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MINING AND RECLAMATION PLAN January., 1986 <br />MT. GUNNISON N0. 1 (NINE . <br />Rock Properties - R~~ck properties for the F seam coal and the layers in the roof <br />and floor were taken from Mt. Gunnison core test data. The shear strength were <br />reduced from the un~:onfined to compressive strength, and discussed ~in the <br />Reference 2, and estimated as half of the compressive strength. The roof and <br />floor layers consists of shale, siltstone and sandstone. The strenyth of rock <br />layers increases consistently away from the F seam openings. But the strength <br />data within five feet of the mine opening, the strengths of which are low, were <br />used in the design ~rnd the strength properties are summarized in the Table <br />3.5.2.72. <br />The strength propert:ies presented in the Table 3.5.2.72 were determined from the <br />laboratory tests and may not represent actual field conditions where fractures <br />could be present. ''o be conservative in the design a scaling factor of 4 was <br />used to estimate they rock shear strength from the laboratory values.. This scale <br />factor is conservative when compared to the recommended scale factors by W. A. <br />Hustrulild, Reference 2. <br />Seal Dimensions - Using the design forces with a safety factor of tFiree (Table <br />3.5.2.71) and with z~ minimum shear strength of 500 psi (which was sealed down <br />four times lower thz~n the laboratory values), the seal dimensions were <br />determined. The sez~l dimension estimates for different locations were taken <br />based on the design curves shown in the Exhibits 3.5.2.E3 through 3.5.2.E5. <br />The design curves show a relationship between the shear perimeter length, which <br />is the perimeter of the mine opening at seal location and require seal lengths <br />for various shear strengths. The shear perimeter length for the proposed mine <br />opening of 8 feet high and 20 feet wide is 56 feet. <br />Removal of the loose and fractured material around the location of the seal will <br />increase the seal shear perimeter length. In selecting the seal length a shear <br />perimeter length of 80 feet was used for all the locations which is almost 40 <br />percent higher than the proposed mine openings. The seal dimensions at <br />3-86 <br />