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4 <br />• 3.75 the roof is a massive sandstone while in Drill Hole 8A <br />the roof consists of a variety of rock types. Good roof bolt <br />anchorage is envisioned, owing to the existence of sandstones <br />or sandstone, siltstone, claystone interbeds at 4 to 6 feet <br />above the Upper Wheeler Seam. Cavability in the gob areas is <br />estimated to be moderate, owing to the strong and massive nature <br />of many of the rock units and the moderate to high RQD's. <br />Upper Wheeler Seam. The coal is fairly solid and strong in <br />many cases, but tends to break along cleats, as should be expected. <br />The presence of the cleats at angles of 20° to 40° to the core <br />axis may cause some pillar stability problems in terms of rib <br />slabbing. The exact effects and remedial measures to handle them <br />need further study. <br />Interburden. The interburden strata is of moderate strength, <br />moderate RQD and there are a number of geologic discontinuities <br />such as joints and compressional slickensides. The percentage of <br />higher modulus material, such as sandstone, is very low and there <br />is a moderate number of interbeds. The bearing capacity and usage <br />of the floor, as a mining base during upper seam mining, should <br />not present major problems although some rutting and slipping <br />could occur. The immediate strata above the lower seam is carbon- <br />aceous claystone and it may give quite variable roof competency <br />conditions. However, at best, it will require support and possible <br />• protection from moisture. <br />Lower Wheeler Seam. The coal is generally fairly solid and <br />strong and is quite similar to the upper seam from a strength <br />standpoint. Geologic discontinuities, in the form of cleats, <br />yield breaks at angles varying from 0° to 35° to the core axis. <br />Lower Wheeler Floor. The immediate floor materials are <br />carbonaceous claystones which may rut and be slick when they are <br />wet. However, the overall floor bearing capacity is probably <br />very good due to underlying strong strata beneath the carbonaceous <br />claystones. <br />Summary. The upper seam roof should be fairly strong, <br />solid and competent, and support with standard spaced roof bolts <br />should be adequate. Cavability in gob areas should range from <br />fair to good. Coal strengths are similar in both the upper and <br />lower seams and pillars should be fairly stable in both cases, <br />except for some possible rib slabbing. Interburden characteristics <br />are described as low modulus with moderate interbeds. Further, <br />the floor of the upper seam may rut, but should be stable overall. <br />The lower seam roof will require more support than the upper seam <br />roof. The lower seam floor may have some rutting, but will be <br />generally stable. <br /> <br />$EEGMILLER INTERNATIONAL <br />