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./anucrrv 15, 2008 Page 39 <br />• Though the stratigraphy is well known. it is quite variable. It is not uncommon for layer <br />thickness to change within 100s of feet and to pinch-out. The model grouped geologic <br />layers by similar properties and accounted for the variable thicknesses and elevations by <br />extrapolating the geology from the nearest stratigraphic log summaries. <br />• The hods significantly steepen in the K-Pit area. Though the average bedding dip is <br />about 13°. there are local areas were the bedding dips up to 25°. The model simulated <br />this large-scale variation by interpolating coal seams elevations from CAI) sections of <br />seam contours and aerial topography. <br />• The mining of the G-Strike pit preceding G-Dip pit was significant because G-Strike was <br />downdip ofthe hillside allowing induced stresses to arch around the G-Strike cut. These <br />stresses were disturbed by G-Dip mining which was simulated in the model. <br />Successful simulation of the landslide relied on calibrating properties to known <br />displacements and tailure from the September 2005 failure in the old G-Strike Pit. The <br />groundwater table and weak I.-Roof mudstone rock properties were adjusted so that the <br />simulated tailure reasonably matched monitoring data and visual observations. Figure 27 shows <br />the estimated failed region as predicted by displacements and inelastic failure region. When <br />Agapito Associates. Inc. <br />Figure 25. Landslide Slope Failure at G-Dip Nit in October 2006