, CALIFORNIA 92071 TEL. 619-258-7901 4215 Hillside Drive Carlsbad, California 92008 December 20, 2022 Project No. 21-1106G7 Subject: Reference: Response to Geotechnical Review for Proposed Garage and Retaining Walls 4269 Hillside Drive Carlsbad, California 92008 Project No. PD2022-0022, Grading Permit No. GR2022-0031 "Geotechnical Investigation for Proposed garage and Retaining Walls, 4269 Hillside Drive, Carlsbad, California 92008", Project No. 21-1106G7, Prepared by East County Soil Consultation and Engineering, Inc., Dated June 28, 2021 . Dear Mr. Cantor: In accordance with your request, we have prepared this letter in response to the subject geotechnical review for the Cantor Garage Addition, 4269 Hillside Drive, (1st Review). Comment No. 1 We have reviewed the grading plan prepared by Bha, Inc., Land Planning, Civil Engineering and Surveying for the proposed Cantor garage addition at the subject site. The grading plan was found to be in accordance with the recommendations presented in the referenced geotechnical report. Comment No. 2 Based on site geotechnical conditions and a review of the grading plan, it is our opinion that the proposed project will have no impact on adjacent off-site properties. Comment No. 3 The proposed construction will consist of a one-story, detached garage to be located east of the existing residence. In addition, a maximum 4-foot high retaining wall is planned near the bottom of the existing cut slope adjacent to the east and north property lines. The proposed grading will include an approximately 4-foot high vertical cut to accommodate the proposed retaining wall. For the proposed retaining wall and garage, we recommend the upper 2-foot of subgrade be removed to a distance of 5 feet outside perimeter footings (where feasible). The bottom of the Response to Geotechnical Review for Proposed Garage and Retaining Walls 4269 Hillside Drive Carlsbad, California 92008 Page2 December 20, 2022 Project No. 21-1106G7 excavation should be moisture-conditioned and compacted. The scarified soils along with the 2 feet of overexcavated soil should be compacted to a minimum of 90 percent relative compaction. Comment No. 4 The natural soils encountered during our site investigation revealed approximately 2 feet of loose to medium dense slopewash over medium dense terrace deposits. Comments No. 5 and 6 Please see attached Figure 1 showing a new "Locations of Test Borings" map using the most current grading plan, and a geologic cross-section. Comment No. 7 In the areas of the proposed garage and retammg wall, the subgrade soils consisted of approximately 2 feet of loose to medium dense slopewash, which we have recommended overexcavation and recompaction. The soils underlying the slopewash consisted of medium dense terrace deposits which are considered suitable for support of compacted fill soils and the proposed structure. Comment No. 8 and 9 Regional Seisrnicity Generally, Seismicity within California can be attributed to the regional tectonic movement taking place along the San Andreas Fault Zone, which includes the San Andreas Fault and most parallel and subparallel faults within the state. The portion of southern California where the subject site is located is considered seismically active. Seismic hazards are attributed to groundshaking from earthquake events along nearby or more distant Quaternary faults . The primary factors in evaluating the effect an earthquake has on a site are the magnitude of the event, the distance from the epicenter to the site and the near surface soil profile. According to the Fault-Rupture Hazard Zones Act of 1994 (revised Alquist-Priolo Special Studies Zones Act), quaternary faults have been classified as "active" faults, which show apparent surface rupture during the last 11 ,000 years (i.e., Holocene time). "Potentially-active" faults are those faults with evidence of displacing Quaternary sediments between 11,000 to 1. 6 millions years old. Seismic Analysis Based on our evaluation, the closest known "active" fault is the Rose Canyon Fault located approximately 8.5 kilometers to the west. The Rose Canyon Fault is the design fault of the project due to the predicted credible fault magnitude and ground acceleration. EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Response to Geotechnical Review for Proposed Garage and Retaining Walls 4269 Hillside Drive Carlsbad, California 92008 Page3 December 20, 2022 Project No. 21-1106G7 The Seismicity of the site was evaluated utilizing the 2008 Hazard Maps and Data from the USGS website, and Seed and Idriss methods for active Quaternary faults within the regional vicinity. The site may be subjected to a Maximum Probable Earthquake of 6.9 Magnitude along the Rose Canyon fault, with a corresponding Peak Ground Acceleration of 0.35g. The maximum Probable Earthquake is defined as the maximum earthquake that is considered likely to occur within a 100- year time period. The effective ground acceleration at the site is associated with the part of significant ground motion, which contains repetitive strong-energy shaking, and which may produce structural deformation. As such, the effective or "free field" ground acceleration is referred to as the Repeatable High Ground Acceleration (RHGA). It has been determined by Ploessel and Slosson (1974) that the RHGA is approximately equal to 65 percent of the Peak Ground Acceleration for earthquakes occurring within 20 miles of a site. Based on the above, the calculated Credible RHGA at the site is 0.23g. Geologic Hazard Assessment Ground Rupture Ground rupture due to active faulting is not considered likely due to the absence of known fault traces within the vicinity of the project; however, this possibility cannot be completely ruled out. The unlikely hazard of ground rupture should not preclude consideration of"flexible" design for on-site utility lines and connections. Liquefaction Liquefaction involves the substantial loss of shear strength in saturated soils, usually sandy soils with a loose consistency when subjected to earthquake shaking. Based on the absence of shallow groundwater and consistency of the underlying terrace deposits, it is our opinion that the potential for liquefaction is very low. Landsliding There is no indication that landslides or unstable slope conditions exist on or adjacent to the project site. There are no obvious geologic hazards related to landsliding to the proposed development or adjacent properties. Tsunamis and Seiches The site is not subject to inundation by tsunamis due to its elevation. The site is also not subject to seiches (waves in confined bodies of water). EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Response to Geotechnical Review for Proposed Garage and Retaining Walls 4269 Hillside Drive Carlsbad, California 92008 Comment No. 10 and 11 Page4 December 20, 2022 Project No. 21-1106G7 The existing cut slope adjacent to the east and north property lines appears to be weathered, unstable and steeper than required in the City of Carlsbad. A review of the grading plan indicates a retaining wall will be constructed which will stabilize the existing slope. The temporary slope should be excavated in accordance with OSHA guidelines, i.e. a maximum 5-foot high vertical cut with a maximum lH: 1 V slope above that. If property line constraints do not allow an approved temporary slope, temporary or permanent shoring may be used. Recommendations for shoring design can be provided by our office if desired. Comment No. 12 and 16 Driveways and other exterior slabs may be supported on the subgrade soils provided they are scarified to a depth of 12 inches, moisture-conditioned around the optimum moisture content and compacted to at least 90 percent relative compaction. Driveways and other exterior concrete slabs should be at least 5 inches thick and reinforced with No. 4 rebars spaced at 18 inches on centers in two directions and placed at mid-height in the slabs. Driveways and other exterior slabs should be provided with construction joints spaced no more than 10 feet apart to minimize shrinkage cracking. Slab concrete should have a minimum compressive strength of 3,000 psi and maximum water-cement ratio of 0.5 to minimize shrinkage cracking. No special testing of concrete is necessary. Some shrinkage cracking is still possible. Comments No. 13 and 14 Based on the attached sieve analysis results (Figure 2) and the expansion index test results provided in the referenced geotechnical report, a soil classification of silty sand (SM) was obtained which substantiates the soil bearing capacity, passive pressure, coefficient of friction and active pressure (3 5 pct) provided in the referenced geotechnical report and in accordance with Tables 1806.2 and 1610.1 of the 2019 California Building Code. Comment No. 15 Corrosivity tests were performed on a representative sample of the onsite soils. The attached test results (Figure 3) indicate a low degree of corrosivity. Accordingly, we recommend Type I/II Portland Cement for foundation construction. Comment No. 17 Please see attached a list of references. EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Res nse to Geotecbnical Review for Proposed Garage and Retaining Walls 4269 Hillside Drive Carl bad, California 92008 Co,imcnt N?. 18 I Pages December 20, 2022 Project No. 21-l106G7 The project ~eotechnical engineer or engineer's representative should receive advance notice to pro ide the necessary intermittent field observations and compaction testing during site dev lopment-: including overexcavation and recompaction of the building pad and during the bac ill of t~e retaining wall. In addition. we should observe that the footings have been exc vated to the proper depth and width into competent compacted fill soils prior to the pla ment of steel. Thi~ opportl$ity to be of service is appreciated. If you have any questions, or we can be of furtper service. please do not hesitate to call or contact us. Retectfully Submitte~ Ma RC 54071. GE 2704 Attjichments: Figures 1 thru 3 and References EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Response to Geotechnical Review for Proposed Garage and Retaining Walls 4269 Hillside Drive Carlsbad, California 92008 FIGURE 1 Page 6 December 20, 2022 Project No. 21-1106G7 LOCATION OF TEST BORINGS/ GEOLOGIC CROSS-SECTION .l>-Z. JZ:5r/3ClfN6(Pl';(v~ q>SVtl ~ 5~/ISH ~t EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. \ \ Response to Geotechnical Review for Proposed Garage and Retaining Walls 4269 Hillside Drive Carlsbad, California 92008 U.S. Standard Sieve Size 2" l" 1/2" 3/8" #4 #8 #16 #30 #50 #100 #200 uses FIGURE2 PARTICLE SIZE ANALYSIS (ASTMD422) Percent Passing B-2@2.0' Slopewash - - - - - 100 99 91 47 25 18 SM Page 7 December 20, 2022 Project No. 21-1106G7 Percent Passing B-1 @1.5' Terr ace Deposits - - - - - 100 99 85 38 18 13 SM EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Response to Geotechnical Review for Proposed Garage and Retaining Walls 4269 Hillside Drive Carlsbad, California 92008 FIGURE3 CORROSIVITY TEST RESULTS L A B O R A T O R Y REPORT Page8 December 20, 2022 Project No. 21-1106G7 Telephone (619) 425-1993 Fax 425-7917 Established 1928 CLARKSON LABORATORY AND SUPPL. Y INC. 350 Trousdale Dr. Chula Vista , Ca. 91910 www.clarksonlab.com A N A L Y T I C A L A N D C O N S U L T I N G C H E M I S T S Date : October 18, 2022 Purchase Order Number: NONE Sales Order Number : 57331 Account Number: EASCS To: *-------------------------------------------------* East County Soil Consultation and Engineering Inc. 10925 Hartley Road Suite I Santee, Ca 92071 Attention: Michael Duncan Laboratory Number: SO9173 Customers Phone : 258-7901 Fax: 258-7902 Sample Designation: *-------------------------------------------------* One soil sample received on 10/11/22 at 12 :30pm, marked as Highland -Cantor. Analysis By California Test 643, 1999 , Department of Transportation Division of Construction, Method for Estimating the Service Life of Steel Culverts. pH 6.5 Water Added (ml) 26 34 47 60 73 10 5 5 5 5 5 5 5 years years years years years to perforation to perforation to perforation to perforation to perforation for a 16 gauge for a 14 gauge for a 12 gauge for a 10 gauge for a 8 gauge Water Soluble Sulfate Calif. Test 417 Water Soluble Chloride Calif. Test 422 ~ RMB/js metal metal metal metal metal Resistivity (ohm-cm) 8200 culvert. culvert. culvert. culvert. culvert. 7800 6200 4800 4500 4500 4600 4800 0.004% 0.002% EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Response to Geotechnical Review for Proposed Garage and Retaining Walls 4269 Hillside Drive Carlsbad, California 92008 REFERENCES Page9 December 20, 2022 Project No. 21-1106G7 1. ''2019 California Building Code, California Code of Regulations, Title 24, Part 2, Volume 2 of 2", Published by International Code Council. 2. "Geologic Map of the San Diego 30' x 60' Quadrangle, California", by Michael P. Kennedy and Siang S. Tan, 2008. 3. "Geotechnical and Foundation Engineering: Design and Construction", by Robert W. Day, 1999. 4. "Maps of Known Active Fault Near-Source Zones in California and Adjacent Portions of Nevada to be used with 1997 Uniform Building Code", Published by International Conference of Building Officials. 5. "Geologic Maps of the Northwestern Part of San Diego County, California", Department of Conservation, Division of Mines and Geology, by Siang S. Tan and Michael P . Kennedy, 1996. 6. "Bearing Capacity of Soils, Technical Engineering and Design Guides as Adapted from the US Army Corps of Engineers, No. 7", Published by ASCE Press, 1994. 7. "Foundations and Earth Structures, Design Manual 7.2", by Department of Navy Naval Facilities Engineering Command, May 1982, Revalidated by Change 1 September 1986. 8. "Ground Motions and Soil Liquefaction during Earthquakes", by H.B. Seed and I.M. Idriss, 1982. EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Josh Cantor EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. 10925 HARTLEY ROAD, SUITE "I" SANTEE, CALIFORNIA 92071 TEL. 619-258-7901 4215 Hillside Drive Carlsbad, California 92008 March 30, 2023 Project No. 21-1106G7 Subject: 2nd Response to Geotechnical Review for Proposed Garage and Retaining Walls 4269 Hillside Drive Carlsbad, California 92008 Project No. PD2022-0022, Grading Permit No. GR2022-0031 References: 1. "Response to Geotechnical Review for Proposed Garage and Retaining Walls, 4269 Hillside Drive, Carlsbad, California 92008", Project No. 21-1106G7, Prepared by East County Soil Consultation and Engineering, Inc., Dated December 20, 2022. 2. "Geotechnical Investigation for Proposed garage and Retaining Walls, 4269 Hillside Drive, Carlsbad, California 92008", Project No. 21-1106G7, Prepared by East County Soil Consultation and Engineering, Inc., Dated June 28, 2021 . Dear Mr. Cantor: In accordance with your request, we have prepared this second response letter to the geotechnical review for the proposed garage addition on 4269 Hillside Drive, in Carlsbad, California. Comments No. 1 and 2 The attached shear test results substantiate the values used for soil bearing capacity, passive pressure, coefficient of friction and active pressure provided in the referenced geotechnical report (Reference No. 2), including an active equivalent fluid pressure of 35 pcf for the design and construction of the proposed retaining walls. Comment No. 3 In addition to the necessary intermittent field observations and compaction testing recommended in the referenced response report (Reference No. 1), requfred during site development, the geotechnical engineer or engineer's representative should observe the excavations of temporary slopes during grading and retaining wall construction, so additional recommendations may be provided, if required. Response to Geotechnical Review for Proposed Garage and Retaining Walls 4269 Hillside Drive Carlsbad, California 92008 Page2 March 30, 2023 ProjedNo. 21-1106G7 This opportunity to be of service is appreciated. If you have any questions, or we can be of further service, please do not hesitate to call or contact us. Respectfully Submitted, Mamadou Saliou Diallo, P.E. RCE 54071, GE 2704 EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Response to Geotechnical Review for Proposed Garage and Retaining Walls 4269 Hillside Drive Carlsbad, California 92008 6000 sooo "'2000 5. 1000 0 C 7000 5,000 2000 1000 0 0 1000 Norm.I .......,......._ 5tre.ss (;>sf! ........ .;.r'! -312' -4. e •• e ••• e e e e e • • -i091 " fi Shur Strain f J 2000 3000 4000 ~or.mi 5ne.s tpsf' 10 5000 6000 7000 ~ SAMPLE ID. C tor H1lslde Dnve -Carlsbad 4> 34. 11 C 659~f Brown Silty S.lnd Initial NOTES Renolded Sz~I lOfi!.. pd 11 II~..._ S1i'nplEW115 i1nd dni.Md -4,S,. East County Soils A-.-I A f:!! ----,-, I .. ,,..., --ORB 0.Jte. ""5e Fpe· Page 3 March 30, 3023 Project No. 21-1106G7 34• 524 psf Flllal 100 pcf 177 _., ..... M.lroh.2023 EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC.