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�tl <br />` !Huddlegatt-Bern <br />� 4'su'etS fe] -5.111 <br />3.0 LABORATORY TESTING <br />As indicated previously, the original evaluation of gob pile #3 was based upon <br />laboratory testing results for material from gob pile #2. In order to re- evaluate gob pile <br />#3, HBET collected samples of blended material from gob pile #3. Consolidated - <br />Undrained triaxial shear testing with pore pressure measurement was subsequently <br />completed. The testing results are included in Appendix A and indicated a fully drained <br />friction angle of 30 °. <br />4.0 STABILITY ANALYSES <br />4.1 General <br />In order to evaluate the stability of the existing gob pile #3, HBET utilized cross <br />sections generated by J.E. Stover and Associates. A plan of gob pile #3 with locations of <br />cross sections is included as Figure 1. Cross Section B -B' includes the highest gob. In <br />addition, Section B -B' includes the largest depth of cut. As a result, this section will be <br />critical and was analyzed as part of the current evaluation. Analysis of the gob pile was <br />completed utilizing the GeoSlope GeoStudio 2007 SLOPE/W software package. Based <br />upon our experience with stability modeling and upon our previous work at the Bowie <br />No. 2 mine, HBET used the Spencer method in our analyses. <br />4.2 Soil Parameters <br />Soil parameters used in the stability analyses were selected based upon <br />information in the referenced documents and recent laboratory testing. As indicated in <br />the referenced report, both total stress ( undrained) and effective stress (drained) <br />conditions were assumed in the analyses. However, based upon years of pore pressure <br />data for gob pile #2 which indicate that undrained conditions have not developed in gob <br />pile #2, HBET does not believe that undrained conditions will develop at gob pile #3. As <br />a result, HBET only completed drained analysis of proposed gob pile #3. However, pore <br />pressures should be monitored over time as a sharp increase in the pore pressures over a <br />short time could indicate that undrained conditions are developing which may result in <br />instabilities in the gob pile. <br />The parameters used in the analyses are discussed in the following sections. <br />Contracted Gob <br />The referenced report indicates that a wet unit weight of 112.5 pcf was used in the <br />previous analyses. However, recent evaluation of gob pile #2 indicated that a unit weight <br />of 104.6 pcf is more appropriate for the gob. In the absence of available data for gob pile <br />#3, the lower, more conservative unit weight was used in the analysis. <br />\12605 ALL PROJHCTTW489 • JE SW%er Associates 1=10W89 -0003 Bewde \tine1200 • Gt$" 3ARMsion PM89.0003 8052114 R2 doe 2 <br />