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HomeMy WebLinkAboutNCP 2022-0004; AYOUB ADDITION AND ADU; GEOTECHNICAL INVESTIGATION STUDY; 2021-11-30David & Felisha Ayoub 5065 Los Robles Drive Carlsbad_ California 92008 EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. 10925 HARTLEY ROAD, SUITE "I" SANTEE, CALIFORNIA 92071 TEL. 619-258-7901 /1UG c 1 2022 No\'ernber 30. 2021 Project No. 21-112602 Subject: Geotechnical Investigation for Proposed One-Story Residence Addition and Attached ADU 5065 Los Robles Drive Carlsbad, California 92008 Dear Mr. & Mrs. Ayoub: In accordance with your request. we have perfiJrmed a geotechnical investigation at the subject site to evaluate the geotechnical site conditions and provide recommendations for design and construction of the proposed one-story residence addition and attached ADU. SCOPE OF SERVICES The following scope of work was perfom1ed for this investigation: 0 Site reconnaissance and review of published gcologil'. and gcotcchnical reports and maps pertinent to the project area. 0 Subsurfa<.:e exploration consisting of drilling three test borings within the general area of the proposed construction. The test borings were logged by our project supervisor. 0 Collection of representative soil samples at selected depths. The obtained samples were stored in scaled containers and transported to the soil testing laboratory for subsequent analysis. 0 Laboratory testing of samples representative of the types of soils encountered during the subsurface exploration. 0 Geotechnical analysis of the field and laboratory data, which provided the basis for our conclusions and recommendations 0 Production of this repm1. which summarizes the results of the above analysis and presents our findings and recommendations for the proposed construction. • Geotechnical Inwstigation for Proposed Onc-Stot1· Residence Addition and Attached ADU 5065 Los Robles Drh·e Carlsbad, California 92008 SITE DESCRIPTION AND PROPOSED CONSTRUCTION Page 2 Nowmher 30, 2021 Project No. 21-1126G2 The site location is shown on the attached Vicinity Map, Figure 1 The site is a rectangular-shaped, residential lot located on the west side of Los Robles Drive in Carlsbad, California. The lot is bordered by Los Robles Drive to the east and other residences to the west, south and north. The site is presently occupied by a one-story, single-family residence. The lot slopes slightly down to the east. Vegetation consists of grass, shrubs and trees. The preliminary plans prepared by Wright Design, of Carlsbad, California indicate that the proposed construction will consist of a one-story, wood framed, residence addition with a roof deck and an attached ADU The additions will be founded on continuous and/or individual spread footings with raised-wood and/ or slab-on-grade floors. SUBSURFACE EXPLORATION AND LABORATORY TESTING Three test borings were drilled on October 13, 202 I to a maximum depth of 6 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 to evaluate the pertinent engineering properties of the foundation soils. The laboratory tests included in-place moisture content and dry density tests and an expansion index test. The tests were performed in accordance with ASTM standards. The test results are shown on the Logs of Test Borings, Figure 3 and on the Results of Laboratory Tests, Figure 4. SUBSURFACE SOIL CONDITIONS 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 Test Borings, Figure 3, and are summarized, as follows: Topsoil: Topsoil was encountered in the test borings to a depth of 12 to 18 inches and consisted of dark brown, dry to moist, loose and porous, silty sand with some small roots. Slopewash: Slopewash was encountered beneath the topsoil to a depth of 2 to 2.5 feet The slopewash consisted of light reddish brown, dry to moist, loose to medium dense, silty sand. Terrace Deposits: Terrace deposits were encountered beneath the slopewash to the maximum depth explored of 6 feet The terrace deposits consisted of reddish brown, dry to moist, medium dense to dense, silty sand. EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. G<-'Otechnical Investigation for Pro11oscd Onc•Ston Residence Addition and Attached ADU • 5065 Los Rol)lcs D1fre Carlsbad, California 92008 SOIL PROPERTIES a. Compressible Soils PageJ No\-·cmber 30, 2021 Project No. 21·1126G2 Our field observations and testing indicate that loose, compressible topsoil and slopewash exist to a dep~~ of about 2 to 2.5 feet below existing grades. New footings for support of the proposed one-story add1t10ns should be extended through the topsoil and slopewash into the underlying, medium dense to dense terrace deposits. b Expansive Soils An expansion index test (ASTM D 4829) was performed on a representative sample of the terrace deposits. The results of the test are shown on Figure 4 An expansion index of O was obtained which indicates the terrace deposits are non•expansive. GROUNDWATER No groundwater was not encountered in the test borings. SEISMIC DESIGN VALUES Seismic design values are presented on the attached Figure 5. CONCLUSIONS Construction of the proposed one-story addition and ADU is feasible from a geotechnical standpoint provided the recommendations presented in this report are properly implemented during construction. RECOMMENDATIONS SITE GRADING a. Site Clearing Areas of new construction should be cleared of vegetation, surface obstructions and other deleterious materials. These materials should be properly disposed of off.site. b. Removal of Loose Surface Soils Within new floor slab areas, the loose topsoil and slopewash should be removed down to medium dense to dense terrace deposits a depth of about 2 to 2.5 feet below existing grades, and replaced with fill soils compacted to at least 90 percent relative compaction. Actual removal depths should be confinned during grading by our field representative. EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Gcotechnical Investigation for Proposed One-Story Residence Addition and Attached ADU 5065 Los Robles Drh·e Carlsbad, California 92008 c. Temporary Slopes and Excavations Page4 No\'ember JO, 2021 Project No. 21-1126G2 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 I : I (horizontal to vertical). 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 and trench backfill should be compacted to a minimum relative compaction of 90 percent as detennined by ASTM D1557 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. 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 soils 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 b1fades 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. FOUNDATIONS a. The proposed one~story building additions may be supported on continuous and/or individual spread footings extending through the upper loose topsoil and slopewash and at least 6 inches into the underlying medium dense to dense terrace deposits. Total footing depths should be at 2.5 to 3 feet below adjacent, existing grades. New, 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 EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Geotechoical lol'estigatioo for Proposed One-StorJ Residence Addition and Attached ADU 5065 Los Robles Dri,·e Carlsbad, California 92008 Pa~c 5 No,·ember JO, 202 I Project No. 21-1126G2 placed on concrete blocks at the bottom of the footing. Footing depths should be confirmed by our field representative. b An ~llowable soil be.ari~g. value of 2,000 pounds per square foot may be used for the design of continuous and/or md1VJdual spread footings bearing in medium dense to dense terrace deposits. This value may be increased by one-third for short term wind or seismic loads. c. Lat~ral loads may be resisted by an equivalent fluid passive soil pressure of 350 pounds per cubic foot. A coefficient of friction of 0.4 may also be used. If passive and friction values are used together, the passive value should be reduced by one-third. d_ All footing excavations should be inspected and approved by our field representative. e. For design purposes, total and differential settlements of 1/2 inch may be utilized. FLOOR SLABS 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 of0.5 No special inspection of concrete is required. Some shrinkage cracks are still possible. DRAINAGE Surface water should not be allowed to pond next to buildings, Finished grades should slope at least 2 percent away from buildings and along drainage swales. 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. EAST COUNTY SOIL CONSULTATION AND ENGINEERJNG, INC. Geotcchnical Investigation for Proposed One-Storl Residence Addition and Attached ADU 5065 Los Robles Drh•e Carlsbad, California 92008 Page6 NOl-'ember 30, 2021 Project No. 21-1126G2 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 test borings, test pits 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 cany 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. ADDITIONAL SERVICES 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 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. Respectfully Submitted, Martin R. Owen, PE, GE Geotechnical Engineer Attachments: Figures 1 through 5 EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. ~otechnical Investigation for Proposed One-Story Residence Addition and Attached ADU 5065 Los Robles Drive Carlsbad, California 92008 FIGURE 1 VICINITY MAP Can rnn Substatron f Q 5065 Los RoblesJ)r. Car1sbad. CA 920b fwest Page 7 November 30, 2021 Project No. 21-1 126G2 F EAST COUNTY SOIL CONSUL TATJON AND ENGINEERING, INC. Geotechnical Investigation for Proposed One-Story Residence Addition and Attached ADU 5065 Los Robles Dri,1e Carlsbad, California 92008 FIGURE2 LOCATIONS OF TEST BORINGS LEGEND B-3 APPROXIMATE LOCATION OF TEST BORING Page8 November 30, 2021 Project No. 21-l126G2 EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Gcotechnical Investigation for Prof)oscd Onc-Ston· Residence Addition and Attached ADU • 5065 Los Rohles Dril'e Carlsb11d, California 92008 DEPTH Surface 1.0' 2()' 4.0' DEPTH Surface 1.5' 2.5' 5.0' DEPTH Surface 1.0' 2.0' 4 ()' FIGUREJ LOGS OF TEST BORINGS BORING B-1 SOIL DESCRJPTION TOPSOIL dark brown, dry, loose, silty sand with small roots SLOPEWASH light reddish brown, dry, loose to medium dense. siltv sand TERRACE DEPOSITS • reddish bro\\n, drv to moist, medmm dense to dense si!tv sand bottom of boring, ·no caving, no groundwater ' • Boring backfilled l 0/ 13/2021 BORING B-2 SOIL DESCRJPTIDN TOPSOIL dark brown, dry. loose, silty sand with small roots SLOPEWASH light reddish brO\\TI, dry, loose to medium dense, silty sand TERRACE DEPOSITS reddish brO\m, dry to moist, medium dense to dense, silty sand bottom of boring, no caving, no groundwater Boring backfilled I0/ 13/202 I SOIL DESCRIPTION TOPSOIL BORING B-3 dark bro,.,n, d0, loose, silty sand with small roots SLOPEWASH light reddish brown, dry. loose to medium dense, silty sand TERRACE DEPOSITS reddish brown, dry to moist, medium dense to dense, silty sand bottom of boring, no caving. no groundwater Boring backfilled 10/13/202 J Page 9 Nm·cmher 30, 2021 Project No. 21-1126G2 y M y M l 16.5 6.5 y M Ya DRY DENSITY IN PCF M a MOISTURE CONTENT IN % EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Gcotcchnical Investigation for Proposed One-Story Residence Addition and Attached ADU 5065 Los Robles Dril-'c Carlsbad, Californitt 92008 FIGl:RE 4 RES UL TS OF LABORATORY TESTS TEST INITIAL LOCATION MOISTURE CONTENT (%) B-1 ,?( 2.5' 9.3 ·-· EXPANSION INDEX /ASTM D 4829\ SATURATED INITIAL DRY EXPANSION MOISTURE DENSITY INDEX CONTENT (PCF) (%) 18.l 112.0 () ·~ ·-· Page 111 November 30, 2021 Project No. 21-1126G2 EXPANSION POTENTIAL NON- EXPANSIVE EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. GeotechnicaJ lnwstigation for Proposed One-Story Residence Addition and Attached ADU 5065 Los Robles Dril'e Carlsbad, California 921108 FIGURE 5 SEISMIC DESIGN VALUES The following CBC seismic design values may be used: ~065 los Rob!es Dr, Cadsb.id, CA 92008, USA Date Design Code Reference Document Risk Category Sit. Cius Type DeKriptlon Page J J Noi·emberJ0, 202J Project No. 2J-IJ26G2 l'J/26,i202L 9.31:25 AM II D • Stiff Soil Value 1.12 MCE~ gwund motion. (for 0.2 second pe1 ,od) S, s ... S:: Type SD( F F. 0 ,103 1.178 null •See Section 11.4.8 0.785 mill -See Section 11.4.8 Value null -See Section ~14.B 1.052 null -See Section '.:.: 4.8 Description Site-modil1ed spectral acceleration value Site n10dif1ecl ~pe(tral acr.eleration valL1e Nu,neric seismic design ·1alue at 02 second SA Numeric se1sn1ic des,gn val.,e at l O serond SA Seismic design category Site amplification factoi at ll.2 second EAST COUNTY SOIL CONSULTATIO~ AND ENGINEERING, INC.