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GEOTECHNICAL ENGINEERING STUDY <br />Cascasia Pacific Properties, Ltd. <br />Jury 15, 1999 <br />E-8602 <br />Page 11 <br />Lateral loads can be resisted by friction between the base of the foundation and the <br />supporting soil, and by passive soil pressure acting on the face of the buried portion of the <br />foundation and grade beams. The foundation excavations must be backfilled with structural <br />fill to establish adequate passive resistance around the foundation elements. As an <br />alternative, foundations can be poured "neat" against competent native soils. Resistance to <br />lateral loads from passive earth pressures can be calculated using an equivalent fluid pressure <br />of three hundred fifty (350) pounds per cubic foot (pcf). For frictional capacity, a coefficient <br />of 0.40 may be used for foundations bearing on competent native soils, structural fill, or lean <br />mix. These lateral resistance values are allowable values, a factor -of -safety of 1.5 has been <br />included. <br />Footing excavations should be observed by a representative of ECI. Compaction testing of <br />structural fill in foundation areas should be periodically performed by ECI. <br />Pile Foundations <br />As an alternative to maintaining a minimum footing setback from the tunnel structure, the use <br />of pile foundations in the vicinity of the tunnel can be considered. Use of pile foundations will <br />serve to transfer the building loads below the bottom elevation of the tunnel, and result in no <br />increased loading on the tunnel structure. In our opinion, the piles should maintain a minimum <br />setback of ten feet from the edges of the tunnel. We recommend verifying this setback <br />distance with Burlington Northern. <br />Given the subsurface conditions encountered, and our understanding of the proposed building <br />loads, it is our opinion eighteen (18) inch diameter augercast piles can be considered. For <br />preliminary design purposes, an allowable axial capacity of ninety (90) tons can be assumed <br />for eighteer (18) inch diameter augercast piles advanced at least five feet below the bottom <br />of the tunnel structure. Based on the survey of the train tunnel, we estimate pile lengths of <br />approximately thirty-five (35) feet to forty (40) feet will be necessary to advance the piles a <br />minimum of five feet below the bottom elevation of the tunnel structure. <br />Eenh Coneuttaws. hw. <br />