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• After cooling, the thickness of the zone of failure in the wall is diminished suggesting that <br /> failure will not propagate after cooling. Based on the analytical results, it appears that <br /> cooling will promote long-term stability. Upon cooling of the brine, nahcolite should <br /> precipitate out and tend to reheal fracturing and promote stability. <br /> • The same conclusions apply to the structural stability of a 225 foot diameter single <br /> cavern as do apply to the 125 foot diameter single cavern. Results of analyses for the <br /> 225 foot diameter cavern suggested wall slabbing and a small zone of shear failure in <br /> the roof near the roof/wall intersection. These zones of failure were very similar to the <br /> results from the 125 foot diameter cavern. <br /> • The results suggest that cavern roof and wall stability are insensitive to diameter <br /> variations for the range of cavern diameters analyzed (125 feet to 225 feet) and <br /> exemplifies the stabilizing effect the fluid pressure and residual solids within the cavern <br /> have on cavern stability. <br /> The stability of multiple caverns also was evaluated to assess pillar stability within the well <br /> fields. Multiple cavern stability was analyzed for the proposed six well field (125 foot to 225 <br /> . foot diameter caverns on 350 foot spacings). A 330 foot barrier pillar was assumed <br /> separating the well fields. Ultimately, well field pillar stability will determine the impact on <br /> overlying aquifers and surface subsidence. <br /> • Evaluation of the structural stability of the proposed six well layout on 350 foot centers <br /> indicate that pillars between caverns will remain stable during and after solution mining <br /> for cavern diameters ranging from 125 foot to 225 ft. Although analyses predict pillar <br /> core temperatures will approach the injection temperature of 250°F for the 225 foot <br /> diameter cavern, the confinement provided by the fluid pressures within the caverns <br /> stabilizes pillar material preventing failure. As was true in the single cavern stability <br /> evaluation, cooling of the cavern appears to enhance stability and promote long-term <br /> stability. <br /> • The 330 foot barrier pillars are structurally stable for the geometries analyzed (125 foot <br /> to 225 foot diameter caverns on 350 foot centers). Load transfer to the barrier pillars <br /> would not become significant unless yielding or pillar failure occurred within the well <br /> field. <br /> Hardy and Goodrich (July, 1996) also concluded that measurable subsidence over the <br /> proposed six well field (125 foot to 225 foot diameter caverns on 350 foot centers) is unlikely <br /> GAAM78545.00ZMinePWn%MINEPLAN.DOC 4-17 <br />