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HomeMy WebLinkAboutCDP 04-52; Gorszwick Residence; Geotechnical Investigation; 2004-11-11i„^ I, I GEOTECHNICAL INVESTIGATION Proposed Retaining Wall/Rear Yard Fill 4237 Clearview Drive APN 207-085-07-00 Carlsbad, Califomia RECEIVED I Uil 0 7 2005 o IU z o < HETHERII«GTOI« ENGIIUEERIIU6, INC. HETHERINGTON ENGINEERING, INC. SOIL & FOUNDATION ENGINEERING • ENGINEERING GEOLOGY • HYDROGEOLOGY November 11,2004 Project No. 4865.1 Log No. 8648 Mr. Erick Gorszwick 4237 Clearview Drive Carlsbad, Califomia 92008 Subject: GEOTECHNICAL INVESTIGATION Proposed Retaining Wall/Rear Yard Fill 4237 Clearview Drive APN 207-085-07-00 Carlsbad, Califomia References: Attached Dear Mr. Gorszwick: In accordance with your request, Hetherington Engineering, Inc. has perfomied a geotechnical investigation at the subject site. Our work was performed in September throush November 2004. The purpose of our investigation was to evaluate geologic and soil conditions within the rear yard area in order to provide foundation recommendations for a proposed retaining wall and to determine the relative compaction of fill recently placed in the rear yard without the benefit of a grading pemiit or geotechnical observation/testing. With the above in mind, our scope of work included the following: • Research and review of available plans and geologic literature pertinent to the site vicinity (see References). • Subsurface exploration consisting of five exploratory test pits for soil/TDedrock sampling and geologic observation. • Laboratory testing of samples obtained from the subsurface exploration. • Engineering and geologic analysis. • Preparation of this report providing the results of our field and laboratory work, analyses, and our conclusions and recommendations. 5205 Avenida Encinas, Suite A • Carlsbad, CA 92008-4369 • (760) 931-1917 • Fax (760) 931-0545 32242 Paseo Adelanto, Suite C • San Juan Capistrano, CA 92675-3610 • (949) 487-9060 • Fax (949) 487-9116 www.hetheringtonengineering.conn GEOTECHNICAL INVESTIGATION ProjectNo. 4865.1 Log No. 8648 November 11, 2004 Page 2 SITE DESCRIPTION The subject property is located at 4237 Clearview Drive, within the Carisbad Highlands area of the city of Carisbad, Califomia (see Location Map, Figure 1). The site consists of a gently sloping, west-facing, rectangular-shaped lot. The lot presently supports a one- story, single-family residence with attached garage apparently supported by conventional continuous/spread footings with both slab-on-grade and raised floors. The rear yard contains a swimming pool and concrete decks. The property is bounded on the north, west and south by developed residential properties and to the east by Clearview Drive. SITE HISTORY Street improvements for the Carlsbad Highlands area were constmcted in 1951. The single-story residence was constmcted circa 1954 on an essentially natural slope, with grading apparently limited to excavation for a small daylight basement under the southem portion of the stmcture. Sometime after constmction, additional grading was performed in the rear yard for constmction of a swimming pool and adjacent decking. Beyond the limits ofthe pool and decking, the rear yard topography remained essentially unchanged. Grading, consisting of placement of fill, performed over the past approximately one year in the rear yard has created a level yard area. This fill extends essentially from the rear and side yard property lines east toward the swimming pool and house. The fill has a maximum estimated thickness of 6-feet at the southwesterly comer and thins out toward the east. Fill slopes are inclined at a 1:1 (horizontal to vertical) gradient. The toes of the fill slopes are within one to two feet of the rear and side property lines. On July 13, 2004, the city of Carlsbad issued a stop-work order and site grading ceased. PROPOSED DEVELOPMENT A retaining wall is proposed to retain the perimeter of the rear yard fill. SUBSURFACE EXPLORATION Subsurface conditions were explored by manually excavating five test pits to depths of approximately 6-feet below existing site grades. The approximate locations of the test pits are shown on the attached Plot Plan, Figure 2. The subsurface exploration was supervised by a geologist from this office, who visually classified the soil and bedrock materials, performed in-place density tests (ASTM: D HETHERINGTON ENGINEERiNG, INC. ADAPTED FROM: The Thomas Guide, San Diego County, 2004 Edition 1 N I SCALE: 1"-2000' (1 Grid = 0.5 x 0.5 miles) LOCATION MAP HETHERINGTON ENGINEERING, INC. GEOTECHNICAL CONSULTANTS 4237 Clean/lew Drive Carlsbad. California HETHERINGTON ENGINEERING, INC. GEOTECHNICAL CONSULTANTS PROJECTNO. 4865.1 FIGURE NO. 1 GEOTECHNICAL INVESTIGATION ProjectNo. 4865.1 Log No. 8648 November 11, 2004 Page 3 1556 and ASTM: D 2922) and obtained bulk samples for laboratory testing. The soils were visually classified according to the Unified Soil Classification System. Soil classifications are shown on the attached Logs of Test Pits, Figures 3 through 5. LABORATORY TESTING Laboratory testing was performed on samples obtained during the subsurface exploration. Tests performed consisted of the following: • Moisture Content (ASTM: D 2216) • Direct Shear (ASTM: D 3080) • Sulfate Content (EPA 9038) • Maximum Dry Density/Optimum Moisture Content (ASTM: D 1557-OOA) Results of the dry density and moisture content determinations are presented on the Logs of Test Pits, Figures 3 through 5. The remaining laboratory test results are presented on the Laboratory Test Results, Figure 6. SOIL AND GEOLOGIC CONDITIONS 1. Geologic Setting The subject site lies within the coastal plain region of northem San Diego County, Califomia. The coastal plain is characterized by numerous regressive marine terraces of Pleistocene age that have been established above wave-cut platforms of the underlying Eocene bedrock and were formed during glacio-eustatic changes in sea level. The terraces extend from areas of higher elevation approximately 2-miles east of the site and descend generally west-southwest in a "stairstep" fashion down to the present day coastline, with the age of the terraces decreasing from east to west. The site area is contained within the central eastem portion of the USGS San Luis Rey 7- 1/2 minute quadrangle. Based on the results of our investigation, the subject site is underlain by continental terrace deposits that essentially mantle the Pleistocene wave cut terrace surfaces. HETHERINGTON ENGINEERING, INC. GEOTECHNICAL INVESTIGATION ProjectNo. 4865.1 Log No. 8648 November 11, 2004 Page 4 2. Geologic Units a. Fill - The rear yard portion of the property is mantled by approximately 0 to 6- feet of recently placed fill consisting of damp to moist, loose to medium dense, light to dark reddish brown, gravelly silty to clayey fine to medium grained sand. The relative compaction of the fill ranges from 64 to 76-percent based on our testing. The approximate limits of the recently placed fill are shown on the attached Plot Plan, Figure 2. The fill deepens from east to west. b. Topsoil Overlying the terrace deposits is an approximately 1 to 2-feet thick topsoil layer consisting of light gray brown silty sand. c. Terrace Deposits - Continental terrace deposits encountered in our exploratory test pits and underlying the fill and topsoil consist generally of damp to moist, dense to very dense, reddish brown silty fine sand. 3. Groundwater No seepage or static groundwater was encountered in the exploratory test pits. It should be noted, however, that fluctuations in the amount and level of groundwater may occur due to variations in rainfall, irrigation, and other factors that may not have been evident at the time of our fleld investigation. SEISMICITY The site is located within the seismically active southem Califomia region. There are, however, no known active or potentially active faults presently mapped that pass through the site. Active fault zones within the general site region include the Rose Canyon/Newport-Inglewood, Elsinore and Coronado Bank/Palos Verdes Hills. Strong ground motion could also be expected from earthquakes occurring along the San Jacinto and San Andreas fault zones, which lie northeast ofthe site at greater distances, as well as a number of other offshore fauhs. The following table lists the known active faults that would have the most significant impact on the site: HETHERINGTON ENGINEERING, INC. GEOTECHNICAL INVESTIGATION ProjectNo. 4865.1 Log No. 8648 November 11, 2004 Page 5 Fault Maximum Probable Earthquake (Moment Magnitude) Slip Rate (mm/year) Fault Type Rose Canyon/Newport-Inglewood 9.5-kilometers (5.8 miles SW) 6.9 1.5 B Elsinore (Julian Segment) 3 6.5-kilometers (22.5.4-miles NE) 6.8 5 B Coronado Bank/Palos Verdes Hills 39-kilometers (24 miles SW) 7.4 3 B SEISMIC EFFECTS 1. Ground Accelerations 2. The most significant probable earthquake to affect the property would be a 6.9 magnitude earthquake on the Rose Canyon/Newport-higlewood fault zone. Depiction of probabilistic seismic hazard analysis utilizing a consensus of historical seismic data and the respective regional geologic conditions that are shown on the "The Revised 2002 Califomia Probabihstic Seismic-Hazard Maps" (Reference 2) indicates that peak ground accelerations of about 0.20 to 0.30g are possible with a 10% probability of being exceeded in 50-years. Ground Cracks The risk of surface fault mpture due to active faulting is considered low due to the absence of known active faulting on site. Ground cracks due to shaking from seismic events in the region are possible, as with all of southem Califomia. 3. Landsliding The risk of seismically induced landsliding affecting the proposed retaining wall is considered negligible due to the gentle topography of the property in the area of the retaining wall. HETHERINGTON ENGINEERING, INC. GEOTECHNICAL INVESTIGATION ProjectNo. 4865.1 Log No. 8648 November 11, 2004 Page 6 4. Liquefaction The risk of liquefaction is considered low due to the lack of a shallow groundwater table and dense underlying terrace deposits. 5. Tsunamis Due to the relatively high elevation of the site location above sea level, the potential for seismically generated ocean waves to affect the site is very low. CONCLUSIONS AND RECOMMENDATTONS 1. General The proposed retaining wall to support the rear yard fill wedge is considered feasible from a geotechnical standpoint. Foundation plans should consider the appropriate geotechnical features of the site. The proposed constmction is not anticipated to adversely impact the adjacent properties from a geotechnical standpoint assuming the recommendations presented in this report and good constmction practices" are implemented during design and constmction. The recently placed rear yard fill is poorly compacted and placed over topsoil; consequently, the fill is not considered a stmctural fill and is not suitable to support improvements. Long term differential settiement ofthe fill should be anticipated. 2. Seismic Parameters for Stmctural Design Seismic considerations that should be used for stmctural design at the site include the following: a. Ground Motion - The proposed retaining wall should be designed and constmcted to resist the effects of seismic ground motions as provided in Chapter 16, Division IV-Earthquake Design of the 2001 Califomia Building Code. The basis for the design is dependent on and considers seismic zoning, site characteristics, occupancy, configuration, stmctural system and building height. b. Soil Profile Type - In accordance with Section 1629.3.1, Table 16-J, and the underlying geologic conditions, a site Soil Profile of Type SD is considered appropriate for the subject property. HETHERINGTON ENGINEERING, INC. 1 GEOTECHNICAL INVESTIGATION ProjectNo. 4865.1 Log No. 8648 November 11, 2004 Page 7 c. Seismic Zone - hi accordance with Section 1629.4.1 and Figure 16-2, the subject site is situated within Seismic Zone 4. d- Seismic Zone Factor (z) - A Seismic Zone Factor of 0.40 is assigned based on Table 16-L Since the site is within Seismic Zone 4, Section 1629.4.2 requires a Seismic Source Type and Near Source Factor. e. Near-Source Factor (Na and Nv) - Based on the known active faults in the region and distance of the faults from the site, a Seismic Source Type of B per Table 16- U, and Near Source Factors of Na = 1.0 per Table 16-S and Nv = 1.0 per Table 16-T are provided. f. Seismic Coefficients (Ca and Cv) - Using the Soil Profile Type and Seismic Zone Factor along with Tables 16-Q and 16-R, the Seismic Coefficients Ca = 0.44 (Na) and Cv = 0.64 (Nv) are provided, or Ca = 0.44 and Cv = 0.64. 3. Retaining Walls The proposed retaining wall may be supported on conventional continuous footings founded at least 18-inches into approved terrace deposits. Continuous footings should be at least 15-inches wide and reinforced with a minimum of four #4 bars, two top and two bottom. New foundations located adjacent to utility trenches should extend to below a 1:1 plane projected upward from the bottom ofthe trench. 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-squarcTfoot per foot of depth and a coefficient of fiiction 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. Retaining walls free to rotate (cantilevered walls) should be designed for an active pressure of 40-pounds-per-cubic foot (equivalent fluid pressure) assuming level backfill consisting of the on-site soils. Walls restrained from movement at the top should be designed for an additional uniform soils pressure of 8xH pounds per square foot where H is the height of the wall in feet. Any additional surcharge pressure behind the wall should be added to these values. Retaining walls should be provided with adequate drainage to prevent buildup of hydrostatic pressure and should be HETHERINGTON ENGINEERING, INC. GEOTECHNICAL INVESTIGATION ProjectNo. 4865.1 Log No. 8648 November 11,2004 Page 8 adequately waterproofed. The subdrain system behind retaining walls should consist of at least 4-inch diameter Schedule 40 (or equivalent) perforated (perforations down) PVC pipe embedded in at least 1-cubic-foot of 3/4 inch cmshed rock per lineal foot of pipe all wrapped in approved filter fabric. Recommendations for wall waterproofing should be provided by the project Architect and/or Stmctural Engineer. 4. Temporarv Slopes Temporary slopes necessary to facilitate the constmction of the proposed retaining wall should be inclined at a ratio no steeper than 1:1 (horizontal to vertical) or shoring will be necessary. Field observations by the Engineering Geologist during grading of temporary slopes is recommended and considered necessary to confirm anticipated conditions and to provide revised recommendations if necessary. 5. Retaining Wall Backfill All retaining wall backfill should be compacted to at least 90-percent relative compaction based upon ASTM: Dl557-00 and the backfill should be observed and tested by the Geotechnical Consultant. 6. Sulfate Content A representative sample of the on-site soils was submitted for sulfate analyses. The result of the soluble sulfate test per EPA 9038 methods was 0.0299 percent. The sulfate content is consistent with a negligible exposure classification in Table 19-A-4 ofthe 2001 Cahfomia Building Code, consequently, sulfate resistant concrete is not considered necessary. 7. Recommended Observation and Testing During Constmction The following tests and/or observations by the Geotechnical Consultant are recommended: a. Foundation excavations prior to placement of forms and reinforcing steel. b. Retaining wall backdrain and backfill. HETHERINGTON ENGINEERING, INC. GEOTECHNICAL INVESTIGATION Project No. 4865.1 Log No. 8648 November 11, 2004 Page 9 8. Foundation Plan Review Foundation plans should be reviewed by the Geotechnical Consultant to confinn 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, the Geotechnical Consultant should be promptly notified for review and reconsideration ofthe 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. This oppormnity to be of service is sincerely appreciated. If you have any questions, please call this office. Sincerely, Hetherington Engineering, Inc. Jason S. Geldi Civil Enginee (expires 9/3 O/i Distribution: 4-Addre, Michel Vasconcellos Project Geologist Attachments: Location Map Plot Plan Logs of Test Pits Laboratory Test Results Figure 1 Figure 2 Figures 3 through 5 Figure 6 HETHERINGTON ENGINEERING, INC. REFERENCES 1. Califomia Division of Mines and Geology, "Geologic Maps of the Northwestem Part of San Diego County, Califomia, Oceanside, San Luis Rey, San Marcos, Encinitas and Rancho Santa Fe 7.5' Quadrangles," Plate 1, Open-File Report 96- 02, dated 1996. 2. Cao, Tianging, et al "The Revised 2002 Califomia Probabilistic Seismic Hazard Maps," dated June 2003. 3. City of Carlsbad, "Grading Ordinance Violation of Property Located at 4237 Clearview Drive, APN 207-085-07-00" dated July 13, 2004 4. ICBO, "CaUfomia Building Code," 2001 Edition. 5. ICBO, "Maps of Known Active Fault Near-Source Zones in Califomia and Adjacent Portions of Nevada," dated Febmary 1998. 6. Jennings, Charles W., "Fault Activity Map of Califomia and Adjacent Areas," Califomia Data Map Series, Map No. 6, dated 1994. 7. Peterson, M., Beeby, W., Bryant, W., et al., "Seismic Shaking Hazard Maps of Califomia," Califomia Division of Mines and Geology, Map Sheet 48, dated 1999. HETHERINGTON ENGINEERING, INC. ] ] ] ] ] ] ] TP-2 TP-4, /JTP-3 > 5 Q HI > < IU o CO 10 30 40 APPROXIMATE LIMITS OF -UNDOCUMENTED FILL LEGEND TP-5 n APPROXIMATE LOCATION OF TEST PIT PLOT PLAN HETHERINGTON ENGINEERiNG, INC. GEOTECHNiCAL CONSULTANTS 4237 Clearview Drive Carlsbad, Califomia PROJECT NO. 4865.1 FIGURE NO. j J ] BACKHOE COMPANY: Mansolf Excavation BUCKET SIZE: Hand Pit DATE: 09/30/04 SOIL DESCRIPTION TEST PIT NO. TP-1 ELEVATION: + TOPSOIL: Light gray brown silty fine to medium grained sand, dry, medium dense, slightly friable, slightly porous TERRACE DEPOSITS: Light red brown clayey fine to medium grained sand, damp, very dense, scattered roots to 1/2 Inch Total depth 3.5 feet No Water or cavina 10.0- 15.0- 0.0 TEST PIT NO. TP-2 ELEVATION: 119 6.8 SM SM 5.0— UNDOCUMENTED FILL: Light red brown silty fine to medium grained sand, dry, loose to medium dense, friable, organic debris, asphalt fragments to 4 inches in widest dimension @ 18": Dark red brown to orange brown clayey imedium to coarse grained sand, damp, modium dense, scatte.'-ed fine root hairs @ 20 to 26": abundant asphalt fragments TOPSOIL: Light gray brown silty fine to medium grained sand, dry, medium dense, slightly friable, slightlv porous ' Total depth 51 inches No caving or water 0.0- 5.0- LOG OF TEST PITS HETHERINGTON ENGINEERING, INC. GEOTECHNICAL CONSULTANTS 4237 Clearview Drive Carlsbad, California PROJECTNO. 4865.1 FIGURE NO. BACKHOE COMPANY: Mansolf Excavation BUCKET SIZE: Hand Pit 1 ^ 04 ta -0.0 -— 2 CQ EH H ^ W U-l >H 2 O ai fc3 & Q C DATE: 09/30/04 CO TUR — TUR z TUR fcj CO z — M o c * O u — CO Cfl CO SOIL DESCRIPTION TEST PIT NO.TP-3 ELEVATION: 5.0— 10.0— 95 ^ 84 83 10.5 10.5 SM; 13.5 SM UNDOCUMENTED FILL: Light red brown gravelly silty sand moist, loose to medium dense, abundant organic and metallic debris, caving 4-5 feet. TOPSOIL: Light gray brown silty fine to medium grained sand dry, medium dense, slightly friable, slightly porous ' Total depth 6 feet No water. Minor caving 4-5 feet in fill. 15.0- -0.0 5.0— TEST PIT NO.TP-4 ELEVATION: -1 SM TOPSOIL: Light gray brown Silty fine to medium grained sand 1 dry, medium dense, slightly friable, slightly porous ' -^mM 109 8.0 TERRACE DEPOSITS: Light red brown clayey fine to medium U grained sand, damp, very dense, scattered .-oots to 1/2 inch M i 1 1 i Total depth 3.5 feet M No Water or caving 10.0- 15.0- LOG OF TEST PITS HETHERINGTON ENGINEERING, INC. GEOTECHNICAL CONSULTANTS 4237 Clearview Drive Carlsbad, California PROJECTNO. 4865.1 ^FiGURENO. BACKHOE COMPANY: Mansolf Excavation BUCKET SIZE: Hand Pit DATE: 09/30/04 1 I ] I ] I 1 I ] 1 1 1 1 X E- Cu K H fc Q - •0.0 CO z m COIE E^: E c — CO CO CO < u u 1-3 CO M O D SM SOIL DESCRIPTION TEST PIT NO.TP-5 ELEVATION: UNDOCUMENTED FILL: Light red brown silty fine to medium grained sand, dry, loose to medium dense, friable, with dark black gray organic rich pockets SM 5.0- 10.0— 15.0- TOPSOIL: Light gray brown silty fine to medium grained sand, dry, medium dense, slightly friable, slightly porous Total depth 3 feet No Water or caving LOG OF TEST PITS HETHERINGTON ENGINEERING, GEOTECHNICAL CONSULTANTS INC. 4237 Clearview Drive Carisbad, California PROJECT NO. 4865.1 FIGURE NO. LABORATORY TEST RESULTS DIRECT SHEAR (ASTM: D 3080) Sample Location Angle of Internal Friction (°) Cohesion (psf) Remarks TP-1 @ 0-1' 30 150 Remolded in-place density and moisture, consolidated, saturated, drained SULFATE TEST RESULTS (EPA 9038) Sample Location Soluble Sulfate in Soil (%) TP-1 (OJ.O-V 0.0299 SUIVIMARY OF MAXIMUM DRY DENSITY/OPTIMUM MOISTURE CONTENT DETERMINATIONS (ASTM: D 1557-91A) Sample Description Maximum Dry Optimum Moisture Content Number Density (pcf) (%) 1 Red silt^/ sand, fine grained 126.0 10.0 2 Red silty sand, medium grained 130.0 9.0 Figure No. 6 ProjectNo. 4865.1 ' Log No. 8648