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HomeMy WebLinkAboutPD 2021-0021; 3460 ROOSEVELT STREET; GEOTECHNICAL INVESTIGATION FOR PROPOSED TWO-STORY, SINGLE-FAMILY RESIDENCE; 2020-10-103460 Roosevelt, LLC cl o Craig Correll 4245 Sunnyhill Drive Carlsbad, California 92008 EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. 10925 HARTLEY ROAD, SUITE "I" SANTEE, CALIFORNIA 92071 TEL. 619-258-7901 October 10, 2020 Project No. 20-1106E6 Subject: Geotechnical Investigation for Proposed Two-Story, Single-Family Residence 3460 Roosevelt Street Carlsbad, California 92008 Dear Mr. Correll: 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 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 limits of the proposed building area. The test borings were logged by our project supervisor. 0 Collection of representative soil samples at selected depths. The obtained samples were placed in sealed 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 field investigation. 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 the above analysis and presents our findings and recommendations for the proposed construction. Geotechnical Investigation for Proposed Two-Story, Single-Family Residence 3460 Roosevelt Street Carlsbad, California 92008 SITE DESCRIPTION AND PROPOSED CONSTRUCTION Page 2 October 10, 2020 Project No. 20-1106E6 The site location is shown on the attached Vicinity Map, Figure 1. The site is a rectangular-shaped, residential lot located on the east side of Roosevelt Street in the City of Carlsbad, California. The property is vacant. The lot slopes down gently to the west. Vegetation consists of sparse grass and a few shrubs and trees. The parcel is bordered by Roosevelt Street, on the west, an alley on the east and similar homes on the north and south. No building plans were available at the time of our investigation. It is our understanding that the proposed construction will consist of a two-story, single-family residence. The residence will be a wood framed building founded on continuous and/or individual spread footings with a slab-on- grade floor. SUBSURFACE EXPLORATION AND LABORATORY TESTING The subsurface exploration consisted of drilling three test borings to a maximum depth of 4 feet with a hand auger. The borings were drilled on September 17, 2020. The approximate locations of the test borings are shown on Figure 2. Logs of the test borings are presented on Figure 3. Following the subsurface exploration, laboratory testing was performed to evaluate the pertinent engineering properties of the foundation soils. The laboratory tests consisted of 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 the test borings, Figure 3 and on Figure 4, Results of Laboratory Tests. SUBSURFACE SOIL CONDIDONS The subsurface soil descriptions are 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, Figure 3. The following are general descriptions of the encountered soils: Topsoil: Topsoil was encountered to a depth of 1 foot in the test borings and consisted of dark brown, dry, loose and porous, silty sand with some small roots. Terrace Deposits: Terrace deposits were encountered beneath the topsoil at a depth of 1 foot, to the maximum depth explored of 4 feet. The terrace deposits consisted of reddish brown, dry to moist, medium dense to dense, silty sand. EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Geotechnical Investigation for Proposed Two-Story, Single-Family Residence 3460 Roosevelt Street Carlsbad, California 92008 SOIL PROPERTIES a. Compressible Soils Page3 October 10, 2020 Project No. 20-1106E6 Loose, compressible topsoil was encountered to a depth of approximately 1 foot within the area of the proposed construction. Footings for the proposed single-family residence should be extended through the topsoil into the underlying, medium dense to dense terrace deposits. b. Expansive Soils An expansion index test 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 encountered to the depths of the test borings. GEOLOGY From geologic maps published by the State of California, the site is underlain 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 residence 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 the attached Figure 5. CONCLUSIONS AND RECOMMENDATIONS Construction of the proposed single-family 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 single-family residence should be cleared of vegetation and other unsuitable materials, which should be properly disposed of off-site. The area should be EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Geotechnical Investigation for Proposed Two-Story, Single-Family Residence 3460 Roosevelt Street Carlsbad, California 92008 Page4 October 10, 2020 Project No. 20-1106E6 thoroughly inspected for buried objects that need to be rerouted or removed prior to construction. All holes, trenches, or loose soil pockets left by the removal of these objects should be properly backfilled with compacted fill soils. b. Removal and Recompaction of Loose Surface Soils Beneath Floor Slabs Beneath new floor slabs, the existing, loose topsoil should be removed and recompacted down to medium dense to dense terrace deposits, a depth of approximately 1 foot. Removal depths should be confirmed by our field representative. c. Compaction and Method of Filling All fill and trench backfill should be compacted to a rrurumum 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. 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 measures have been installed. After completion of grading, all excavated surfaces should exhibit positive drainage and eliminate areas where water might pond. TEMPORARY VERTICAL EXCAVATIONS Temporary vertical slopes and excavations should not exceed 5 feet. Any slopes and excavations greater than 5 feet in height should be shored or laid back at a 1 : 1 (horizontal to vertical) inclination. CAL-OSHA guidelines for temporary slopes and trench excavation safety should be implemented during construction. EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Geotechnical Investigation for Proposed Two-Story, Single-Family Residence 3460 Roosevelt Street Carlsbad, California 92008 FOUNDATIONS AND FLOOR SLABS Page 5 October 10, 2020 Project No. 20-1106E6 • Footings for the proposed two-story, single-family residence should be extended through the upper, loose topsoil and at least 6 inches into the underlying, medium dense to dense terrace deposits. Anticipated footing depths are approximately 1. 5 feet below existing grades but may be deeper. Actual footing depths should be determined during construction by our field representative. • Continuous footings should be at least 15 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 individual spread footings. This value may be increased by one-third for short term wind or seismic loads. 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 0.4 may also be used. If passive and friction values are used together, the friction value should be reduced by one-third. • Total and differential settlements of ½ inch may be assumed. • 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 28-day 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. DRAINAGE Adequate measures should be undertaken so that drainage water is directed away from foundations, footings, floor slabs and the tops of slopes via rain gutters, downspouts, surface swales and subsurface drains towards the natural drainage for this area. As required in the California Building Code, a minimum gradient of 2 percent is recommended in hardscape areas adjacent to the structure. In earth areas, a minimum gradient of 5 percent away from the structure for a distance of at least 10 feet should be provided. If this requirement cannot be met due to site limitations, EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Geotechnical Investigation for Proposed Two-Story, Single-Family Residence 3460 Roosevelt Street Carlsbad, California 92008 Page 6 October 10, 2020 Project No. 20-1106E6 drainage can be done through a swale in accordance with Section 1804. 4 of the California Building Code. Earth swales should have a minimum gradient of 2 percent. Drainage should be directed to approved drainage facilities. Proper surface and subsurface drainage will be required to minimize the potential of water seeking the level of the bearing soils under the foundations, footings and floor slabs, which may otherwise result in undermining and differential settlement of the structure and other improvements. 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 to be representative of site conditions; however, soil and geologic conditions may vary significantly between exploration trenches, boreholes 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 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 EAST COUNTY son, CONSULTATION AND ENGINEERING, INC. Geotechnical Investigation for Proposed Two-Story, Single-Family Residence 3460 Roosevelt Street Carlsbad, California 92008 Page 7 October 10, 2020 Project No. 20-1106E6 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. 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 3460 Roosevelt Street Carlsbad, California 92008 DOWNTOWN CARLSBAD I:... • S a: escrt - g .. cc s Sea~o ~ &. S~ea ... u FIGURE 1 VICINITY MAP BARRIO 9 3460 Roosevelt St, Carlsbad, CA 92008 NORTH BEACH ;tiers:r E eTer:a~, ~:i-,:,: Page 8 October 10, 2020 Project No. 20-1106E6 -,.. .,. ~.--A -...i.:: ~ .... ;l<w ~, d ag: .!9 EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Geotechnical Investigation for Proposed Two-Story, Single-Family Residence 3460 Roosevelt Street Carlsbad, California 92008 FIGURE 2 LOCATIONS OF TEST BORINGS LEGEND Page9 October 10, 2020 Project No. 20-1106E6 B-3 APPROXIMATE LOCATION OF TEST BORING EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Geotechnical Investigation for Proposed Two-Story, Single-Family Residence 3460 Roosevelt Street Carlsbad, California 92008 DEPTH Surface 1.0' 2.0' 3.0' DEPTH Surface 1.0' 2.0' 4.0' DEPTH Surface 1.0' 2.0' 2.5' FIGURE3 LOGS OF TEST BORINGS BORINGB-1 SOIL DESCRIPTION TOPSOIL dark brown, dry, loose, porous, silty sand with rootlets TERRACE DEPOSITS reddish brown, dry to moist, medium dense, silty sand reddish brown, dry to moist, dense, silty sand refusal, bottom of test boring, no caving, no groundwater test boring drilled and backfilled 9/17/2020 BORINGB-2 SOIL DESCRIPTION TOPSOIL dark brown, dry, loose, porous, silty sand with rootlets TERRACE DEPOSITS reddish brown, dry, medium dense, silty sand reddish brown, dry to moist, dense, silty sand refusal, bottom of test boring, no caving, no groundwater test boring drilled and backfilled 9/17/2020 BORING B-3 SOIL DESCRIPTION TOPSOIL dark brown, dry, loose, porous, silty sand with rootlets TERRACE DEPOSITS reddish brown, dry, dense, silty sand reddish brown, dry, dense, silty sand refusal, bottom of test boring, no caving, no groundwater test boring drilled and backfilled 9/17/2020 Y = DRY DENSITY IN PCF M = MOISTURE CONTENT IN % Page 10 October 10, 2020 Project No. 20-1106E6 y M y M 114.2 6.3 y M EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Geotechnical Investigation for Proposed Two-Story, Single-Family Residence 3460 Roosevelt Street Carlsbad, California 92008 FIGURE 4 LABO RA TORY TEST RES UL TS EXPANSION INDEX TEST (ASTM D 4829) TEST INITIAL SATURATED INITIAL EXPANSION LOCATION MOISTURE MOISTURE DRY INDEX CONTENT CONTENT(%) DENSITY (%) (PCF) B-1 @ 1.5' 9.4 18 .2 111.7 0 Page 11 October 10, 2020 Project No. 20-1106E6 EXPANSION POTENTIAL NON- EXPANSIVE EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Geotechnical Investigation for Proposed Two-Story, Single-Family Residence 3460 Roosevelt Street Page 12 October 10, 2020 Project No. 20-1106E6 Carlsbad, California 92008 FIGURE 5 SEISMIC DESIGN VALUES 3460 Roosevelt St, Carlsbad, CA 92008, USA Date Design Code Reference Document Risk Category Site Class Type Value Ss 1.078 S: 0.39 S\ls 1.152 s.,,: null -See Section 11.4.8 S::i, 0.768 S:n null -See Section 11.4.8 Type Value soc null -See Section 11.4.8 F. 1.069 Fv null -See Section 11.4.8 Description Description 10/8/2020. 3:02:37 PM ASCE7-16 II D -Stiff Soil MCE._ ground motion. (for 0.2 second period) CE, ground motion. {for 1.0s 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 Site amplification factor at 0.2 second Site amplification actor at LO second EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC.