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Mr. Max Ramey <br />.Tune 17. 200; <br />Page 7 <br />temperatwe is maintained at a constant value, as if it were in production, while the free <br />temperature scenario represents a situation where the cavern cools down. The free temperature <br />cool down did not consider the effect of a heated material within the cavity. The cavern material <br />(residual oil shale and liquor) would slow the rate of cavern cool down; hence, the actual <br />conditions are expected to be between the fixed and free conditions modeled. <br />The strength of the rock mass is expected to decline with pressure cycling. No cycling <br />tests have been completed on oil shale or nahcolite, so literature sources for testing of rock wider <br />cyclic loading was referenced. Cho &Haimson' (1987) found that ten ore inure pressure cycles <br />reduced the rock strengths fom 0.9 to 0.7 ofpre-cycled strengths. A conservative case in which <br />the rock strengths were reduce to 0.8 of original values was modeled to evaluate the effect of the <br />pressure cycling on the depth of yield in the roof and walls of the cavern. <br />MODEL RESULTS <br />In this study, cases with varying cavity temperatures, pressures, and sizes were modeled. <br />Internal cavern pressure was varied from 900 to 100 psi to analyze the effect of pressure on <br />cavern stability. Also, the cavern diameter was varied tl•om 0 to 300 tt to capture the <br />interrelationship between cavern width, pressure and stability. Cavity temperatures of 350°F and <br />420°F were also modeled as unique cases. Table 3 lists the depth of yield in the roof and cavern <br />walls for the many cases analyzed. <br />Predicted temperatures, mechanical stability factors of safety, and yield zones in the <br />vicinity of the soht[ion cavity are shown in Figures 7 to 9 for 200-fr-diameter caverns after <br />sohrtion mining and at the beginning (900 psi) and end (100 psi) of depressurization. The depth <br />of yield fora 300-ft-diameter cavern under the same pressure conditions is shown in Figure 10. <br />The depth of yield plots (Figures 9 and 10) show the extent of yield in any prior <br />increment of cavity growth. In the safety factor (SF) plot (Figure 8), the area with a SF equal or <br />less than 1 indicates the area where yield is active in the immediate last step of analysis. When <br />the cavern is depressurized or the cavern diameter is expanded, additional areas may be added <br />where yielding has occurred. <br />Figures 11 and 12 are summary plots showing the depth of yield into the foof and wall of <br />the cavity in response to these and other cavity width-pressure-temperauue scenarios. In tlrese <br />figures, the depth of yielding is contoured as a function of both cavern width (~-asis) and cavern <br />pressure (y-axis). <br />The depth of yield in the roof caused by pressure cycling for conditions is summarized in <br />Figure 13 for both the 350°F' case and the hot 420°F case for [he fixed cavern temperature and <br />the cooling (free) cavern cases. For the 350°F case, the depth of yield in the cavern roof is shown <br />' Cho. T. F. and B. C. Haimson (1987), "Effect of Cyclic Loading on Circular Openings -Results of a Laboratory <br />Simulation," 28°i U. S. Symposium on Rock Med~anica~. Tucson, AZ, June 29°' through July I", pp. SOi-813. <br />Agapito Associates, Inc. <br />