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HomeMy WebLinkAboutCDP 2021-0024; BLAUVELT RESIDENCE; GEOTECHNICAL INVESTIGATION FOR PROPOSED PREVIOUS TWO-STORY SINGLE FAMILY RESIDENCE; 2021-02-24Paul Blauvelt 1060 Northwood Drive EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. 10925 HARTLEY ROAD, SUITE "I" SANTEE, CALIFORNIA 92071 TEL. 619-258-7901 San Carlos, California 94070 February 24, 2021 Project No. 21-1106E6 Subject: Geotechnical Investigation for Proposed Two-Story, Single-Family Residence 3259 Lincoln Street Carlsbad, California 92008 Dear Mr. Blauvelt: In accordance with your request, we have performed a geotechnical investigation at the subject site to determine the geotechnical site conditions and provide recommendations for design and construction of the proposed single-family residence. 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 three test borings within the general area of the proposed single-family residence. 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 Two-Story, Single-Family Residence 3259 Lincoln Street Carlsbad, CA 92008 SITE DESCRIPTION AND PROPOSED CONSTRUCTION Page2 February 24, 2021 Project No. 21-1106E6 The site location is shown on the attached Vicinity Map, Figure 1. The site consists of a rectangular-shaped, residential lot located on the west side of Lincoln Street, in Carlsbad, California (see Figure 2). The lot is bordered by Lincoln Street to the east, an apartment complex to the north and other homes to the west and south. The site is presently occupied by existing residential buildings, which will be demolished. The lot slopes gently down to the east. Site vegetation consists of grass, shrubs and a few trees. The proposed construction consists of a two-story, wood framed, single-family residence. The residence will be supported on continuous and/or individual spread footings and will have a slab- on-grade floor. SUBSURFACE EXPLORATION AND LABORATORY TESTING The subsurface exploration consisted of drilling three test borings on February 3, 2021 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 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 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 the test borings presented on Figure 3. The following is a generalized description of the soils. Topsoil: Topsoil was encountered in the test borings to depths of 1.5 to 2 feet. The topsoil consisted of dark brown, moist, loose and porous, silty sand with some small roots. Slopewash: Slopewash was encountered below the topsoil to depths of 2.5 to 3 feet. The slopewash consisted of reddish brown, 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 light reddish brown, moist, medium dense to dense, silty sand. EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Geotechnical Investigation for Proposed Two-Story, Single-Family Residence 3259 Lincoln Street Carlsbad, CA 92008 GROUNDWATER No groundwater was encountered in the test borings. SOIL PROPERTIES a. Compressible Soils Page 3 February 24, 2021 Project No. 21-1106E6 Our field observations and testing indicate the topsoil and slopewash encountered to a depth of about 3 feet are loose and compressible. b. Expansive Soils An expansion index test was performed on a representative sample of the slopewash. 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 building is 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 two-story residence 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 Two-Story, Single-Family Residence 3259 Lincoln Street Carlsbad, CA 92008 b. Temporary Slopes and Excavations Page 4 February 24, 2021 Project No. 21-1106E6 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). Recommendations for shoring design can be provided by our office if desired. c. Soil Removals Within the area of the proposed construction and to a distance of at least 5 feet outside building limits, the loose topsoil and slopewash should be removed down to medium dense to dense terrace deposits, an estimated depth of about 3 feet, and replaced with fill soils compacted to at least 90 percent relative compaction. Actual removal depths should be confirmed during grading by our field representative. 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 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. 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 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 EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Geotechnical Investigation for Proposed Two-Story, Single-Family Residence 3259 Lincoln Street Carlsbad, CA 92008 Page 5 February 24, 2021 Project No. 21-1106E6 measures have been installed. After completion of grading, all excavated surfaces should exhibit positive drainage and eliminate areas where water might pond. FOUNDATIONS AND FLOOR SLABS • 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. • 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 bearing in properly compacted fill soils. 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 in properly compacted fill may be resisted by an equivalent fluid passive soil pressure of 300 pounds per cubic foot. A coefficient of friction of 0.35 may also be used. If passive and friction values are used together, the passive value should be reduced by one-third. • All footing excavations should be inspected and approved by our field representative. Footing excavations should be thoroughly cleaned prior to inspection. • Floor slabs, including garage 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. SURFACE DRAINAGE 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. Roof gutters and downspouts connecting to solid, outlet pipes are recommended. Outlet pipes should be discharged to an approved outlet. EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Geotechnical Investigation for Proposed Two-Story, Single-Family Residence 3259 Lincoln Street Carlsbad, CA 92008 LIMITATIONS OF INVESTIGATION Page 6 February 24, 2021 Project No. 21-1106E6 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. 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, which are provided by our firm, and should be budgeted within the cost of development. EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Geotechnical Investigation for Proposed Two-Story, Single-Family Residence 3259 Lincoln Street Carlsbad, CA 92008 Page 7 February 24, 2021 Project No. 21-1106E6 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. Geotechnical Investigation for Proposed Two-Story, Single-Family Residence 3259 Lincoln Street Carlsbad, CA 92008 FIGURE 1 VICINITY MAP Carfsbad State Beach VILLAGE -u-Std:~ f.l DOWNTOWN CARLSBAD 9 32S9 Lincoln St, Carlsbad, CA 92008 "·g -.1cc·-. Seafo~ & S~e?i<:'"~. ii BARRIO NORTH BEACH Page 8 February 24, 2021 Project No. 21-1106E6 EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Geotechnical Investigation for Proposed Two-Story, Single-Family Residence 3259 Lincoln Street Carlsbad, CA 92008 FIGURE2 LOCATIONS OF TEST BORINGS LEGEND B-3 APPROXIMATE LOCATION OF TEST BORING Page 9 February 24, 2021 Project No. 21-1106E6 EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Geotechnical Investigation for Proposed Two-Story, Single-Family Residence 3259 Lincoln Street Carlsbad, CA 92008 DEPTH Surface 1.5' 2.5' 6.0' DEPTH Surface 2.0' 3.0' 4.0' DEPTH Surface 2.0' 3.0' 5.0' FIGUREJ LOGS OF TEST BORINGS TEST BORING B-1 SOIL DESCRJPTION TOPSOIL dark brown, moist, loose, porous, silty sand with rootlets SLOPEWASH reddish brown, moist, loose to medium dense, silty sand TERRACE DEPOSITS light reddish brown, moist, medium dense to dense, silty sand bottom oftest boring, no caving, no groW1dwater test boring drilled and backfilled 2/3/2021 TEST BORING B-2 SOIL DESCRJPTION TOPSOIL dark brown, moist, loose, porous, silty sand with rootlets SLOPEWASH reddish brown, moist, loose to medium dense, silty sand TERRACE DEPOSITS light reddish brown, moist, medium dense to dense, silty sand bottom of test boring, no caving, no groundwater test boring drilled and backfilled 2/3/2021 TEST BORING B-3 SOIL DESCRJPTION TOPSOIL dark brown, moist, loose, porous, silty sand with rootlets SLOPEWASH reddish brown, moist, loose to medium dense, silty sand TERRACE DEPOSITS light reddish brown, moist, medium dense to dense, silty sand bottom of test boring, no caving, no groundwater test boring drilled and backfilled 2/3/2021 Y = DRY DENSITY IN PCF M = MOISTURE CONTENT IN % Page 10 February 24, 2021 Project No. 21-1106E6 y M 114.3 11.0 y M y M 100.2 10 .8 EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Geotechnical Investigation for Proposed Two-Story, Single-Family Residence 3259 Lincoln Street Carlsbad, CA 92008 FIGURE4 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' 9.4 19.1 110.6 0 Page 11 February 24, 2021 Project No. 21-1106E6 EXPANSION POTENTIAL NON- EXPANSIVE EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Geotechnical Investigation for Proposed Two-Story, Single-Family Residence 3259 Lincoln Street Page 12 February 24, 2021 Project No. 21-1106E6 Carlsbad, CA 92008 FIGURE 5 SEISMIC DESIGN VALUES 3259 Lincoln St, Carlsbad, CA 92008, USA Date Design Code Reference Document Risk Category Site Class Type Value s, 1.094 51 0.395 s~,s 1.162 S'-": null -See Section 11.4 8 S:,s 0.775 S:: null -See Section 11.4.8 Type Value SDC null -See Section 11.4.8 F. 1.062 Fv null -See Section 11.4.8 Description Description 2/23/2021, 8:25:02 AM ASCE7-16 D -Stiff Soil C& ground mo ion. ( or 0.2 second period) MCE~ 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 umeric seismic design ,alue at 1.0 second SA Seismic design category Stte amprtication factor at 0.2 second Site amplification factor at 1.0 second EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC.