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HomeMy WebLinkAboutPUD 2021-0006; ACACIA BEACH HOMES; GEOTECHNICAL INVESTIGATION; 2021-06-21GEOTECHNICAL INVESTIGATION Proposed Residential Development 245 Acacia A venue Carlsbad, California HETHERINGTON ENGINEERING, INC. HETHERINGTON ENGINEERING, INC. SOIL & FOUNDATION ENGINEERING • ENGINEERING GEOLOGY • HYDROGEOLOGY Rincon Homes/Rincon Real Estate Group 3005 S. El Camino Real San Clemente, California 92672 Attention: Subject: Mr. Tom St. Clair GEOTECHNICAL INVESTIGATION Proposed Residential Development 245 Acacia Avenue Carlsbad, California References: Attached Dear Mr. St. Clair: June 21, 2021 Project No. 9324.1 Log No. 21510 In accordance with your request, we have performed a geotechnical investigation for the proposed three, three-story detached single-family residences at the subject site. Our work was performed during May through July 2021. The purpose of the investigation was to evaluate the geologic and soil conditions at the site in order to provide grading and foundation recommendations for the proposed construction. Our scope of work included the following: • Research and review of readily available geologic literature, geotechnical reports and plans pertinent to the site (see References). • Subsurface exploration consisting of test pits to depths of 5.5 and 6.0-feet for the purpose of soil/bedrock sampling and geologic observation. • Laboratory testing of soil/bedrock samples obtained during the subsurface exploration. • Engineering and geologic analysis. • Preparation of a report providing the results of our field and laboratory work, analysis and our conclusions and recommendations. 5365 Avenida Encinas, Suite A• Carlsbad, CA 92008-4369 • (760) 931-1917 • Fax (760) 931-0545 333 Third Stree • Laguna Beach, CA 9265 • (949) 715-5440 • Fax (949) 715-5442 www. hetheri ngtoneng ineering. com GEOTECHNICAL INVESTIGATION Project No. 9324.1 Log No. 21510 June 21, 2021 Page 2 SITE DESCRIPTION The subject property is located at 245 Acacia Avenue, Carlsbad, California (see Location Map, Figure 1 ). The site consists of a relatively flat rectangular shaped parcel. The site presently supports two, single-story single-family structures. The property is bounded by Acacia A venue to the north, and by similarly developed residential properties to the south, west and east PROPOSED DEVELOPMENT Proposed development consists of three, three-story detached single-family residences. We anticipate wood-frame construction founded on conventional continuous/spread footings with slab-on-grade floors. Building loads are expected to be typical for this type of relatively light construction. Grading is expected to consist of cut and fill on the order of approximately 1 to 3-feet. SUB SURF ACE EXPLORATION Subsurface exploration consisted of two hand excavated test pits to maximum depths of 5.5 and 6.0-feet below existing grades. The approximate locations of the test pits are shown on the attached Plot Plan, Figure 2. The subsurface exploration was supervised by an engineer from this office, who visually classified the soil, and obtained bulk and relatively undisturbed samples for laboratory testing. The soils were visually classified according to the Unified Soil Classification System. Classifications are shown on the attached Logs of Test Pits, Figures 3 and 4. LABO RA TORY TESTING Laboratory testing was performed on samples obtained during the subsurface exploration. Tests performed consisted of the following: • Dry Density/Moisture Content (ASTM: D 2216) • Maximum Dry Density/Optimum Moisture Content (ASTM: D 1557) • Direct Shear (ASTM: D 3080) HETHERINGTON ENGINEERING. INC. I f PACIFIC OCEAN SITE ADAPTED FROM: The Thomas Guide, San Diego County, 57th Edition, Page 1106 LOCATION MAP HETHERINGTON ENGINEERING, INC. SCALE: 1" -2000' (1 Grid Equals: 0.5 x 0.5 miles) 245 Acacia Avenue Carlsbad California GEOTECHNICAL CONSULTANTS PROJECT NO. 9324.1 I FIGURE NO. 1 lfRI GEOTECHNICAL INVESTIGATION Project No. 9324.1 Log No. 21510 June21,2021 Page 3 • Soluble Sulfate (Cal Test 417) Results of the dry density and moisture content determinations are presented on the Logs of Test Pits, Figures 3 and 4. The remaining laboratory test results are presented on the attached Laboratory Test Results, Figure 5. SOIL AND GEOLOGIC CONDITIONS 1. Geologic Setting The subject site lies within a relatively level marine terrace that is contained within the coastal plain region of northern San Diego County, California. The coastal plain region is characterized by numerous regressive marine terraces of Pleistocene age that have been established above wave-cut platforms of underlying middle Eocene bedrock and were formed during glacio-eustatic changes in sea level. The terraces extend from areas of higher elevation east of the site and descend generally west- southwest in a "stair-step" fashion down to the present day coastline. These marine terraces increase in age eastward. The site area is contained within the southwest portion of the California Department of Conservation San Luis Rey 7-1/2 minute quadrangle (Reference 10). 2. Geologic Units a. Weathered Paralic Deposits: Weathered paralic deposits were observed to immediately underlie the property to a depth of approximately 1 to 3-feet below existing site grades. The weathered paralic deposits consist generally of dry to damp, medium dense to dense, brown silty sand. The existing weathered paralic deposits are not considered suitable for support of proposed improvements or compacted fill in their existing condition. b. Paralic Deposits: Underlying the weathered paralic deposits are sediments classified as Pleistocene paralic deposits. These sediments consist generally of damp, dense to very dense, orange brown silty sand. 3. Groundwater Groundwater or seepage was not encountered in the test pits to the maximum explored depths. It should be noted, however, that fluctuations in the amount and HETHERINGTON ENGINEERING, INC. GEOTECHNICAL INVESTIGATION Project No. 9324.1 Log No. 21510 June 21, 2021 Page 4 level of groundwater may occur due to variations in rainfall, irrigation, and other factors that might not have been evident at the time of our field investigation. SEISMICITY Based on our review of the available geologic maps/literature, there are no active or potentially active faults that traverse the subject site, and the property is not located within the currently mapped limits of an Alquist-Priolo Earthquake Fault Zone. The following table lists the known active faults that would have the most significant impact on the site: Maximum Probable Fault Earthquake Slip Rate (Moment Maenitude) (mm/year) Rose Canyon 6.9 1.5 (4.8-miles/7.7 kilometers southwest) Palos Verdes/Coronado Bank (20. 5-miles/3 3. 0-kilometers 7.7 3.0 southwest) SEISMIC EFFECTS 1. Ground Accelerations The most significant probable earthquake to affect the property would be a 7. 7 magnitude earthquake on the Palos Verdes/Coronado Bank fault. Based on Section 1803.5.12 of the 2016 California Building Code and Section 11.8.3 of ASCE 7-10, peak ground accelerations (PGAM) of 0.540g are possible for the design earthquake. 2. Landsliding Review of the referenced geologic maps/literature indicates that the subject property is not included within the limits of any previously mapped landsliding. The risk of seismically induced landsliding affecting the proposed structures is considered low due to the relatively level topography. HETHERINGTON ENGINEERING. INC. GEOTECHNICAL INVESTIGATION Project No. 9324.1 Log No. 21510 June 21, 2021 Page 5 3. Ground Cracks The risk of fault surface rupture due to active faulting is considered low due to the absence of a known active fault on site. Ground cracks due to shaking from seismic events in the region are possible, as with all of southern California. 4. Liquefaction The risk of seismically induced liquefaction within the site is considered low due to the dense nature of the terrace deposits and lack of shallow groundwater. 5. Tsunamis The site is not located within a mapped tsunami inundation area. The risk of a tsunami adversely impacting the site is considered low due to the elevation of the property above sea level. CONCLUSIONS AND RECOMMENDATIONS 1. General The proposed development is considered feasible from a geotechnical standpoint. Grading and foundation plans should take into account the appropriate geotechnical features of the site. Provided that the recommendations presented in this report and good construction practices are utilized during design and construction, the proposed construction is not anticipated to adversely impact the adjacent properties from a geotechnical standpoint. 2. Seismic Parameters for Structural Design Seismic considerations that may be used for structural design at the site include the following: a. Ground Motion -The proposed improvements should be designed and constructed to resist the effects of seismic ground motions as provided in Section 1613 of the 2019 California Building Code and ASCE 7-16. Site Address: 245 Acacia A venue, Carlsbad, CA 92008 Latitude: Longitude: 33.1519582 N 117.3462458 W HETHERINGTON ENGINEERING, INC. GEOTECHNICAL INVESTIGATION Project No. 9324.1 Log No. 21510 June21,2021 Page 6 b. Spectral Response Accelerations -Using the location of the property and data obtained from the SEAOC/OSHPD Seismic Design Maps Program, short period Spectral Response Accelerations Ss (0.2 second period) and S1 (1.0 second period) are: Ss = 1.094g S1 = 0.395g c. Site Class -In accordance with Chapter 20 of ASCE 7, and the underlying geologic conditions, a Site Class D is considered appropriate for the subject property. d. Site Coefficients Fa and Fv -In accordance with Table 1613.3.3 and considering the values of Ss and S1, Site Coefficients for a Class D site are: Fa= 1.062 Fv = null e. Spectral Response Acceleration Parameters Sms and Sm1 -In accordance with Section 1613.3.3 and considering the values of Ss and S1, and Fa and Fv, Spectral Response Acceleration Parameters for Maximum Considered Earthquake are: Sms = 1.162g Sm1 =null f. Design Spectral Response Acceleration Parameters Sds and Sd1 -In accordance with Section 1613.3.4 and considering the values ofSms and Sm1,Design Spectral Response Acceleration Parameters for Maximum Considered Earthquake are: Sds = 0.775g Sd1 = null g. Long Period Transition Period -A Long Period Transition Period of TL = 8 seconds is provided for use in San Diego County. h. Seismic Design Category -In accordance with Tables 1604.5, 1613.3.5(1) and 1613.3.5(2), and ASCE 7, a Risk Category II and a Seismic Design Category D are considered appropriate for the subject property. HETHERINGTON ENGINEERING. INC. GEOTECHNICAL INVESTIGATION Project No. 9324.1 Log No. 21510 June 21, 2021 Page 7 3. Site Grading Prior to grading, areas of proposed improvements should be cleared of existing surface improvements, obstructions, vegetation and debris. Materials generated during clearing should be disposed of at an approved location off-site. Holes resulting from the removal of buried obstructions should be filled with compacted fill or lean concrete. Seepage pits and/or septic systems, if encountered during site development, should be abandoned in accordance with local guidelines. Within the limits of proposed improvements and to 3-feet beyond, any ex1stmg fill/weathered paralic deposits should be removed down to approved undisturbed paralic deposits. We anticipate removal depths on the order of 1 to 3-feet below existing site grades. Actual removal depths should be determined in the field by the Geotechnical Consultant based on conditions exposed during grading. Following removals, the exposed surface soils should be scarified to a depth of 6 to 8- inches, moisture conditioned to about optimum moisture content and compacted to at least 90-percent relative compaction (ASTM: D 1557). Fill should be moisture conditioned to about optimum moisture content and compacted by mechanical means in uniform horizontal lifts of 6 to 8-inches in thickness. All fill should be compacted to a minimum relative compaction of 90- percent based upon ASTM: D 1557. The on-site materials are suitable for use as compacted fill provided all vegetation and debris are removed. Rock fragments over 6-inches in dimension and other perishable or unsuitable materials should be excluded from the fill. All grading and compaction should be observed and tested as necessary by the Geotechnical Consultant. 4. Foundation and Slab Recommendations The proposed improvements should be supported on conventional continuous/spread footings founded at least 18-inches into compacted fill and/or approved paralic deposits. Continuous footings should be at least 12-inches wide, and reinforced with a minimum of four #4 bars, two top and two bottom. Foundations located adjacent to utility trenches should extend below a 1: 1 (horizontal to vertical) plane projected upward from the bottom of the trench. HETHERINGTON ENGINEERING, INC. GEOTECHNICAL INVESTIGATION Project No. 9324.1 Log No. 21510 June 21, 2021 Page 8 Foundations bearing as recommended may be designed for a dead plus live load bearing value of 2000-pounds-per-square-foot. This value may be increased by one- third for loads including wind and seismic forces. A lateral bearing value of 250- pounds-per-square-foot per foot of depth and a coefficient of friction between foundation soil and concrete of 0.35 may be assumed. These values assume that footings will be poured neat against the foundation soils. Footing excavations should be observed by the Geotechnical Consultant prior to the placement of reinforcing steel in order to verify that they are founded in suitable bearing materials. Total and differential settlement due to foundation loads is considered to be less than 3/4 and 3/8-inch, respectively, for foundations founded as recommended. Slab-on-grade floors should have a minimum thickness of 5-inches and should be reinforced with #4 bars spaced at 18-inches, center-to-center, in two directions, and supported on chairs so that the reinforcement is at mid-height in the slab. Floor slabs should be underlain with a moisture vapor retarder consisting of a minimum 15-mil membrane. At least 2-inches of sand should be placed over the vapor retarder to assist in concrete curing and at least 2-inches of sand should be placed below the vapor retarder. The vapor retarder should be placed in accordance with ASTM: E 1643. Prior to placing concrete, the slab subgrade soils should be thoroughly moistened. Vapor retarders are not intended to provide a waterproofing function. Should moisture vapor sensitive floor coverings be planned, a qualified consultant/contractor should be consulted to evaluate moisture vapor transmission rates and to provide recommendations to mitigate potential adverse impacts of moisture vapor transmissions on the proposed flooring. 5. Sulfate Content A representative sample of the on-site soil was submitted for sulfate testing. The results of the sulfate content test are summarized on the Laboratory Test Results, Figure 5. The sulfate content is consistent with a not applicable (SO) sulfate exposure classification per Table 4.2.1 of the American Concrete Institute Publication 318, consequently, no special provisions for sulfate resistant concrete are considered necessary. Other corrosivity testing has not been performed, consequently, on-site soils should be assumed to be severely corrosive to buried metals unless testing is performed to indicate otherwise. HETHERINGTON ENGINEERING, INC. GEOTECHNICAL INVESTIGATION Project No. 9324.1 Log No. 21510 June 21, 2021 Page 9 6. Retaining Walls Retaining wall foundations should be designed in accordance with the foundation recommendations provided previously in this report. Retaining walls free to rotate (cantilevered walls) should be designed for an active pressure of 35-pounds-per- cubic-foot (equivalent fluid pressure). Walls restrained from movement at the top should be designed for an at-rest pressure of 55-pounds-per-cubic-foot (equivalent fluid pressure). These values are based on level backfill consisting of onsite granular soils. Any additional surcharge pressures behind retaining walls should be added to these values. Retaining walls should be provided with adequate drainage to prevent buildup of hydrostatic pressure and should be adequately waterproofed. The subdrain system behind retaining walls should consist at a minimum of 4-inch diameter Schedule 40 (or equivalent) perforated (perforations "down") PVC pipe embedded in at least 1- cubic-foot of 3/4-inch crushed rock per lineal foot of pipe all wrapped in an approved filter fabric. The subdrain system should be connected to a solid outlet pipe with a minimum of I-percent fall that discharges to a suitable drainage device. Recommendations for wall waterproofing should be provided by the Project Architect and/or Structural Engineer. The lateral pressure on retaining walls due to earthquake motions ( dynamic lateral force) should be calculated as PA = 3/8 y H2kh where PA = dynamic lateral force (pounds/foot) y = unit weight= 110-pounds-per-cubic-foot H = height of wall (feet) kh seismic coefficient= 0.18 The dynamic lateral force may also be expressed as 15-pounds-per-cubic-foot ( equivalent fluid pressure). The dynamic lateral force is in addition to the static force and should be applied as a triangular distribution at 1/3H above the base of the wall. The dynamic lateral force need not be applied to retaining walls 6-feet or less in height. HETHERINGTON ENGINEERING, INC. GEOTECHNICAL INVESTIGATION Project No. 9324.1 Log No. 21510 June 21, 2021 Page 10 7. Temporary Slopes Temporary slopes necessary to facilitate construction may be cut vertically in terrace deposits up to 5-feet where the cuts are not influenced by existing property line constraints or structures/improvements. Temporary slopes near existing structures/improvements/property lines, over 5-feet in height, and/or cuts exposing fill should be inclined at a slope ratio no steeper than 1: 1 (horizontal to vertical) or shored. Field observations by the Engineering Geologist during grading of temporary slopes are recommended and considered necessary to confirm anticipated conditions and provide revised recommendations if warranted. Shoring recommendations can be provided on request. 8. Retaining Wall and Utility Trench Backfill All retaining wall and utility trench backfill should be compacted to at least 90- percent relative compaction (ASTM: D 1557). Backfill should be tested and observed by the Geotechnical Consultant. 9. Site Drainage The following recommendations are intended to m1mm1ze the potential adverse effects of water on the structures and appurtenances. a. Consideration should be given to providing the structures with roof gutters and downspouts that discharge to an area drain system and/or to suitable locations away from the structure. b. All site drainage should be directed away from the structures. c. No landscaping should be allowed against buildings. Moisture accumulation or watering adjacent to foundations can result in deterioration of building materials and may effect foundation performance. d. Irrigated areas should not be over-watered. Irrigation should be limited to that required to maintain the vegetation. Additionally, automatic systems must be seasonally adjusted to minimize over-saturation potential particularly in the winter (rainy) season. HETHERINGTON ENGINEERING, INC. GEOTECHNICAL INVESTIGATION Project No. 9324.1 Log No. 21510 June 21, 2021 Page 11 e. All yard and roof drains should be periodically checked to verify they are not blocked and flow properly. This may be accomplished either visually or, in the case of subsurface drains, by placing a hose at the inlet and checking the outlet for flow. 10. Recommended Observation and Testing During Construction The following tests and/or observations by the Geotechnical Consultant are recommended: a. Observation and testing of grading. b. Foundation excavations prior to placement of forms and reinforcement. c. Utility trench backfill. d. Retaining wall backdrains and backfill. 11. Grading and Foundation Plan Review Grading and foundation plans should be reviewed by the Geotechnical Consultant to confirm conformance with the recommendations presented herein or to modify the recommendations as necessary. LIMITATIONS The analyses, conclusions and recommendations contained in this report are based on site conditions as they existed at the time of our investigation and further assume the excavations to be representative of the subsurface conditions throughout the site. If different subsurface conditions from those encountered during our exploration are observed or appear to be present in excavations during construction, the Geotechnical Consultant should be promptly notified for review and reconsideration of recommendations. Our investigation was performed using the degree of care and skill ordinarily exercised, under similar circumstances, by reputable Geotechnical Consultants practicing in this or similar localities. No other warranty, express or implied, is made as to the conclusions and professional advice included in this report. HETHERINGTON ENGINEERING. INC. GEOTECHNICAL INVESTIGATION Project No. 9324.1 Log No. 21510 June 21, 2021 Page 12 This opportunity to be of service is sincerely appreciated. If you have any questions, please call this office. Sincerely, HETHERINGTON E Civil Engineer , Geotechnical ( expires 3/31/ Jose Pimentel Engineer-in-Training Attachments: Location Map Plot Plan Logs of Test Pits Laboratory Test Results Edwin R. Cunningha Civil Engineer 81687 ( expires 3/31/22) Figure 1 Figure 2 Figures 3 and 4 Figure 5 Distribution: I-via e-mail Tom St. Clair (tstclair@rincongrp.com) 4-Addressee HETHERINGTON ENGINEERING, INC. REFERENCES 1) American Society of Civil Engineers/Structural Engineers Institute, "Minimum Design Loads for Buildings and Other Structures," ASCE 7-10, dated May 2010. 2) California Geological Survey, "Tsunami Inundation Map for Emergency Planning- San Luis Rey Quadrangle," dated June 1, 2009. 3) ICBO, California Building Code, 2016 Edition. 4) Stephen Dalton Architects, Floor Plans, dated May 24, 2021 (Sheets A2-1, A2-2, A2- 3). 5) Peterson, Mark P., et al, "Documentation for the 2008 Update of the United States National Seismic Hazards Maps," USGS Open File Report 2008-1128, dated 2008. 6) SEAOC/OSHPD Seismic Design Maps Website. 7) Tan, Siang S. and Kennedy, Michael P., "Geologic Maps of the Northwestern Part of San Diego County, California," California Division of Mines and Geology, Open-File Report 96-02, dated 1996. 8) Tan, Siang S. and Giffen, Desmond G., "Landslide Hazards in the Northern Part of the San Diego Metropolitan Area, San Diego, California," California Division of Mines and Geology, Open File Report 95-04, dated 1995. 9) California Department of Conservation-Division of Mines and Geology, "Geologic Maps of the Northwestern Part of San Diego County, California-Plate 1," dated 1996. 10) United States Geological Survey, "San Luis Rey Quadrangle-San Diego County 7.5- Minute Series," dated 2015. HETHERINGTON ENGINEERING. INC. Project No. 9324.1 Log No. ~ ($'. ;~ 0 2 0 5 10 15 20 LEGEND TP-1~ APPROXIMATE LOCATION OF TEST PIT PLOT PLAN HETHERINGTON ENGINEERING, INC. GEOTECHNICAL CONSULTANTS 245 Acacia A, Carlsbad, Cali PROJECT NO . 9324.1 I Fl( BACKHOE COMPANY: Mansolf Excavation BUCKET SIZE: DATE: 06/17/21 :,.., :,.., ::r: E-< r,:i E-< E-< E-< r,:i HH H - P. r,:i :,.:: P. (/) E-< (/) 4-1 r,:i µ. 5~ z (/) :,.., z u Cl -r,:i r,:i c:r: r,:i 0. Ill CJl Cl E-< Cl Cl -0.0 99 103 109 10.0 15.0 20.0 (/) -(/) r,:i .a: (/) c:r: E-< H :::, z uu E-< r,:i (/) E-< H CJl HZ-H 0 0 o\0 0:::, ::8 u -(/) - 3.0 SM 3.3 4.2 SOIL DESCRIPTION TEST PIT NO. TP-1 ELEVATION: I + WEATHERED PARALIC DEPOSITS: Brown silty sand, dry to damp, dense PARALIC DEPOSITS: Orange brown silty sand, damp, dense to very dense Total Depth: 5.5-feet No Groundwater No Caving LOG OF TEST PITS HETHERINGTON ENGINEERING, INC. 245 Acacia Avenue Carlsbad, California GEOTECHNICAL CONSULTANTS PROJECT NO. 9324.1 \ FIGURE NO. 3 BACKHOE COMPANY: Mansolf Excavation BUCKET SIZE: DATE: 06/17/21 :,-, :,-, :i:: E-< w E-< E-< E-< w ...:I H H - 0.. w :,:: 0.. C/l E-< C/l 4-l wi:... :3~ z C/l :,-, z u Cl-WW 0::: w 0. ca C/l C) E-< C) C) -0.0 105 108 10.0 15.0 20.0 C/l -C/l w <t: C/l 0::: E-< ...:I ::J z uu E-< w C/l E-< ...:I C/l HZ-H 0 0 01° 0 ::J :,:: u -C/l - 3.0 SM 5.6 SOIL DESCRIPTION TEST PIT NO. TP-2 ELEVATION: I WEATHERED TERRACE DEPOSITS: Brown silty sand, dry to damp, dense to very dense + PARALIC DEPOSITS: Orange brown silty sand, damp, dense to very dense @ 3': No recovery of Drive Sample Total Depth: 6-feet No Groundwater No Caving LOG OF TEST PITS HETHERINGTON ENGINEERING, INC. 245 Acacia Avenue Carlsbad, California GEOTECHNICAL CONSULTANTS PROJECT NO. 9324.1 I FIGURE NO. 4 LABORATORY TEST RESULTS DIRECT SHEAR (ASTM: D 3080) Sample Location Angle of Internal Cohesion (psf) Remarks Friction (0) TP-1 @ 0'-l' 34 50 2.5 -in. ring, remolded to 90%, soaked, consolidated, drained SULFA TE TEST RES UL TS (CAL 417) Sample Location I Soluble Sulfate in Soil(%) Sample Location TP-1 @ 0' to l ' TP-1@ 0' to 1' I 0.045 MAXIMUM DRY DENSITY/OPTIMUM MOISTURE CONTENT (ASTM: D 1557A) Description Maximum Dry Density ( ocf) Brown silty sand 125.0 HETHERINGTON ENGINEERING, INC. Optimum Moisture Content(%) 9.5 Figure 5 Project No. 9324.1 Log No.