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HomeMy WebLinkAboutCDP 2020-0027; MATTHEW RESIDENCE; GEOTECHNICAL INVESTIGATION FOR PROPOSED TWO-STORY, SINGLE FAMILY RESIDENCE, 5511 LOS ROBLES DRIVE, CARLSBAD CA 92008, APN 210-115-14; 2020-02-10Arvin & Sepideh Matthew 215 Montclair Drive Danville, California 94526 EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. 10925 HARTLEY ROAD, SUITE "I" SANTEE, CALIFORNIA 92071 TEL. (619) 258-7901 February 10, 2020 Project No. 20-1126G3 Subject: Geotechnical Investigation for Proposed Two-Story, Single-Family Residence 5511 Los Robles Drive Carlsbad, CA 92008 APN 210-115-14 Dear Mr. & Mrs. Matthew: In accordance with your request, we have performed a geotechnical investigation at the subject site to determine the geotechnical conditions and provide recommendations for design and construction of the proposed two-story, single-family residence. SCOPE OF SERVICES The following scope of work was performed for this investigation: 0 Site reconnaissance and review of published geologic, seismologic and geotechnical reports and maps pertinent to the project area 0 Subsurface exploration consisting of four test borings excavated within the limits 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 sealed in moisture-resistant containers and transported to the 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 5511 Los Robles Drive Carlsbad, CA 92008 APN 210-115-14 SITE DESCRIPTION AND PROPOSED CONSTRUCTION Page2 February 10, 2020 Project No. 20-1126G3 The site location is shown on the attached Vicinity Map, Figure 1. The site is a roughly rectangular-shaped, residential lot located at the northwest corner of Los Robles Drive and Manzano Drive, in the City of Carlsbad, California. The property is presently occupied by a one- story, single-family residence, an out building and a carport. The building pad is relatively level, while the rest of the site slopes gently down to the west and east. Vegetation consists of grass, shrubs and trees. The parcel is bordered by Los Robles Drive to the east, Manzano Drive to the south and other homes to the north and west. The preliminary plans prepared by Wright Designs of Carlsbad, California indicate that the proposed construction consists of a new, two-story residence. The existing residence will be demolished as part of the new construction. The new residence will be a wood framed structure founded on continuous and/or individual spread footings with a slab-on-grade floor. SUBSURFACE EXPLORATION AND LABORATORY TESTING Four test borings were excavated on January 29, 2020 to a maximum depth of approximately 6 feet below existing site grades with a hand auger. The approximate locations of the test borings are shown on the attached Figure 2. Logs of the subsurface materials are presented on Figure 3. Following the subsurface exploration, laboratory testing was performed on selected soil samples to evaluate the pertinent engineering properties of the foundation materials. 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 the test borings, Figure 3 and on the summary of laboratory test results, Figure 4. SUBSURFACE SOIL CONDITIONS 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 materials are presented on the logs of the test borings on Figure 3. The following are general descriptions of the encountered soils: Topsoil Topsoil was encountered in the test borings to a depth of approximately 1 foot and consisted of dark brown, dry, loose and porous, silty sand with some organics (rootlets). Terrace Deposits Terrace deposits were encountered in the test pits below the topsoil to the maximum depth explored of 6 feet. The terrace deposits generally consisted of 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 5511 Los Robles Drive Carlsbad, CA 92008 APN 210-115-14 SOIL PROPERTIES a. Compressible Soils Page 3 February 10, 2020 Project No. 20-1126G3 Our field observations and testing indicate low compressibility within the underlying terrace deposits. However, loose, compressible topsoil was encountered to a depth of approximately 1 foot below the existing ground surface. In addition, it is anticipated that the upper 1 foot of the terrace deposits will be disturbed by demolition and clearing of the existing foundations. As a result, the existing topsoil and upper 1 foot of the terrace deposits should be removed and recompacted to a minimum of 90 percent relative compaction, as discussed later in the report. b. Expansive Soils An expansion index test (ASTM D 4829) was performed on a representative sample of the terrace deposits. An expansion index of O was obtained which indicates the soils are non expansive. GROUNDWATER No groundwater was encountered in the test borings. 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 areas of the proposed construction should be cleared of vegetation, existing concrete foundations and deleterious materials. Vegetation and debris from the clearing operation should be properly disposed of off-site. The area should be thoroughly inspected for any possible buried objects that need to be rerouted or removed prior to construction. All holes, trenches, or pockets left by the removal of these objects should be properly backfilled with compacted fill materials. b. Surface Soil Removals The loose topsoil and upper 1 foot of the terrace deposits (to a minimum total depth of 2 feet) within building areas and to a distance of at least 5 feet outside building limits should be removed EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Geotechnical Investigation for Proposed Two-Story, Single-Family Residence 5511 Los Robles Drive Carlsbad, CA 92008 APN 210-115-14 Page 4 February 10, 2020 Project No. 20-1126G3 exposing the underlying, medium dense terrace deposits. Surface soil removals should include any soils disturbed by demolition and removal of the existing foundations . c. 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 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 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 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 SLOPES For the excavation of foundations and utility trenches, temporary vertical cuts to a maximum height of 5 feet may be constructed. Any temporary cuts greater than 5 feet in height should be shored or laid back at a 3/4: 1 (horizontal to vertical) slope ratio. CAL-OSHA guidelines for temporary slopes and trench excavation safety should be implemented during construction. EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Geotecbnical Investigation for Proposed Two-Story, Single-Family Residence 5511 Los Robles Drive Carlsbad, CA 92008 APN 210-115-14 FOUNDATIONS AND FLOOR SLABS Pages February 10, 2020 Project No. 20-1126G3 • Footings for the proposed two-story, single-family residence should be founded in properly compacted fill or medium dense terrace deposits. Footings should have a minimum depth of 18 inches below building pad grade or lowest adjacent, finished grade, whichever is deeper. • 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. • 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, the maximum concrete slump should be 4 inches and the maximum water- cement ratio should be 50 percent. Some shrinkage cracks are still possible. • 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 of ½ 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. • All footing excavations should be inspected and approved by our field representative. DRAINAGE Adequate measures should be undertaken so that drainage water is directed away from the foundations, footings, floor slabs and the tops of slopes via rain gutters, downspouts, surface swa1es and subsurface drains towards the natural drainage for this area. As required in the 2019 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, drainage can be done through a swale in accordance with Section 1804.4 of the 2016 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. EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Geotechnical Investigation for Proposed Two-Story, Single-Family Residence 5511 Los Robles Drive Carlsbad, CA 92008 APN 210-115-14 LIMITATIONS OF INVESTIGATION Page6 February 10, 2020 Project No. 20-1126G3 Our investigation was perfonned using the skill and degree of care ordinarily exercised, under similar circumstances, by reputable soils 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 perfonnance. 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, 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 infonnation 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. ADDffiONALSERVICES The 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 5511 Los Robles Drive Carlsbad, CA 92008 APN 210-115-14 Respectfully Submitted, Martin R. Owen, PE, GE Geotechnical Engineer Attachments: Figures 1 through 5 Page 7 February 10, 2020 Project No. 20-1126G3 EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Geotecbnical Investigation for Proposed Two-Story, Single-Family Residence 5511 Los Robles Drive Page8 February 10, 2020 Project No. 20-1126G3 Carlsbad, CA 92008 APN 210-115-14 C:l t ~ El FIGURE 1 VICINITY MAP 9 Ctly sr C..ir sbiJd 9 ~ Gr , f R, ,,, A r • \ ' \ ;, 1 Kr ri Grody Ford A ~ C;)•lsbod San Diego Y 9 9 '.:I ' 0- Cnr I' JCltOll S di k O'f•c.id S1,;hoo 9 5511 Los Robles Drive Canyon Btc;tles USA Q ' ' \ . • BJ s R tilu. rt \ &'Brew 1 1, t ' . ' '\ \ .. " Ro ,d Rinner Co rr1c,P olQ • \ PAC flC POI T n BUSINESS Ccn er T M lton s Craft Bake•s 9 EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. r-N Out [3 :::>r It R pu It Cc.rt bu To Geotechnical Investigation for Proposed Two-Story, Single-Family Residence 5511 Los Robles Drive Carlsbad, CA 92008 APN 210-115-14 FIGURE2 LOCATIONS OF TEST BORINGS LEGEND B-4 APPROXIMATE LOCATION OF TEST BORING Page9 February 10, 2020 Project No. 20-1126G3 EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Geotechnical Investigation for Proposed Two-Story, Single-Family Residence 5511 Los Robles Drive Carlsbad, CA 92008 APN 210-115-14 DEPTH Surface 1.0' 2.5' 4.0' DEPTH Surface 1.0' 3.0' 6.0' DEPTH Surface 1.0' 2.5' 5.0' FIGUREJ LOGS OF TEST BORINGS SOIL DESCRIPTION TOPSOIL BORING B-1 dark brown, moist, loose, silty sand with rootlets TERRACE DEPOSITS reddish brown, moist, medium dense, silty sand reddish brown, moist, dense, silty sand bottom of test boring, no caving, no groundwater test boring backfilled 1/29/2020 SOIL DESCRIPTION TOPSOIL BORING B-2 dark brown, moist, loose, silty sand with rootlets TERRACE DEPOSITS reddish brown, moist, medium dense, silty sand reddish brown, moist, dense, silty sand bottom of test boring, no caving, no groundwater test boring backfilled 1/29/2020 SOIL DESCRIPTION TOPSOIL BORING B-3 dark brown, moist, loose, silty sand with rootlets TERRACE DEPOSITS reddish brown, moist, medium dense, silty sand reddish brown, moist, dense, silty sand bottom of test boring, no caving, no groundwater test boring backfilled 1/29/2020 Y = DRY DENSITY IN PCF M = MOISTURE CONTENT IN% Page 10 February 10, 2020 Project No. 20-1126G3 y M 124.2 9.9 y M 113 .7 8.7 y M EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Geotechnical Investigation for Proposed Two-Story, Single-Family Residence 5511 Los Robles Drive Carlsbad, CA 92008 APN 210-115-14 DEPTH Surface 1.0' 2.5' 4.0' FIGURE3 LOGS OF TEST BORINGS (CONTINUED) SOIL DESCRIPTION TOPSOIL BORING B-4 dark brown, moist, loose, silty sand with rootlets TERRACE DEPOSITS reddish brown, moist, medium dense, silty sand reddish brown, moist, dense, silty sand bottom of test boring, no caving, no groundwater test boring backfilled 1/29/2020 Y = DRY DENSITY IN PCF M = MOISTURE CONTENT IN% Page 11 February 10, 2020 Project No. 20-1126G3 y M EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Geotechnical Investigation for Proposed Two-Story, Single-Family Residence 5511 Los Robles Drive Carlsbad, CA 92008 APN 210-115-14 FIGURE4 RESULTS OF LABORATORY TESTS EXPANSION INDEX TEST (ASTMD 4829 Page 12 February 10, 2020 Project No. 20-1126G3 TEST INITIAL SATURATED INITIAL EXPANSION EXPANSION LOCATION MOISTURE MOISTURE DRY INDEX POTENTIAL CONTENT CONTENT(%) DENSITY (%) (PCF) B-1 @ 2.0' 9.2 17 .7 112.8 0 NONE EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Geotechnical Investigation for Proposed Two-Story, Single-Family Residence 5511 Los Robles Drive Carlsbad, CA 92008 APN 210-115-14 FIGURES SEISMIC DESIGN VALUES 5511 Los Robles Dr, Carlsbad, CA 92008, USA Date Design Code Reference Document Risk Category Site Class Type Ss Type soc Value D 1.031 1.549 Value 1.172 0.451 1.209 0.698 0.806 0.466 Description Description MCE-ground motion. (for 0.2 second period) MCEs ground motion. (for l.Os 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 ca egor-; Site amplification factor at 0.2 second Site amplification factor at 1.0 second Page 13 February 10, 2020 Project No. 20-1126GJ 2/10/2020, 8:10:49 AM ASCE7-10 IJ D -Stiff Soil EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC.