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Mr. Jim Herron, MLRD January 30, 1984 Page 3 <br /> Table 3 <br /> Unconfined Shear (16/f t3) <br /> Material Comp. Str. (psi) Str. (psi) Density <br /> Mancos Shale 13,6951 68502 168.1 <br /> Limestone/Cement Mix3 5,352 1062 139.7 <br /> 1 from Robbins tunnel bore tests <br /> 2 approximate--taken as 50% of unconfined compressive str. <br /> 3 from USBM core tests of material in place <br /> ROCK PROPERTIES <br /> Rock properties for the Mancos Shale were taken from the Robbins core test <br /> data. The shear strength was reduced from the unconfined compressive strength <br /> and estimated as half of the compressive strength. The roof, floor and ribs <br /> at the seal locations all consist of shale. <br /> Table 4 <br /> Tunnel Area (ft2) Perimeter (ft) <br /> North 165 50 <br /> South 190 54 <br /> The strength properties presented in Table 3 were determined from the <br /> laboratory tests and may not represent actual field conditions where fractures <br /> could be present. To be conservative in the design, a scaling factor of 4 was <br /> used to estimate the rock shear strength from the laboratory values. <br /> SEAL DIMENSIONS <br /> Using; the design forces with a safety factor of three and with a minimum <br /> shear strength of 1700 psi (which was scaled down four times lower than the <br /> laboratory values), the seal dimensions were determined. <br /> Removal of the loose and fractured material around the location of the <br /> seal will increase the seal shear perimeter length. In selecting the seal <br /> length a shear perimeter length of 56 feet was used for all locations. <br /> SEAL DETAILS <br /> Mine seals will have a tapered plug shape and be built with limestone/ <br /> cement material. Typical seal plan and sectional views and also a typical <br /> section of the mine seal are shown on the included sketch. <br />