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N <br />Q <br />d <br />N <br />N <br />d <br />a` <br />d <br />0 <br />0. <br />Figure 1. Summary of Pore Pressure Monitoring <br />2.0 <br />— <br />tVwR01 <br />— �VwR02 <br />VWP -01 damaged <br />between 11/22/05 <br />0.0 <br />— . —VWROS — <br />and 1/11/06. <br />—e— VwR04 <br />CIF VWR05 <br />8.0 <br />- <br />- -- <br />6.0 <br />4.0 <br />2.0 <br />0.0 <br />2.0 <br />5/28/05 7/17/05 9/5/05 10/25/05 12/14/05 2/2/06 3/24/06 <br />Monitoring Date <br />It is difficult to comment on the implications of the observed pore pressures at this time. The <br />pore pressure magnitudes observed in the field are less than those observed at failure for similar <br />confining pressures in the triaxial shear tests. That is not to say that there is no concern for the <br />observed pore pressures. No consistent changes in pore pressures have been observed to date <br />among the five piezometers. Stability of the stockpile will be significantly affected by the <br />increase or decrease of the pore pressures. Factors affecting the pore pressures include: <br />➢ Hydraulic conductivity of the coal waste. Overall, the hydraulic conductivity of the <br />waste is considered to be low. This means that pore pressures will dissipate slower than <br />for material with higher hydraulic conductivity. <br />➢ Length of drainage path. The longer the drainage path, the longer that dissipation of <br />pore pressures will take. The drainage path can be decreased, if necessary, by <br />installation of horizontal or vertical drains in the waste stockpile. These drains could be <br />sand /gravel drains, perforated pipe drains, wick drains, or other geocomposite drains. <br />➢ Rate of loading. Increased loading (i.e., placement of coal waste) will increase pore <br />pressures. The rate of placement should not be so quick that pore pressures increase <br />rather than dissipate. This rate of placement depends on the hydraulic conductivity and <br />length of drainage paths. <br />➢ Coal waste placement practices. If coal waste is compacted with high moisture contents <br />(especially above the optimum moisture content), this moisture is "locked" into the <br />waste until it is allowed to drain. Drainage may take months or it may take many years. <br />Bowie No 2 Gob Pile Stability Dec2005 <br />Project #05- 126 -GEO <br />Page 12 of 18 <br />