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HomeMy WebLinkAboutPD 2019-0023; LIN RESIDENCE; SOIL REPORT FOR PREPOSED BUILDING CONSTRUCTION ON 2736 ARLAND ROAD; 2019-06-20SOIL REPORT FOR PEOPOSED BUILDING CONSTRUCTION ON 2736 ARLAND ROAD CARLSBAD, CALIFORNIA PREPARED FOR MICHELLE LIN 2736 ARLAND ROAD CALRSBAD, CA 92008 PREPARED BY S.H. SHU, GE 4025 HARBOR DRIVE CARLSBAD, CALIFORNIA 92008 --_ /401101019 RECE IVED JUL 10 2019 LAND DEVELOPMENT ENGINEERING SOIL REPORT FOR 2736 ARLAND ROAD CARLSBAD, CALIFORNIA I. INTRODUCTION This report presents the results of a geotechnical evaluation of the site located at 2736 Arland road, Carlsbad, California. The site is legally known as Parcel A, Parcel Map No. 20908, in the City of Carlsbad. County of San Diego, State of California, recorded on 18th day of August, 2011 in the office of County Recorder of San Diego County, State of California, (APN- 156-142-56). The general location of the site is shown on Figure 1. The purpose of this study was to provide geotechnical input to the appropriate governmental authorities that control the issuance of necessary permits or approval of the planned subdivision. The geotechnical evaluation was based on the followings: Observation of existing site conditions. Observation of the exposed soil conditions in two of the test pits explored within the proposed new lot. Logging, sampling and test of representative soil samples from the pits. Review of published geological and soil conditions data at or near the site, and Preparation of this report presenting my findings, conclusions and recommendations. II. SITE DESCRIPTION AND PROPOSED SUBDIVISION The proposed building lot (Parcel C) is located immediately east of the existing two-story building at 2732 and 2734 Arland Road, in the City of Carlsbad, California. Access to the site is via Arland Road to the wçst. The proposed construction site Parcel (C) is approximately 20,528 sf with an RI -7500 zoning. The new lot (C) created will be approximately 156.75 foot deep and 125.73 foot wide (See figure 1). III. FIELD EXPLORATION & LABORATORY SOIL TESTING Two test pits (see Figure 1) were explored manually within the planned two building sites (Parcel Q. The test pits were excavated to depths ranging from 18 to 30 inches below existing ground surface where hard formatioal soils have prevented excavation below these depths. The soil layers encountered are described below: Test Pit 1: 0-12": Top soils, silty fine to medium sand, dry to moderately moist with some wet spots, brown to dark brown in color, moderately compact with some loosely cultivated loose spots. 12-18": Formational materials, also silty fine to medium sand, but compact, moist, reddish brown to brown. End of excavation at 18". Test Pit 2: 0-12": Top soils, same as Pit 1, dark brown, graded into brown with depth, some root lets, organic, slightly moist to moist, loose. 12-30": Formational materials, reddish brown to brown silty fine to medium sand, compact. End of excavation at 30". Based on the results of field excavations and the research of the published geological and soil literatures, the subject site is covered with shallow top soils (slope wash material) to a depth of approximately 12 inches below existing ground surface. The top soil layer is underlain by firm formational materials consisting essentially of reddish brown to brown silty fine to medium sand to the end of exactions. Because of uniformity in soil profile, the excavation was terminated at relatively shallow depth. Physical properties, such as maximum dry density compressibility and expansiveness of both on-site top soils and remolded compacted soils, were previously tested reported by the writer in Reference 1. Geologically, both top soils and the formational materials are known locally as Pleistocene-aged marine terrace deposit. The US Department of Agriculture has classified and grouped the deposit into Marina loamy sand, 2 to 9 percent slope series with a description symbol of MIC. (See Reference: "Soil Survey" By USDA Soil Conservation and Forest Service in cooperation with UC Agricultural Experiment Station, US Department of the Interior, Bureau of Indian Affairs, Department of the Navy, and the USA Marine Corps, 1973). This series of soil spreads widely along the coastal area of North San Diego area. The MIC series of deposit consists essentially of somewhat excessively drained soils derived from weakly consolidated to non-coherent ferruginous loamy sand. The representative profile of the surface layer is brown and dark yellowish brown, medium acid to slightly acidic loamy sand about lO-inchin thickness. The subsoil is brown and neutral to mild alkaline loamy sand deposit of approximately 47 inches in thickness. It is uniformly non-expansive, non-sticky with non-to low plasticity. The deposit is permeable and erosive. The available water holding capacity is approximately 4 to 5 inches. The average particle size of MIC series is 2.0 to 0.005 millimeter and it typically has less than 35 percent of fine particles passing US 200 standard sieve sizes (74 microns or 0.0029 inch). Note Reference 1: "Soil Report for Prosed Building Construction on 2732 Arland Rd. Ca 92008, MS 08-06, prepared for Michelle Lin, 2732 Arland Rd. Carlsbad, Ca. Dated on: 08/08/2013 IV. SEISMIC GEOLOGIC SETTINGS The western San Diego region has historically been an area of low seismic activities (Allen et all, 1969, page - - 753). All of San Diego county, the northwestern tip of Baja California and much of the peripheral offshore areas have been devoid of large earthquake epicenters since 1932. Smaller earthquakes with a magnitude (Richter scale) of 3.9 or less have occurred within this area, but they have been scattered both spatially and temporarily. On the whole, very little damage, if any, occurred as the results of these small earthquakes. The largest recent earthquakes were the low-magnitude of 3.7 and 3.6 events on June 21 and 22, 1964 with epicenters near southeast San Diego. Both of the local events had the maximum Modified Mercalli intensities of VI and caused only slight damage. In San Diego region, future earthquakes are most likely to associate with the prominent local faults, such as Rose Canyon fault, the La Nacion fault or the Sweetwater fault. Among these, the Rose canyon fault is the closest to the job site and would probably govern the selection of the required earthquake design criteria for the proposed project. However, this fault is still considered to be only 3 "potentially active to low potential" category fault rather than an "active" fault. Elliot has studied this fault, and concluded that the Rose Canyon fault might produce an earthquake having a magnitude of 4.8 in a 100 years recurrence time. In the absence of known active fault in the vicinity of the site as well as within the Aiquist-Priolo Earthquake Fault Zone, the most likely place for these damaging earthquakes to occur in future is along the known active faults that lie within the Southern California region outside San Diego area. This is because most of the large earthquakes in California are related to movements along active faults that lie within the Southern California region outside San Diego area. This is because most of the large earthquakes in California are related to movements along active faults. The closest active fault known to exist outside San Diego area is the Newport- Inglewood fault located approximately 5.6 miles west of the site. Earthquake design of future building at the new subdivision lot may be based on the design parameters listed on the 2016 California Building Code ASCE 7-10 standard that are selected from this geologic setting. The specific earthquake design parameters recommended are presented in the RECOMMENDATIONS section of this report. In addition, liquefaction potential on the site during earthquake shaking is nil due to dense nature of the formational materials and the absence of ground water body nearby. IV. CONCLUSIONS Based on the results of field investigations and study, it is the writer's opinion that the existing site is feasible for subdividing to facilitate new construction as long as the subdivision conforms to the local zoning ordinance. There will be no geologic or soil constraints that would prevent the new subdivision lot from new construction. The integrity of the existing owner's building at the site is exemplary to the favorable geology and soil conditions. In addition, the subject is neither in the vicinity of a lake or a natural water body nor in amidst of a natural water course. The subsurface materials consist mainly of firm formational deposit. Therefore, the site should be devoid of soil liquefaction during earthquake shaking. RECOMMENDATIONS Foundation Design and Construction: Conventional spread footing and continuous perimeter footing may be used to support future building at new subdivided lot. The footings may either by founded on the firm native formational soils or on the compacted fill. The required minimum depth for footings on both formational and compacted fill is 12 inches below the compacted or undistrubed fill. Insert (C), the presence or absence of gopher holes or lateral force design requirement may govern the required footing depth. The recommended minimum width for continuous footing is -1-2 inches; and-l8 inches 'for square footing. Insert (C): All footings should also be located at least 5 feet horizontally from the top adjacent slope. All footings so designed and placed at the recommended minimum depth may be loaded to a maximum unit foundation pressure of 2500 pounds per square foot. This value is for dead and live loads only. It may be increased one third for combined dead, live and transient seismic or wind load. 4 After footing trench excavations, the exposed soils in the trench should be observed by a Geotechnical Engineer before pouring concrete. If loose soil is detrimental organic or debris is exposed, the footing depth may be deepened or these should be removed. Insert (D) properly compacted to at least 90 percent of the maximum dry density. Where unexpected gopher tunnel is encountered, the tunnel should be grouted or be removed for compaction. - - - Insert (D): The removed materials can be replaced with compacted fills. Lateral Resistance Design: The lateral force may be resisted by the combination of (a) the friction developed between the footings and the bearing soils and (b) the passive pressure developed on the side faces of the footings. To estimate frictional resistance component, a frictional coefficient of 0.4 may be used. To estimate passive resistance of the soil on the side of footing, 300 pounds per square foot of depth is recommended for those footings completely surrounded and confined by a level ground. The recommended maximum passive pressure is 3000 pounds per square foot for the combined total of dead, live and seismic loads. Earthquake Resistant Design --Thernost-likeiy-place-for-potentially damaging earthquakes to occur in the future is along the known active Newport-Inglewood Fault located approximately 5.6 miles west of the site in the Southern California region. Based on these findings, the recommended seismic design parameters that may be used for earthquake design, per 2016 California Building Code ASCE 7-10 standard, is as follows: Seismic Design Parameters Site Location Latitude 33.169760 Longitude 117.339350 W Site Class D Maximum Spectral Response Acceleration Ss 1.131g Si 0.434g Adjusted Maximum Acceleration Srns 1.1 85g SMI 0.680g Design Spectral _Response Acceleration Parameters SDS 0.790g SDI 0.453g Concrete Slab on Grade: Both compacted fill or on site formational sub-grade soils can be considered non-expansive. Slab reinforcement, per local building ordinance, can be used. The suggested minimum slab reinforcement is one later of 6x6-l0xlO welded wire fabrics at the middle height of the slab. The slabs to be covered with flooring should be protected by an acceptable vapor barrier, such as 10 mil thick plastic sheet. To prevent punctures and aid in concrete cure, slab should be covered above with and underlain by clean sand later at least 4 inches in thickness. The sand later can serve to equalize intruded moisture and support a moisture vapor barrier sandwiched in the sand layer. Site Drainage: As onsite soils are erosive, it is necessary to confine both footing and slab bearing soils at all times. To accomplish this, an efficient site drainage system should be installed to drain away or to minimize surface run- off from adversely influencing the bearing soils. The efficient site drainage system should be maintained and all footings should also be kept at least 5-foot horizontally from the top of adjacent slopes at all times. Construction Observation and Testing: The conclusions and recommendations presented in this report are based on the information obtained from field explorations, laboratory testing of soils as well as research of available geo-technical publications pertinent to the site. As subsurface materials may vary from place to place, it is prudent to have exposed soils checked from time to time during construction and grading. The suggested phases of soil observation by a Geo-technical Engineer during grading and construction are listed below: After removal of top soils and before placing excavated soils for compaction. After foundation trench excavation before setting steels and pouring concrete. Before and after backfilling of utility trench, is any. Testing of compacted fill after placement. Temporary excavations in the vicinity of any existing structure, if any. If you have any questions regarding the information presented in this report, please feel free to call. Respectfully submitted. c;. S.H. Shu, CE 19913, GE 772, Date