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Page 21 <br />l 5.2.2 Analysis Results <br />The horizontal and vertical stress contours and yield zones after solution mining and sub- <br />sequent caving aze presented in Appendix B. The results show that stresses in the caving zone <br />are greatly relieved. The plastic yield zones occur mainly within the caving azea and azound the <br />wall of the solution cavity. <br />The horizontal strains at locations of interest are presented in Figure 5-3 and 5-4. The <br />shape of the strain profiles agree with the typical horizontal strain curves, with the maximum <br />strains occurring at the point of break and zero strain at the edge of the opening. The results indi- <br />cate that the mining induced strain for the aquitard (R-6), aquifer, and "Mahogany Zone" are all <br />less than 0.005 and, hence, meet the evaluation criteria. Horizontal strains predicted from the <br />two 800-ft panels analysis aze also lower than 0.005. <br />The surface subsidence predicted from the analyses aze shown in Figures 5-5, 5-6 and <br />5-7. The maximum subsidence and horizontal displacement aze predicted to be less than 2 ft <br />above the single panel and approximately 3 ft over the two panels. The subsidence prediction <br />from a continuum model may not be conservative. An empirical approach for prediction of sur- <br />face subsidence based on the influence function is presented in Section 5.3. <br />Quantification of the impact of mining on the hydraulic conductivities of the aquifer and <br />aquitard was conducted based on the influence of the stress change on hydraulic conductivities of <br />the aquitard (R-6) and the B-Groove aquifer. The method uses the hyperbolic normal stress clo- <br />sure relationship (Goodman 1976) and the cubic flow rule in the fractured rock mass (Snow <br />1960. The description of the method and application to the White River Nahcolite, Inc. high- <br />extraction solution mining case is presented in Appendix C. The changes in hydraulic conductiv- <br />ity in the overlying R-6 and B-Groove beds are insignificant compared with the natural variation <br />of the hydraulic conductivities. <br />5.3 Surface Subsidence Prediction <br />In addition to the surface subsidence estimates discussed above, a numerical subsidence <br />prediction program was used to predict the long-term maximum possible subsidence based on the <br />extraction of 16-ft equivalent thickness nahcolite. Figure 5-8 shows the location and orientation <br />of the two panels assumed mined to 40% final extraction. <br />Agapito Associates, Inc. - <br />