Laserfiche WebLink
4. Slope Stability <br /> The slope stability of each zone was analyzed previously as part of the designs approved in TR <br /> 02. Zones 2, 3A, and 4 have all been installed to the cross sections outlined in TR 02. The cross <br /> sections developed were staked in the field as grade targets and matched by construction crews <br /> with GPS controls in most areas. Zone 3B is the only zone that has a different cross section than <br /> that approved in TR 02. Zone 4 does not have all of the upper drainage pipe as originally <br /> proscribed. <br /> Zones 3B and 4 have thus been re-evaluated for slope stability based on the changes made during <br /> construction and meet the required criteria. <br /> 4_1 Zone 3B <br /> Zone 3B has a distinctly different final grade than originally anticipated along with a different <br /> configuration of subsurface drainage pipes. The pipe layout can be seen in Figure 3. The primary <br /> change being the raising of the Zone 3B Upper Pipe to a higher elevation to accommodate <br /> construction. <br /> 4.1.1 Slope Stability Analysis <br /> Using final grade surveys and measurements of material thickness, a new cross section was <br /> developed. This cross section XO can be seen on Map C-6B. This cross section was then built <br /> into a slope stability model in GALENA software. All GALENA data results can be seen in <br /> Appendix 3. <br /> Two fundamental assumptions guided the slope stability analysis: <br /> 1. All identified materials are homogenous in their respective layers. <br /> 2. The piezometric surface exists on the shale contact, and only intermittently. <br /> 4.1.1.1. Material Homogeneity <br /> The first assumption is based on the thorough data collection onsite that has identified the <br /> present earth materials and their distribution. While no sampling regime is perfect,the regular <br /> reports from Ground Engineering's technical support staff show no concerning variation in either <br /> material properties or placement. As is to be expected in earthwork,the exact thickness of <br /> different material layers varies, but their order(tailings atop colluvium atop shale) is consistent. <br /> The extra deep amount of material at both Z3B pipes merely shows that the true thickness of <br /> tailings in those areas was greater than originally assumed. This is likely representative of a local <br /> valley fill created by the original tailings dumping in this area. Valley fills have been a common <br /> method of dump construction, and as such it would not be a surprise that such a thing was the <br /> case in Zone 3B. <br /> 4.1.1.2. Piezometric Surface <br /> The second assumption,that the piezometric surface exists on the shale contact only, is based on <br /> several observed site conditions. First, prior to the presence of the stormwater ponds along the <br /> slope,the tailings fill appears to have been stable based on historic aerials and APC interviews. <br /> Second, Ground Engineering investigation prior to and during repair work found no sign of <br /> standing water within the slope area where the tailings fill was. Third, during construction, no <br /> Ralston TR 03 9 Greg t.ehicki and Associate%n.►.c <br />