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-Ia- <br />• (Sheet I, Fig. I). Our experience indicates these slides may be triggered by water <br />in fractured coal lenses which emerge from the slopes. The planned `Nest Pit mine <br />cut will, in effect, "cut off" or drain up-dip water from this slope. We recommend <br />constructing the north pit wall to limit infiltration of subsurface water into the <br />coal lenses. This can be accomplished by sloping the benches and/or placing clay <br />soil fill on the benches and over the exposed coal to direct water to the south (into <br />the pit). <br />FOUNDATION CONDITIONS <br />Foundation conditions in the area of the excess spoil disposal site were <br />evaluated by drilling I I exploratory borings (TH-I through TH-10, and TH-7A) at <br />the approximate locations shown on Fig. I and Sheet I. The placement of our <br />• borings was limited to those areas where access by struck-mounted drill rig was <br />passible. We were able to drill borings around most of the perimeter of the spoil <br />site and at the critica4 toe area in the valley near Taylor Creek. <br />In general, borings in the higher portions of this site indicated a shallow <br />mantle of sandy clay or silty sand soils underlain by interbedded claystone, <br />siltstone and sandstone bedrock. The upper portions of the bedrock were <br />moderately weathered. `Ne found thin coal lenses in borings TH-5 and TH-9. The <br />thickness of overburden soils in our borings on the higher portions of the site <br />ranged from less than I to about 6 feet. <br />Borings TH-I, TH-2, TH-7, TH-7A and TH-!0 were drilled in valley bottom <br />areas. These borings encountered 8 to about 31 feet of colluvial soils consisting of <br />sandstone and claystone fragments contained within a clay matrix. Gradation test <br />results indicated the soils classified as a sandy clay. <br /> <br />