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HomeMy WebLinkAboutCDP 2021-0048; WEINZETTLE-DIETRICH ADU; SOILS TECHNICAL STUDY; 2021-11-22November 22, 2021 Ben Leland Leland Construction 1421 W Lewis Street San Diego, California 92103 SUBJECT: Dear Mr. Leland: SCOPE File No. 1106E4-2I SITE INSPECTION Proposed Residential Building Site 2644 Jefferson Street City of Carlsbad P.O. Box 1195 Lakeside, California 92040 (619) 443-0060 RECEIVf:.tJ DEC 08 202! CITY or C ,\' :). '' l;\[_) PLANNING sl1VISION 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 proposed accessory dwelling unit. If project details vary significantly from those described, Soil Testers should be notified prior to final submittal for revision and possible revision of the recommendations presented herein This report is issued with the understanding that it is the responsibility of the owner or the owner's representative to ensure that the information and recommendations contained herein are brought to the attention of the architect and engineer for the project and incorporated into the plans, and the necessary steps are taken to see that the contractor and subcontractors carry out such recommendations in the field. FIELD INSPECTION In order to accomplish this purpose, a representative of this firm visited the site, reviewed the toJX)graphy and site conditions and visually and textually classified the surface and near surface soils. Representative samples of the on-site soils were obtained from a test 1 Leland Construction File No. l 106E4-21 November 22, 2021 exploration approximately 4 feet in depth and tested for density, shear strength and expansive characteristics. SITE CONDITIONS The subject site is located on the east side of Jefferson Street The site is a relatively level narrow lot with a split level single family residence. Neighboring properties are occupied by single and multi-family residential structures. Fill materials were encountered to a depth of approximately 14 inches during the course of this inspection. SOIL CONDITIONS Soils encountered in the test explorations were fill soils consisting of firm, brown to light brovm, dry, fine to medium, silty sands to approximately 14 inches in depth. These surface soils were underlain with native soils consisting of dense, orange-brown, dty, fine to coarse silty sands to the bottom of the trench approximately 4 feet in depth. Ground water was not encountered in the test pit The soils we encountered were not considered to be detrimentally expansive with respect to change in volume with change in moisture content. CONCLUSIONS AND RECOMMENDATIONS 1. A representative sample of the foundation soil was remolded to 90% of maximum dry density. Based on the following test results, a safe allowable bearing value of at least 2000 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. This value may be increased by 20 percent for each additional foot of depth and or width to a maximum of 3 times the designated value. Maximum Dry Density Optimum Moisture Angle of internal friction Cohesion Unit weight Expansion Index 130.1 pcf 9.2% 32° 194 psf 118.2 pcf 21 2. Lateral resistance to horizontal movement may be provided by the soil passive pressure and friction of concrete to soil. An allowable passive pressure of 250 2 Leland Construction File No. l l06E4-2l November 22, 2021 pounds per square foot per foot of depth may be used. A coefficient of friction of 0.35 is recommended. The soils passive pressure may be increased by 1/3 for wind and seismic loading. 3. The seismic parameters for the site coordinates 33.1662123°N, 117.348128°W for assumed Site Class Dare as follows: • Ss ~ 1.066 g • s, ~ 0.386 g Sms = 1.279g Sm1 = null s,, ~ 0.853 g Sd1 = null 4. Footings for the proposed structure must extend through any fill soils a minimum of 12 inches into competent fill soils. Anticipated footing depth is approximately 24 to 30 inches. Footing excavations should be inspected by a representative of this firm prior to placement of forms and reinforcing steel to ensure proper depth has been achieved and that all footings are founded a minimum of 12 inches into firm natural ground. Loose soils should be removed from excavations prior to our inspection. Tbis foundation depth is based upon the soil values only and does not take into consideration the structural requirements. The slab preparation in #8 must be adhered to for proposed slab construction. 5. The property to the east was observed to have large mature trees adjacent to the property line. The proposed accessory dwelling unit is setback 5 feet from the east property line. Although roots were not observed in our test pit, they may be encountered in the footing excavations and under the slab area Roots and organic material must be removed from the building foundation. It is suggested for the client to contact an arborist to assure that the trees are not damaged during the construction process. 6. 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 are recommended 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 entirely upon the soil types and do not take into consideration the requirements of the proposed structure. 7. 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 is dictated by the structural requirements. These recommendations are based upon on the soil type encountered and do not take into consideration the proposed bearing load. 3 Leland Construction File No. 1106E4-21 November 22, 2021 8. Concrete Slab-On-Grade, SOG, should be designed by the project's structural engineer based on anticipated loading conditions. We recommend that conventional reinforced concrete SOG for this project be founded on 4 inches of Class II Virgin Aggregate Base (with approximately 2% +/-over optimum moisture content and 90% compaction, relative to the lab maximum dry density, ASTM D 1557), overlying a 12 inch thick zone of adequately placed and compacted structural fill. A representative of our firm should be contacted during this process to approve the excavation and test the compaction. We recommend that a moisture barrier be provided by a membrane, visqueen IO mils in minimum thickness or equivalent, be placed at top of well compacted Class II Aggregate Base, then covered with 2 inches of moist clean sand having a minimum sand equivalent of 30 when tested in accordance with the American Society of Testing and Materials test method • ASTM D 1555. Floor slabs, as a minimum, should be 5 inches thick with #4 reinforcing steel at 16" on-center each way. Reinforcement should be placed at mid-height of the slab. The final slab thickness and reinforcement should be determined by the structural design engineer. Control joints should be provided in accordance with the recommendations of the structural design engineer. SITE EROSION CONTROL During the construction, surface water should be controlled via berms, gravel bags and1or sandbags, silt fence, straw wattles, siltation basins, while maintaining positive surface grades or other methods to avoid damage to the finish work or adjoining properties. All site entrances and exits must have coarse gravel or steel shaker plates to minimize offsite sediment tracking. Best management Practices (BMP's) must be used to protect storm drains and minimize pollution. The contractor should take measures to prevent erosion of graded areas until such time as permanent drainage and erosion control measures have been installed. After completion of grading, all excavated surfaces should exhibit positive drainage and eliminate areas where water might pond. SITE AND SURFACE DRAINAGE Drainage at the site should be directed away from foundations, collected and tight lined to appropriate discharge points. Consideration may be given to collecting roof drainage by eave gutters and directing it away from foundations via non-erosive devices. Water, either natural or from irrigation, should not be permitted to pond, saturate the surface soils or flow towards the foundation. Landscaping requiring a heavy irrigation schedule should not be planted adjacent to foundations or paved areas. The type of drainage issues found within 4 Leland Construction File No. I 106E4-21 November 22, 2021 the project and materials specified and used should be determined by the Engineer of Record. GROUNDWATER AND SURF ACE WATERS There was no indication of a near.surface groundwater table within our exploratory trench or perched groundwater. Although groundwater is not expected to be a significant constraint to the proposed development, our experience indicates that near~surface groundwater conditions can develop in areas where no such groundwater conditions previously existed, especially in areas where a substantial increase in surface water infiltration results from landscape irrigation or unusually heavy precipitation. It is anticipated that site development will include appropriate drainage provisions for control and discharge of surface water runoff. The type of drainage issues found within the project and materials specified and used should be determined by the Civil Engineer. The type of plants and soil specified along with proper irrigation used should be determined by the Landscape Architect. The following grading specifications should be utilized if grading is proposed. RECOMMENDED GRADING SPECIFICATIONS For Proposed Residential Building Site 2644 Jefferson Street City of Carlsbad GENERAL: Soil Testers and '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 perfonned. The 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 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 engineer will be cause for the engineer and/or his representative to immediately terminate his services. A pre-construction meeting or conference with the developer, contractor, civil engineer, soil engineer, and the agency inspector in attendance should be held at the site prior to 5 Leland Construction File No. I I06E4-21 November 22, 2021 the beginning of the grading operations. Special soil handling requirements can be discussed at that time. Grading of the site should commence with the removal of all vegetation and existing improvements from the area to be graded. Deleterious material and debris such as broken asphalt and concrete, underground pipe materials, wires, trash, etc. if encountered, should be exported from the site and should not be mixed with the fill soils. Abandoned foundations and buried septic tanks or cisterns (if encountered) should be removed and the subsequent depressions and /or trenches should be filled with properly compacted materials as part of the remedial grading. All fill and backfill soils should be placed in horizontal loose layers approximately 8 inches thick, moisture conditioned to a water content of one to three percent above optimum moisture content, and compacted to at least 90 percent relative compaction, as determined by ASTM Test Method D 1557-00. The excavation bottom should then be scarified to a depth of approximately 6 to 8 inches, moisture-conditioned to 1 to 3 percent above optimum moisture content, and re- compacted to a minimum relative compaction of 90 percent in accordance with ASTM D 1557-00. Excavated sandy or clayey soils should then be uniformly moisture conditioned at above optimum moisture content, placed in 8-inch-thick loose layers and compacted to a relative compaction of at least 90 percent. Import fill soil, if required, should consist of granular materials with low expansion potential (El less than 50 or stated by the soil engineer) and should be compacted as indicated herein. Soil Testers should be notified of the import source and should perform laboratory testing of the soil prior to its arrival at the site to determine its suitability as fill material. 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 engineer. SOIL TEST METHODS: Maximum Density & Opt Moisture Density of Soil In-Place Soil Expansion Shear Strength Gradation & Grain Size --ASTM D!557-70 --ASTM Dl556, D2922 and D3017 --UBC STANDARD 29-2 --ASTM D3080-72 --ASTM DI 140-71 6 Leland Construction File No. I 106E4-21 November 22, 2021 --ASTM D2325-68 Capillary Moisture Tension Organic Content --% Weight loss after heating for 24 hours at 300° F and after deducting soil moisture. LIMITING SOIL CONDITIONS: Minimum Compaction Expansive Soils Insufficient fines Oversized Particles 90% 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. Expansion index exceeding 20 Less than 40% passing the #4 sieve. Rocks over 10" in diameter. PREPARATION OF AREAS TO RECEIVE FILL: Brush, trash, debris and detrimental soils shall be cleared from the areas to receive fill. Detrimental soils shall be removed to finn competent soil. Slopes exceeding 20% should be stepped uphill with benches IO' or greater in width. Scarify area to receive fill to 6" depth and compact. FILL MA TE RIAL 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 Engineer. Select fill shall be as specified by the engineer. All fills shall be compacted and tested. SUBDRAINS shall be installed if required by and as directed by and detailed by the 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 confonn to the following gradation: Sieve siz.e: 3/4" %Passing: 90-100 #4 25-50 #30 5-20 #200 0-7 Subdrains shall be set at a minimum gradient of 0.2% to drain by gravity. 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 7 Leland Construction File No. 1106E4-2 I November 22, 2021 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 Maximum Expansion Index Minimum Angle of Internal Friction Cohesion Intercept 90% 30 33 Deg 100 psf UNFORESEEN CONDITIONS: 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 engineer's services for any reason, his fees up to the time of termination become due and payable. If it is necessary for the engineer to issue an unfavorable report concerning the work that he has been hired to test and inspect, the engineer shall not be held liable for any damages that might result from his 'unfavorable report'. If we can be of any further assistance, please do not hesitate to contact our office. This opportunity to be of service is sincerely appreciated. Respectfully submitted, Chin C. Chen, RPE C34442 CCC/mlj 8 ,ROFEs CH!f\l -..:: ~ -;t.. 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