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Home My WebLink AboutCT 08-06; HIGHLAND JAMES; SITE INSPECTION; 2005-09-02• I alp SOMA TRNTh4j P.O. Box 1195 September 2, 2005 Lakeside, California 92040 (619) 443-0060 Mike O'Gara P.O. Box 1633 Carlsbad, California 92018 Subject: He No. 1106F3-05 SITE INSPECHON Proposed Residential Building Site 3980 Highland Avenue City of Carlsbad Dear Mr. O'Gara: SCOPE In accordance with your request, a Site Inspection has been performed at the subject site. The purpose of this investigation was to examine existing site conditions and provide engineering recommendations for the live, proposed two-stoly over basement, single-family residential Structures. FIELD INSPECHON In order to accomplish this purpose, a representative of this firm visited the site, reviewed the topography and site conditions and visually and textually classified the surface and near surface soils. Representative samples of the on-site soils were obtained from three test explorations approximately four to fifteen feet in depth and tested for density, shear strength and expansive characteristics. SITE CONDITIONS The subject site is a residential parcel located on the easterly side of Highland Drive. The property is located at the top of a rise with the east side of the property fronting James Drive approximately 15 to 20 feet lower than the west side. A 10-foot, 2:1 cut slope extends midway through the site from the south to north. A 2 to 3 feet fill slope is located at the top of the cut on the north end. The property is presently occupied by a one-story single-family residence with detached garage. There is a four-foot retaining wall behind the garage and a 3-foot rock retaining wall behind the house. Adjacent properties are occupied by residential structures. Mike O'Gara File No. 1106173-05 September 2, 2005 Man-made fill soils were encountered to a depth of approximately one to three feet during the course of this inspection; however, native soils were loose and compressible to approximately 15 feet in depth. SOTh CONDITIONS Soils encountered in Test Exploration No. 3 at the higher elevation off Highland Drive were generally firm to medium dense, cemented, red brown silty sands becoming more dense with depth to the bottom of the excavation, approximately four feet in depth Test Explorations Nos. I and 2 were located below the cut at the lower elevation off James Drive. Soils encountered in these explorations were generally loose to firm granular sands to 10 to 15 feet in depth. Dense formational soils were not encountered at the lower elevation. None of the soils we encountered were considered to be detrimentally expansive with respect to change in volume with change in moisture content. CONCLUSIONS AND RECOMMENDATIONS The loose native soils we encountered at the lower elevations should not be utilized to support the proposed new structures. In order to provide adequate support, the loose soils should be removed to at least five feet below the lowest footing and the bottom of the excavation compacted using a vibratory compacter. The bottom of the excavation should be tested to insure that compaction is at least 90 percent of maximum dry density. The soils may then be replaced and recompacted to at least 90 percent of maximum dry density in accordance with the Grading Specifications in this report. The recompaction should extend at least 5 feet outside the proposed building footprint. Any deleterious material that may be encountered should be removed prior to recompaction. We anticipate that basement excavations for the structures located in the higher elevations will achieve suitable soils for adequate support. The basement excavations should be inspected by a representative of this firm to insure that proper soil strata have been achieved. No special foundation design to resist expansive soil is necessary. Conventional spread footings founded a minimum of 12 inches below lowest adjacent grade and having a width determined by the allowable soil bearing value as detailed above may be used for foundation support. Footing widths should be at least 12 inches for continuous footings and 24 inches for square footings due to practical considerations as well as Building Code requirements. These recommendations are based upon the soil type only and do not take into consideration structural requirements. OQ S . Mike O'Gara File No. 1106173-05 September 2, 2005 Reinforcing in footings should consist of at least one #4 steel bar placed continuously in the top and bottom of continuous footings regardless of structural requirements. Reinforcing for isolated footings are dictated by the structural requirements. These recommendations are based upon the soil type encountered and do not take into consideration the proposed bearing load. Concrete slabs-on-grade should be constructed to have a nominal thickness of 4" and underlain with a sand blanket of 3 inches in thickness. Provide minimum temperature reinforcement consisting of 6X6-10/10 welded wire mesh. The sand subbase (sand blanket) should have a sand equivalent exceeding 30 per ASTM D2419. All slabs should either have a conventional thickened edge or be poured monolithically with continuous footings at the slabs perimeter. Conventional thickened edges should be 8" thick at slab edge, uniformly tapering to 4" thick at 2' from slab edge. The thickened edges or monolithic footings should extend completely around the slab's perimeter. Construction and expansion joints should be considered slab edges. Maximum spacing of expansion joints is 50' for interior slabs and 30' for exterior slabs. A representative sample of the foundation soil was remolded to 900/,D of maximum dry density. Based on the following test results, a safe allowable bearing value of at least 2500 pounds per square foot for 12 inch deep footings may be used in designing the foundations and slab for the proposed structures. This value may be increased by one third for wind and/or seismic loading. Soil Description Red brown silty sand Depth of Sample 3' Angle of internal friction 390 Cohesion 243 psf Unit weight 121.0 pcf Maximum Dry Density 133.4 pd Optimum Moisture Content 8.5% Expansion Index 31 Resistance to horizontal movement may be provided by allowable soil passive pressure and/or coefficient of friction of concrete to soil. The allowable passive pressure may be assumed to be 500 psf at the surface and increasing at the rate of 500 psf per foot of depth. These pressures assume a frictionless vertical element, no surcharge and level adjacent grade. If these assumptions are incorrect, we should be contacted for values that reflect the true conditions. The values are for static conditions and may be increased 1/3 for wind and/or seismic loading. The coefficient of friction of concrete to soil may be safely assumed to be 0.5. 3 . I Mike O'Gara File No. 1106F3-05 September 2, 2005 8. Active pressures for the design of unrestrained, cantilevered, individually supported retaining walls capable of slight movement away from load may be considered to be equivalent to the pressures developed by a fluid with a density of 30 pcf. This value assumes a vertical, smooth wall and level drained backfill. We should be contacted for new pressures if these assumptions are incorrect. Restrained walls, incapable of movement away from load without damage such as basement walls, should be designed for the additional equivalent fluid of 24 pcf applied triangularly for cohesionless type soils and trapezoidally for cohesive type soils. The above design values and foundation design assume that the basement wall excavations will expose soils similar to those we tested during our site inspection. We should inspect the cut to insure that the soils exposed are the same as those we tested. For any grading proposed or contemplated for this project, the following grading specifications should be utilized. RECOMMENDED GRADING SPECIFICATIONS Proposed Residential Building Site 3980 Highland Avenue City of Carlsbad GENERAL: Soil Testers and 'Soil Engineer' are synonymous hereinafter and shall be employed to inspect and test earthwork in accordance with these specifications, the accepted plans, and the requirements of any jurisdictive governmental agencies. They are to be allowed adequate access so that the inspections and tests may be performed. The Soil Engineer shall be apprised of schedules and any unforeseen soil conditions. Substandard conditions or workmanship, inadequate compaction, adverse weather, or deviation from the lines and grades shown on the plans, etc., shall be cause for the soil engineer to either stop construction until the conditions are corrected or recommend rejection of the work. Refusal to comply with these specifications or the recommendations and/or interpretations of the soil engineer will be cause for the soil engineer and/or his representative to immediately terminate his services. Deviations from the recommendations of the Soil Report, from the plans, or from these Specifications must be approved in writing by the owner and the contractor and endorsed by the soil engineer. 4 S S Mike O'Gara FileNo. 1106F3-05 September 2, 2005 SOIL TEST METHODS: Maximum Density & Opt Moisture Density of Soil In-Place Soil Expansion Shear Strength Gradation & Grain Size Capillary Moisture Tension Organic Content - ASTM D1557-70 -- ASTM Di 556, D2922 and D3017 - UBC STANDARD 29-2 -- ASTM D3080-72 -- ASTM D1140-71 -- ASTM D2325-68 - % Weight loss after heating for 24 hours at 300° F and after deducting soil moisture. LIMITING SOIL CONDITIONS: Minimum Compaction 901/6 for 'disturbed' soils. (Existing fill, newly placed fill, plowed ground, etc.) 84% for natural, undisturbed soils. 95% for pavement subgrade within 2 of finish grade and pavement base course. Expansive Soils Expansion index exceeding 20 Insufficient fines Less than 40% passing the #4 sieve. Oversized Particles Rocks over io" in diameter. PREPARATION OF AREAS TO RECEIVE FILL: Brush, trash, debris and detrimental soils shall be cleared from the areas to receive 1111. Detrimental soils shall be removed to firm competent soil. Slopes exceeding 20% should be stepped uphill with benches 10' or greater in width- Scarify area to receive fill to 6" depth and compact. FILL MATERIAL shall not contain insufficient fines, oversized particles, or excessive organics. On-site disposition of oversized rock or expansive soils is to be at the written direction of the Soil Engineer. Select fill shall be as specified by the soil engineer. All fills shall h ('nmpacteA1 and tested. SJJBDRAINS shall be installed if required by and as directed by and detailed by the soil engineer and shall be left operable and unobstructed. They shall consist of 3" plastic perforated pipe set in a minimum cover of 4" of filter rock in a 'vee' ditch to intercept and drain free ground from the mass fills. Perforated pipe shall be schedule 40, Poly-Vinyl-Chloride or Acrylonitrile Butadienne Styrene plastic. Rock filter material shall conform to the following gradation: Sieve size: 3/4" #4 930 #200 %Passing: 90-100 25-50 5-20 0-7 5 [] Mike O'Gara File No. 1106F3-05 September 2, 2005 Subdrains shall be set at a minimum gradient of 0.2% to drain by gravity and shall be tested by dye flushing before acceptance. Drains found inoperable shall be excavated and replaced. CAPPING EXPANSIVE SOILS: If capping expansive soils with non-expansive soil to mitigate the expansive potential is used, the cap should be compacted, non-expansive, select soil placed for a minimum thickness 3' over the expansive soil and for a minimum distance of 8' beyond the exterior perimeter of the structure. Special precautions should be taken to ensure that the non-expansive soil remains uncontaminated and the minimum thickness and dimensions around the structure are maintained. The expansive soils underlying the cap of non-expansive cap should be pre-saturated to a depth of 3' to obtain a degree saturation exceeding 90% before any construction supported by the compacted cap. The non-expansive soil comprising the cap should conform to the following: Minimum Compaction 90% Maximum Expansion Index 30 Minimum Angle of Internal Friction 33 Deg Cohesion Intercept 100 psf UNFORESEEN CONDH1ONS: Soil Testers assume no responsibility for conditions, which differ from those, described in the applicable current reports and documents for this property. Upon termination of the soil engineer's services for any reason, his fees up to the time of termination become due and payable. If it is necessary for the soil engineer to issue an unfavorable report concerning the work that he has been hired to test and inspect, the soil engineer shall not be held liable for any damages that might result from his 'unfavorable report'. If we can be of any fi.trther assistance, please do not hesitate to contact our office. This opportunity to be of service is sincerely appreciated. Respectfully submitted, C. NO. 21,650 Cr1 EXR9/30109 A11 A 13 A EXPLORATION TRENCH -',VO $iir - LOCATION OF EXPLORATION TRENCHES I %ftIL 11421 Woodside Ave., Suite C Santee, California 92071 (619) 562-0500 S Mike O'Gara File No. 1106F3-05 September 2, 2005 Plate No. 2 EXPLORATION NUMBER 1 Date Logged: 6/28/05 Date Reported: 9/02/05 Depth Unified Classifications Equipment Used: Groundwater: Refusal: Soil Description Backhoe Not Encountered Not Encountered Soil Type 0 to 6' SM Red brown, humid, loose, SILTY SAND with clay binder (Native) 1 6 to 15' SM Red brown, humid, firm, SILTY SAND with clay binder (Native) Darker brown, _wet, _firm, _SILTY _SAND 1 Limit of Equipment . Mike O'Gara File No. 1106F3-05 September 2, 2005 Plate No. 3 EXPLORATION NUMBER 2 Date Logged: 6/28/05 Equipment Used: Backhoe Date Reported: 9/02105 Groundwater: Not Encountered Refusal: Not Encountered Depth Unified Classifications Soil Description Soil Type 0 to 10' SM Red brown, moist, firm to medium dense, cemented, SILTY SAND (Native) I 10 to 11' SM Tan moist, loose, cemented, granular, SILTY SAND (Native) Bottom of trench _____ 11 S Mike O'Gara File No. 1106F3-05 September 2, 2005 Plate No. 4 EXPLORATION NUMBER 3 Date Logged: 6/28/05 Date Reported: 9/02/05 Depth Unified Classifications Equipment Used: Groundwater,: Refusal: Soil Description Backhoe Not Encountered Not Encountered Soil Type 0 to 41 SM Red brown, humid, medium dense, SILTY SAND (Native) bottom of trench SOIL TEST RESULTS ON REMOLDED SAMPLES REMOLDED SPECIMENS Soil Type lassification Sample Tested General Description V V I V V Id Clsf v Color Texture I SM T13 Redbrown SILTYSAND Maximum Density (pct) Density (pct) Optimum Moisturel I Compaction Friction (deg) SpecWtcGravity Moisture Cohesion (psf) I Expansion Inde4 I Saturation V V V V V V V V V V Ymx OMc Gs El Yd Rc we Ds Fr c 133.4 8.5 2.65 20 121.4 91% 6.4% 75% 39 243