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Home My WebLink AboutCDP 2018-0002; MINICILLI RESIDENCE; LIMITED SOIL INVESTIGATION; 2009-04-20a ALLIED EARTH TECHNO L O G Y 9833 PACIFIC HEIGHTS BOUL E V A R D , SUITE C SAN DIEGO, CALIFORNIA 92121 PH. (858) 4574515 FAX (858) 457-4151 ROBERT CHAN, P.E. )1 LThflTED SOW INVESTIGATION / PROPOSED GRANNY FLAT SITE I-A 3926 IIIGIILANI) DRIVE CARLSBAD, CALIFORNIA FOR DIVERSIFIED CONSTRUCTION, INC. PROJECT NO. 09-1106G6 ALLIED EARTH TECHNOLOGY 9833 PACIFIC HEIGHTS BOULEVARD, SUITE C SAN DIEGO, CALIFORNIA 92121 PH. (858) 4574515 FAX (858) 4574151 ROBERT CHAN, P.E. April 20, 2009 Diversified Construction, Inc. 1745 E. Vista Way, #10 Vista, CA. 92084 Subject: Project No. 09-1106G6 Limited Soil Investigation Proposed Granny Flat Site 3926 Highland Drive Carlsbad, California Gentlemen In accordance with your request, we have performed a limited soil investigation for the proposed granny flat site on subject property, more specifically referred to as being APN 207-130-60-00, in the City of Carlsbad, State of California. It is our understanding that a granny flat building is proposed along the rear of the property. The proposed structure will be one-story in height; of woodframe/stucco and slab-on-grade construction. The approximate location of subject property is shown on Figure No. 1, entitled, "Site Location Map". The purpose of this limited soil investigation was to inspect and determine the subsurface soil conditions and certain physical engineering properties of the soils beneath the site, so that engineering recommendations could be presented for the safe and economical development of the site as proposed. In order to accomplish this purpose, representatives of our firm. visited the site on April 16, 2009, to review the topography and general site conditions. Two exploratory borings were excavated on the site. The approximate location of these exploratory borings are shown on Figure No. 2, entitled, "Approximate Location of Exploratory Borings". Project No. 09-1106G6 Diversified Construction, Inc. 04/20/09 Page 2 3926 Highland Drive The exploratory borings were excavated to depths varying from 3 to 4 feet below existing ground surface. The soils encountered in the exploratory borings were logged by our field representative, and the results summarized on Figure Nos. 3 and 4, each entitled, "Boring Log Sheet". The in-situ densities of the soils encountered were determined with a Triggs penetrometer. Samples of the soils encountered were obtained for laboratory testing and analysis, as presented on page L-1 attached hereto. 1. From the site inspection, it was determined that: Subject property is a rectangular-shaped lot of approximately 0.25 acres, situated on the east side of Highland Drive, approximately 125 feet south of the intersection with Tamarack Avenue. A single-story single-family residence currently occupies a level area along the front westerly portion of the site. Along the rear of the existing residence, there is a small backyard with a wood deck. Beyond the backyard, a fill slope on the order of 12 feet in height descends in an easterly direction. Beyond the toe of the fill slope, the existing ground slope gently in an easterly direction. From available public record, it is our understanding that the existing residence, consisting of 1,012 square feet, was constructed in 1944. C. The proposed granny flat will be situated along the toe of the existing fill slope. The soil types encountered at the proposed site consist of Quaternary age terrace deposits. As encountered in the exploratory borings, these soils consist of brown to reddish brown, medium dense to dense silty sands. No seepage was noted in the exploratory borings, and no watercourses will be interrupted by the proposed construction. Laboratory test results indicate that the soils encountered on the site possess low expansion potential (Expansion Index = 28). 2. Based on the results of the investigation, there appear to be no significant geotechnical hazard constraints on site that preclude the proposed development, and it is our opinion that the development is feasible from a geotechnical engineering standpoint, provided that the recommendations presented in this Project No. 09-1106G6 Diversified Construction, Inc. 04/20/09 Page 3 3926 Highland Drive report are incorporated into the design plan(s) and are properly implemented during the construction phase: It is recommended that a safe allowable soil bearing value of 2,000 pounds per square foot be used for the design and checking of continuous footings that are 12 inches in minimum horizontal dimension, and isolated pier footings that are 15 inches in minimum horizontal dimension, and are embedded at least 12 inches (for one story) and 18 inches (for two stories) below the surface of the competent natural or compacted fill soils. It is recommended that the continuous footings for the proposed structure be reinforced with a minimum of 4 #4 rebars; two rebars located near the top, and the other two rebars near the bottom of the footings. All isolated pier footings should be reinforced with a minimum of 2 #4 rebars in both directions, placed near the bottom of the footings. The concrete slab-on-grade should be 4 inches in thickness, and be reinforced with #3 rebars @ 18 inches on center in both directions, placed at mid-height of concrete slab. The concrete slab should be underlain by 4 inches of clean sand and a 10-mil moisture barrier in moisture sensitive areas. The above foundation and slab reinforcement requirements are based on soil characteristics, and should be superceded by the requirements of the project architect. d. It is our understanding that a retaining wall may be constructed westerly of the proposed granny flat. It is recommended that retaining walls be designed to withstand the pressure exerted by equivalent fluid weights given below: Equivalent Backfill Fluid Surface Pressure (horizontal : vertical) (pet) Level 35 2:1 52 1%:! 58 Project No. 09-1106G6 Diversified Construction, Inc. 04/20/09 Page 4 3926 Highland Drive The above values assume that the retaining walls are unrestrained from movement, and have a granular backfill. For retaining walls restrained from movement at the top, such as basement retaining walls, an uniform horizontal pressure of 7H (where H is the height of the retaining wall in feet) should be applied in addition to the active pressure recommended above. All retaining walls should be supplied with a backfill drainage system adequate to prevent the buildup of hydrostatic pressure. The subdrain should consist of one-inch gravel and a perforated pipe near the bottom of the retaining wall. The width of this subdrain should be at least 12 inches, and extend at least 2/3 the height of the retaining wall. The subdrain should be enclosed in a geotextile fabric. All backfill soils behind the retaining wall should be compacted to at least 90 percent of maximum thy density in accordance with ASTM D1557. To resist lateral loads, it is recommended that the pressure exerted by an equivalent fluid weight of 275 pounds per square foot per foot of depth (maximum of 1,200 pounds per square foot) be used for footings or shear keys poured neat against competent natural or compacted fill soils. The upper 12 inches of material in areas not protected by floor slabs or pavements should not be included in the design for passive resistance. This value assumes that the horizontal distance of the soil mass extends at least 10 feet or three times the height of the surface generating the passive pressure, whichever is greater. A coefficient of sliding friction of 0.35 (total frictional resistance equals coefficients of friction times the dead load) may be used for cast-in-place concrete on competent natural or compacted fill soils. Footings can be designed to resist lateral loads by using a combination of sliding friction and passive resistance. The coefficient of friction should be applied to dead load forces only. Seismic earth pressures can be taken as an inverted triangular distribution with a maximum pressure at the top equal to 12H pound per square foot (with H being the height of retained earth in feet). This pressure is in addition to the static design wall load. The allowable passive pressure and bearing capacity can be increased by 1/3 in determining the stability of the wall. A factor-of-safety of 1.2 can be used in determining the stability of the retaining wall under seismic conditions. I Project No. 09-1106(36 Diversified Construction, Inc. 04/20/09 Page 5 3926 Highland Drive It is recommended that all footings placed on the fill slope be setback such that the bottom of the footing at the outer edge is at least 7 feet back from the face of slope at that level. For footings of structures subject to lateral forces, such as those of a retaining wall, the above setback should be increased to 10 feet. The seismic coefficients in accordance with the current California Building Code were determined and the results are presented below: Site Coordinates: Latitude = 33.15455 Longitude = -117.32992 Site Class = D Site Coefficient Fa = 1.00 Site Coefficient Fv = 1.521 Spectral Response Acceleration At Short Periods Ss = 1.271 Spectral Response Acceleration At 1-second Period Si = 0.479 Sms = FaSs 1.271 Smi = FvS1 = 0.728 Sds = 2/3*Sms = 0.848 Sd1 = 2/3*Sm1 = 0.486 1. In consideration of the competent natural soils underlying the site, and the lack of a permanent groundwater table near the ground surface, it is our opinion that soil liquefaction does not present a significant geotechnical hazard to the proposed site development M. It is recommended that our finn inspect the foundation trench excavations to ensure proper embedment in competent natural soils. It is recommended that our firm review the foundation plans to ascertain that the recommendations presented herein are incorporated. It is further recommended that the proposed addition be constructed in accordance with the approved plans and applicable regulations, except where items 2(a) to (n) above are more stringent. /.•' ------r V Y I S Project No. 09-1106G6 Page L-1, anre Respetfti1Iç subn3id, ,JAtD EARTJ7(TEC kOBERT CHNI. Diversified Construction, Inc. 04/20/09 Page 6 3926 Highland Drive 1 to 4, inclusive, are parts of this report. Project No. 09-1106G6 Diversified Construction, Inc. 04/20/09 Page L-1 3926 Highland Drive LABORATORY TEST RESULTS The maximum dry density and optimum moisture content of the fill soils encountered were determined in accordance with A.S.T.M. D1557, Method A. The results of the tests are presented as follows: Soil Soil Dry Density Moisture Content Type Description (lbs./cu.ft) (% Dry Wt.) I Brown silty fine to medium sand 124.5 10.5 (SM) The Expansion Index of the most clayey soils was determined in accordance with UBC Test No. 18-2. The results of the test are presented as follows: Soil Soil Expansion Type Description Index 1. Brown silty fine to medium sand (SM) 28* *Considered to possess low expansion potential jaMb oF . Cameo Rd ' Y Ale L vi- It ' \. mpp .7 A/ - . S Point P1 ...; --'•. A7 4. Havens \ .5 • VCIO AN CD :S 40 çdç•' . .: . s ç 5 'S I3IPdtlC V ( S S ca P Id 5- 5 st ' C2O9P.upO.iv.IIr.c - - .MapDtz+2OO9NAVTIO or Te1eAts, I NOT TO SCALE PROJECT NO. 09-1106 G6 FIGURE NO.1 I ! EXISTING 40 HOUSE 401 W-V ai. - - I - &I N 887 APPROXIMATE LOCATION OF EXPLORATORY BORING5 i. 1' • \\ 41241 8#2 /1 7 •. - 150A2 ( .,. 888 LEGEND SCALE 1"=20' APPROXIMATE LOCATION OF EXPLORATORY BORING PROJECT NO. 09-1106 G6 FIGURE NO.2 BORING LOG SHEET UIIJi1J[eE(II FT. DESCRIPTION SOIL TYPE - 0 Brown, damp, slightly dense SILTY SAND (SM) • (topsoils) • 1 Brown, moist, medium dense 12*"SILTY SAND (SM) (Quaternary terrace deposits) 2 23* 3 28* Bottom of Boring (No refusal) LEGEND 0 - Indicates representative sample - Indicates blowcount/10 cm/Triggs penetrometer Granular Cohesive 0 Very loose 0 Very soft 5 Loose 2 Soft 11 Medium dense 5 Medium stiff 31 Dense 9 Stiff 51 Very dense 16 Very stiff 31 Hard Project No. 09-1106G6 Figure No. 3 BORING LOG SKEET BORING NO.2 FT. DESCRIPTION SOIL TYPE - - 0 Light brown, damp, loose SILTY SANDS (SM) (topsoils) 1 Brown, moist, medium dense 15* SILTY SANDS (SM) dense • 2 (Quaternary Terrace Deposits) 25* 3 dense 3* 4 Some cobbles to 3" dia. 39* Bottom of Boring (No refusal) Project No. 09-1106G6 Figure No. 4