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-5- <br /> <br />methods are used. These investigations included field density tests made in <br />existing spoil and haul roads, numerous measurements of angle of repose, and <br />large gradation analyses of overburden spoil. This experience was used to aid in <br />establishing representative spoil material properties for stability analyses. <br />SPOIL PROPERTIES <br />The Coiowyo Coal Mine operates using a surface, strip-type mining <br />procedure in an open pit. The proposed Nest Pit will be an extension of the <br />existing mine. We believe the overburden which will be developed as excess spoil <br />will be very similar to the materials presently being mined. To evaluate the <br />nature of the overburden which will be used to construct the proposed excess <br />spoil, we sampled spoil from the current operation. Specific gravity tests were <br />used to measure the unit weight of representative spoil materials. Point Load <br />tests were used to estimate compressive strength. We focused on outcropping <br />sandstones available near the disposal site and the light gray or banded (varved) <br />sandstones found within the existing pit. Table l3-2 presents a summary of our <br />laboratory tests. The purpose of this testing was to establish characteristics of <br />the potential spoil materials and to evaluate materials which could be used for <br />construction of underdrains. Two-cycie, slake-durability tests were performed to <br />evaluate the durability of available drain rock. Acidity (pH) was measured on the <br />water from the slake-durability test. <br /> <br />