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4.0 DESIGN ANALYSIS Two basic geometries were analyzed using the finite-elemen[ code JAC (Biffle, 1984) to simulate the 100 and 125 ft diameter cavities. The mesh in the vicinity of the caverns is shown in Figure 6. For some analyses, elements in the roof of the cavity were removed to evaluate the stability of the arched roof after local roof fallout. Both linearly elastic and yielding material models were used with the propetties listed in Table 1 assigned to the zones identified in Figure 5. 4.1 SPAN EVALiJATION FOR A CYLINDRICAL CAVITY The safety factors in the immediate roof for the dry and operational conditions for various rock strength assumptions are listed in Table 2. The rock strength conditions correspond to the Mohr-Coulomb strength criterion (Equation 4), and the Hcek and Brown (1988) criterion (Equation 2) for RMR == 60 and 40%. TABLE 2 SAFETY FACTORS IN THE ROOF FOR VARIOUS ROCK FAILURE ASSUMPTIONS • .,. Dry Conditions Operational Conditions Cavity Diameter Mohr-Coulomb RMR=tiO RMR=40 Mohr-Coulomb RMR=60 RMR=40 100 h 1.55 1.82 1.25 0.92 0.90 0.59 125 ft 1.45 1.59 1.10 0.92 0.77 0.49 Figure 7 shows the stress vectors for these two cases and the long-term case for both the 100 and 125 ft diameter caverns. Figure 8 shows the contours of the safety factors for the tltrce cases. lJ Tension is predicted in the immediate roof of the cavem and failtue above the cavity wall under the operational conditions. A nonlinear analysis using the worst case (weak) material propenies (RMR=40%) and the Mohr-Coulomb yield condition was run to determine if the failure above the cavity wall would expand and intersect the roof. The results of this analysis for both the 100 and 12:i ft cavities are shown in Figure 9. This analysis indicates that in both cases yield would progress through the cavem roof, suggesting that under these worst case J. F. T. Agapi[o & Associates, Inc. 16