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Table 4: CRSP3 Parameter Ranges for Representative Site Conditions <br />SITE CONDITION <br />Tan ential Coefficient <br />Le.n`7th <br />Restitution Coefficient <br />Min <br />Ave <br />Max <br />Min <br />Ave <br />Max <br />Sandstone Cliff Face <br />0.83 <br />0.85 <br />0.87 <br />0.33 <br />0.35 <br />0.37 <br />Road Pavement <br />0.83 <br />0.85 <br />0,87 <br />0.33 <br />0.35 <br />0.37 <br />Tallus Covered Upper Foreslo e <br />0.82 <br />0.835 <br />0.85 <br />0.30 <br />0.315 <br />0.33 <br />Thin Colluvium Overlying Marine <br />Shales on Upper Foreslo e <br />0.80 <br />0.835 <br />0.85 <br />0.30 <br />0.315 <br />0.33 <br />Colluvium Covered Lower Foreslo e <br />0.78 <br />0.805 <br />0.83 <br />0.28 <br />0,29 <br />0.30 <br />5. DAMAGE TO THE CLIFF IN THE PHASE I <br />STUDY AREA <br />The western limit of the Phase I study area, Zones 1 <br />to 3 experienced cracking, however, no massive <br />failures were observed during or following under- <br />mining. Cliff failure occurred several months after <br />undermining in Phase I Zones 4 and 5. Approxi- <br />mately twenty boulders were retained by the <br />remedial trench in Phase I, Zones 4 and 5. Table 5 <br />provides summary data for thirteen of the largest <br />blocks. Retained boulder size ranged from 10 to 900 <br />tons with an average block weight of 115 tons (1,500 <br />cubic feet). The average boulder weight was 50 tons <br />(600 cubic feet) when the largest boulder was <br />removed from consideration. <br />Table 5: Boulders Retained by the Remedial Trench/Berm <br />Boulder <br />Number <br />Type <br />Le.n`7th <br />Width <br />Height <br />Approx. <br />Volume <br />(ft3) <br />Approx. <br />Mass <br />(tons) <br />R1 <br />triangle (3) <br />34 <br />26 <br />20 <br />12580 <br />944 <br />R2 <br />disk 2 <br />8 <br />5 <br />4 <br />160 <br />12 <br />R3 <br />cube (l) <br />13 <br />15 <br />12 <br />2340 <br />176 <br />R4 <br />cube (1 ) <br />11 <br />8 <br />7 <br />616 <br />46 <br />R5 <br />disk 2 <br />6 <br />9 <br />9 <br />486 <br />36 <br />R6 <br />disk 2 <br />3 <br />4 <br />5 <br />60 <br />5 <br />R 7 <br />disk (2) <br />5 <br />8 <br />7 <br />280 <br />21 <br />R8 <br />cube (1) <br />6 <br />6 <br />6 <br />216 <br />16 <br />R9 <br />cube 1) <br />12 <br />16 <br />11 <br />2112 <br />158 <br />RIO <br />triangle (3) <br />4 <br />7 <br />4.5 <br />126 <br />9 <br />R11 <br />disk (2 <br />9 <br />9 <br />6 <br />486 <br />36 <br />R12 <br />disk (2) <br />8 <br />10 <br />5 <br />400 <br />30 <br />R13 <br />cube (1) <br />2 <br />2 <br />2 <br />8 <br />1 <br />Average <br />9 <br />10 <br />8 <br />1528 <br />115 <br />Average without 944 ton block <br />7 <br />8 <br />7 <br />608 <br />46 <br />6. REFERENCES <br />CTI, 1993. Colorado Rockfall Simulation Program <br />(CRSP), Users Manual for Version 3.0, <br />Colorado Transportation Institute, December <br />1993, <br />Pfeiffer, T.J. and Bowen, T.D. "Computer <br />Simulation of Rockfalls ", Bull. Of Assoc. of <br />Engineering Geologists, Vol. 26 1989. <br />Priest, S.D, and Hudson, J. A. "Discontinuity <br />Spacing in Rock ", Int. J. Rock Mech. Min. <br />Sci. & Geomech. Abstr. Vol. 13,1976. <br />Priest, S.D. and Hudson, J. A. "Estimation of <br />Discontinuity Spacing and Trace Length <br />Using Scanline Surveys ", Int. J. Rock Mech. <br />Min. Sci. & Geomech. Abstr. Vol. 18,1981. <br />SubTerra, Inc., 1994. Rockfall Hazard Assessment <br />and Selection of Hazard Control or <br />Mitigation Measures, report prepared for <br />Twentymile Coal Company, October, 7, <br />1994. <br />Terzaghi l R. D. "Sources of Error In Joint Surveys ", <br />Geotechnique, Vol. 15,1965. <br />