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l <br />Morrison Knudsen Corporation <br />• July 10, 1996 <br />~ Page 2 <br />While the project is technically feasible, all construction on this site will have some risk of <br />distress due to the moisture-volume sensitivity of the clay. However, using the ancient landslide <br />area for the majority of the surface facilities is considered better than disturbing the surrounding <br />steeper, metastable rock slopes. Recommendations are provided in the attached report to <br />minimize the risk of potential soil movement. In general, site grading that limits the extent of <br />cuts and fills on existing slopes will result in less maintenance over the life of the project. <br />Effective surface drainage design and drainage of filled areas will help to assure stable moisture <br />content of the subgrade and thus better structure performance. <br />Most foundations placed below soil zones subject to moisture increase can be designed for <br />relatively high bearing pressures, with only a low risk of damaging differential movement. <br />Floor slabs on grade can present more risk of movement because dead load is usually low. <br />Steep slopes in the clay are possible temporarily. Because of the forces of weathering and <br />gravity on the clay, slopes will loose internal strength and creep or fail unless inclined <br />moderately or mechanically retained. Somewhat different design criteria are recommended for <br />cut and fill slopes. The site soils are considered poor pavement subgrades. Pavement design <br />criteria are given for the haul road to accommodate heavy truck traffic. We have not studied <br />the geotechnical impact of moving the lower portion of the haul road off of the landslide area. <br />• The site soils are considered generally good for pond lining for relatively stable water levels. <br />The report which follows summarizes our findings and presents our conclusions and <br />recommendations. It is important that we provide consultation during design, and field services <br />during construction to review and monitor the implementation of the geotechnical <br />recommendations. This study utilized widely scattered boring locations to explore the general <br />subsurface conditions. Once structure locations are finalized, additional subsurface exploration <br />may be appropriate to generate final design criteria, particularly in deep filled areas. <br />If you have any questions regarding this report, please contact us. <br />Respectfully submitted, ,~~~~u~nt±.nrn' _r~,~r,/'~ <br />,.u .,; <br />c° <br /> , <br />:~.,; <br />TECHNOLQGIES;'IN~: ~° `:; <br /> <br /> <br /> ;~ i i!'~tp ems` <br /> 7 <br /> <br />David A. Glater, P.E. <br />Reviewed by: <br />• David H. Adams II, P.E. <br />DAG/kv <br />Enclosures <br />