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Page 18 <br />5.0 ANALYTICAL EVALUATION OF PROPOSED MINE PLAN <br /> <br />5.1 Introduction <br />Numerical analyses were conducted to evaluate the potential impact of mining on overly- <br />ing strata. The scenario with cavern width extending to 800 ft was simulated using two- <br />dimensional plane-strain finite difference analysis techniques. An analysis was also completed <br />for two panels sepazated by a 200-ft barrier pillar. The stresses and deformations predicted for <br />the aquitazd, the aquifer, and the "Mahogany Zone" were evaluated against the design criteria <br />summarized in Section 4.3. A surface subsidence prediction based on the integration of an influ- <br />ence function is also presented as an indication of long-term subsidence from potential high- <br />extraction solution-mined panels. <br />5.2 Two-Dimensional Finite Difference Analysis <br />5.2.1 Strati2raphv and Model Parameters <br />I The stratigraphy reported for core hole NaTec 26-88-1 (Agapito Associates, Inc. 1988), <br />presented in Table 2-2, is used for representation of the in situ condition in the analysis. The <br />stratigraphic units and their related geomechanics properties used in the analysis are listed in <br />Table 5-1. The geomechanics properties include Rock Quality Designation (RQD), intact elastic <br />and rock mass elastic moduli, and Poisson's ratio. The rock mass Poisson's ratio is assumed to be <br />equivalent to the intact value. Reduction factors for the rock mass inhomogeneities in elastic <br />modulus were calculated based on the RQD and the formula proposed by Baczynski (1982). The <br />reduction factor ranges between 0.1 to 0.2 for the lower RQD category rock and 0.5 to 0.75 for <br />the good RQD category rock. <br />Two scenarios for caving were simulated in the finite difference analysis. The first one <br />assumes caving occurs within the saline zone with a bulking factor of 1.3. The second scenazio <br />extends the caving zone to R-5 with a smaller bulking factor of 1.1. The thicknesses of the cav- <br />ing zone were predicted to be 50 and 160 ft for the two scenarios, respectively. The calculation <br />of the caving zone thickness is documented in Appendix A. The elastic modulus for the material <br />in the 50-ft caving zone was assumed to be 7000 psi or about IS% of the estimated in-place <br />modulus of the L-5 zone. This estimated elastic modulus was conservatively based on properties <br />Associates, <br />