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Farrgeotech.pdfAssociated Earth Sciences, Inc. N EE NJ 0 0 &I 6ra6nS 25'Yea PYo fSal ce August 10, 2006 Project No. ICE060516A hEET FILE P. Mr. Lance Farr 8941 179`' Place SW Edmonds, Washington 98026 Subject: Proposed Deck Footing Subgrades Farr Residence 8941 179`t' Place SW Edmonds, Washington References: Associated Earth Sciences, Inc. Site Evaluation Letter 8941 179' Place SW Edmonds, Washington Dated March 25, 1987 Associated Earth Sciences, Inc. Slope Analysis Letter RESUB 8941 179' Place SW Edmonds, Washington AUG 112006 Dated April 9, 1987 BUILDING DEPARTMENT CITY OF EDMONDS Associated Earth Sciences, Inc. Inspection of Drainage Control Measures Letter 8941 179` PIace SW Edmonds, Washington Dated May 6, 1987 Dear Mr. Farr: We understand that you propose to construct a new deck addition to your existing home at the above --referenced address. Associated Earth Sciences, Inc. (AESI) has previously provided geotechnical consulting services to assess the stability of the rock -faced slope on the property in 1987. We understand that the City of Edmonds is requiring a special inspection to assess suitable soil bearing for the new deck foundations and letter of design recommendations for the deck. The purpose of this letter is to provide geotechnical recommendations for design of the deck and confirm that we have been retained to provide geotechnical special inspection for the soils bearing, as required by the City of Edmonds. Si"TREET FILE Ki&fmd Office • 911 Fifth Avenue, Suite 100 • Kiridmd, WA 98033 -PI (425)827 -7701 -Fl (425) 827-5424 Everett Office • 29111/2 HevvittAvenue, Suite 2 • Evemm WA 98201 • P (425) 259-0522 • F 1 (425) 252-3408 wwmaesgeomm Written authorization to proceed with this study was granted by Mr. Lance Farr. Our study was based on our previous geotechnical study, conversations with you, and accomplished in general accordance with our scope of work letter dated July 17, 2006. This letter has been prepared for the exclusive use of Mr. Farr and his agents for specific application to this project. Within the limitations of scope, schedule, and budget, our services have been performed in accordance with generally accepted geotechnical engineering and engineering geology practices in effect in this area at the time our letter was prepared. No other warranty, express or implied, is made. PROJECT UNDERSTANDING We understand that the proposed deck will be located on the north side of the existing dwelling (see attached site sketch provided by the client). A rock -covered slope is situated on a diagonal from northwest to southeast, which will be adjacent to the northeast corner of the deck. The height of the slops area ranges from approximately 2 to 15 feet, with an inclination of approximately 45 to 55 degrees. We understand that a stairway was originally proposed on the west side of the deck, but that location was not allowed because of a 25 -foot rear yard setback. We understand that the City of Edmonds will allow the stairs to be located on the north side of the deck closer to the slope area if a geotechnical engineer determines that this is a suitable location. We understand that the slope area has remained stable since our 1987 studies . CONCLUSIONS AND RECOMMENDATIONS In our opinion, construction of the deck is feasible in the proposed location from a geotechnical standpoint as long as the recommendations of our 1987 study and this letter are followed. Similarly, the stairway may be located on the north side of the proposed deck close to, but not on, the slope, provided our recommendations are followed. The main issues of concern are providing suitable foundation support and minimizing surcharge on the slope area. As discussed in our 1987 studies, the rock covering should not be considered a retaining structure, but the slope should be stable under static conditions. The control of surface water away from the slope area and backfill is also important, and measures have been implemented in 1987 to that effect. We recommend that the footings for the proposed deck and stairway be supported on the native, dense sand or hard silt/clay soils underlying the existing fill soils. Based on the explorations performed for our 1987 study, we anticipate that native soils suitable for foundation support will be on the order of 5 to 6 feet below the ground surface. The footings for the deck should extend down to the suitable native soils, or the excavations should be backfilled with lean -mix or structural concrete to the design bottom of footing elevations. If lean -mix concrete is used, it should contain at least 1'/2 sacks of cement per cubic yard. Footings should be buried at least 18 inches into the surrounding soil for frost protection. 7 We recommend an allowable bearing capacity of 2,000 pounds per square foot (psf) for footings supported directly on the dense/hard native soils, or on lean-mix/concrete backfill placed directly on the dense/hard native soils. An increase of one-third may be used for short- term wind or seismic loading. Anticipated settlement of footings founded on the dense/hard native soils or on lean-mix/concrete backfill placed directly on the dense/hard native soils should be on the order of 1 inch. However, disturbed soil not removed from footing excavations prior to footing placement could result in increased settlements. All footing areas should be inspected by AESI prior to placing concrete to verify that the design bearing capacity of the soils has been attained and that construction conforms with the recommendations contained in this letter. It should be noted that the area bounded by lines extending downward at 1H: 1V (Horizontal -Vertical) from any footing must not intersect another footing or intersect a filled area that has not been compacted to at least 95 percent of American Society for Testing and Materials (ASTM):D 1557. In addition, a 1.5H:IV line extending down from any footing must not daylight because sloughing or raveling may eventually undermine the footing. Thus, footings should not be placed near the edge of steps or cuts in the bearing soils. Based on the soil conditions encountered in our 1987 study, excavation down to the native soils should provide a suitable effective setback from the face of the slope. If suitable bearing soils are found above a 1.5H:IV line extending up from the toe of the slope, we recommend that the footing excavation be extended to below such a line. CLOSURE We hope this information meets your present needs. If you have any questions concerning this letter, please feel free to contact this office. Sincerely, ASSOCIATED EARTH SCIENCES, INC. Kirkland, Washington Eric J. Lim, P. Project Engineer Attachment: Site Plan Sketch Provided by Mr. Farr FJL/ld - KE060516A2 - Projeas1200605161KEMP 3 V EKPi4ES 1 ! b f Matthew A. Miller, P.E. Associate Engineer