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Geotecbnical lnvestigation <br />4129 Crtand Avrnue, Everctt, WA <br />July 14, 2000 <br />Subsurface Conditions <br />WFS7ERN GE07ECERJICAL CONSULTANI'S,1NC. <br />(Page 2 of 6) <br />Subsurface conditions at the site were evaluated by obsaving the excavation of 2 test pits <br />on July 6, 2000. The appro�t►ate locations of the test pits are shown on the auached Site <br />Plan, Figure I. The test piu were roughly located in the field from the stalces set to <br />delineate the house boundaries. <br />The soils encountered in the test pits were classified using the Unified Soils Classification <br />System (USCS) and are described below. <br />The test pit excavations revealed appro�rimately 8.5 feet of PEAT (Pt by USCS) below the <br />ground surface in TP-1 and 4.5 feet in TP-2. The PEAT is very soft and highly <br />compressible. In both test pits the PEAT was undalain by fine to medium SAND (SP by <br />USCS), which appeared to be in a compact wndition. A layer of Silty SAND (SM by <br />USCS) was encountered in TP-I at a depth of about 10 feet, but was not found in TP-2. <br />Ground water seepage was encountered at approximately 10 feet in TP-1 and at 7 feet in <br />TP-2. <br />Conclusions and Recommendations <br />C'.eneral <br />Based on our geotechnical engineering investigation, we conclude that the site will be <br />suitable for relocating the house provided our recommendations and good wnstruction <br />practices are followed. The PEAT (Pc) soils are not suitable for support of the house <br />foundation. The house foundation should therefore be founded on piers that extend into <br />the native SANDS (SP) encountered in the test pits to Vansfer foundation loads below the <br />peat layer. As an alternative to a pier foundation, the PEAT soils could be removed and <br />replaced with quarty spalls up to the initially planned foundation subgrade ►evel. <br />The follo�ving section contains specific recommendations for foundation support. <br />Foundation Support <br />Pier Foundation Support <br />Piers founded in firm sands will be suitable for support of the house foundation. We <br />recommend that minimum 18-inch-diameter reinforced concrete piers be installed with a <br />minimum embedment of 2 feet into the compact SANDS that were encountered in the <br />site test pit exploration. We anticipate the spacing of the piers will be 8 to 9 feet on <br />center. For design purposes, and given the pier size and embedment depth, we <br />recommend a maximum net allowable load of 5000 pounds per pier for long-term loading <br />conditions. The term net allowable load refers to the load that can be impos�:d on the <br />