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-1(11711(11_• 1J, 2004 Pcige 54 <br />Recoverability ofreserves in L-Scam are less certain because the slide plane is below the <br />L-Scam in some areas. The slide plane was identified in 90% of the characterization boreholes. <br />Although the overburden thickness and undulation ofthe bedding varies, the depth of the slide <br />plane averages 96 ft below ground. In only one borehole was the slide plane identified below the <br />L-Seam. Therefore, it is estimated that most ofthe 1.-Seam will be recoverable. <br />Note that there could be significant uncertainties in these estimates. Only nine boreholes <br />have been placed through the landslide. f'he uncertainty is estimated "fable I by the (f) values. <br />The reserves least likely to be recovered are along the edges of the landslide. The ground has <br />been bulked upward on the east side of the landslide near the G-Dip cut. This area may be <br />mostly rubble above the 1,-Seam, but insufficient data are available for confirmation. Similarly, <br />the shear mounds seen on the west side of the landslide are expected to be disturbed, but the <br />degree of intermingling above the L-Seam is highly uncertain. Where the landslide has plowed <br />the old G-Strike Pit spoils, the rock is expected to be very loose. Excavations in this area will <br />likely result in comingling of the layers, including some of the coal reserves. The rock mass <br />condition at the hill crest beyond the mapped cracks is uncertain because additional large-scale <br />fracture openings may, not be visible on surface as cracks. <br />5.4 'Truck & Shovel Cut Face Stability and Monitoring <br />Ground conditions in the K-Pit and G-Pit areas are not expected to be similar to normal <br />highwall stability conditions. The rock within the landslide perimeter has been disturbed and, <br />thus, is expected to be less stable when excavated, consequently steep cut faces should not be <br />used in disturbed areas. <br />The strategy of mining from Nest to east is favorable for gcotechnical conditions. <br />Removal of the slope crest improves stability of the remaining material. Decreasing the weight <br />at the crest reduces driving forces on the landslide. The eastward advance is down-dip of the <br />beds. Weak bedding planes plunge into the cut tace thereby having minimal effect on face <br />stability. <br />The northern portion of K-Pit will be outside the landslide limits. The borehole logs in <br />that area (figures 12 and 13) indicate RQD values of40-100 and RMR values of6075. These <br />values are typical of other areas successfully mined. Removing interhurden using dozers in this <br />area may require more than rippers to loosen the rock. Bench blasting may be needed, especially <br />for the massive sandstone units. <br />The K-Pit cuts will be on steep beds for which the orientation transitions from northerly <br />to northeasterly and back to northerly as mining moves eastward. The cross section schematic, <br />shown in Figure 38, illustrates what mining in this area might look like. Dozers can push <br />interburden either parallel to the face or down the cut thee. The geologic structure on the cut <br />face is expected to favorably oriented downdip where the potential for loose blocks rolling off <br />the cut face is expected to be minimal. It is recommended that the cut face slope not exceed <br />1 I I: I V (45°). <br />The first eight to ten K-Nit cuts within the landslide are expected to be in the rubble <br />material above the [,-Seam. It is anticipated that little blasting will be necessary in the rubblized <br />A ,ap ito Associates, Inc.