Laserfiche WebLink
3.3.2 Near seam intact strength and structure <br />Figures 7, 8, and 9 present detailed geotechnical logs for TC-03-01, TC-03-02, and TC- <br />03-03, and include lithology, structure, and material properties near the Upper B Seam. <br />The structural log indicates the location of geologic discontinuities (including both <br />natural and drilling-induced fractures). Much additional data regarding the condition of <br />discontinuities (including roughness, aperture, and spacing) were collected, but were <br />excluded from these logs for clarity. This data is used in .the following sections for <br />calculation of RQD and Rock Mass Rating. <br />With the exception of two samples from the immediate roof, most of the roof and floor <br />rocks have moderate to high strength. The minimum tested uniaxial compressive <br />strength (1260 psi) is reported for a stiff but jointed siltstone at TC-03-03. The presence <br />of a vertical joint on this sample has caused a drastic reduction in strength. This assertion <br />is based on a review of point-load tests taken immediately below this horizon in which <br />• <br />the sample exhibited four times more strength (7390 psi) in the horizontal direction <br />(diametrical) than the UCI value. <br />The Upper B Seam is the weakest member of near-seam strata. Perhaps, the cleated <br />nature of coal samples has contributed to some very low uniaxial compressive strength <br />values at TC-03-01 and TC-03-02. However, because the coal seam thins to the west <br />near these coreholes, these low strength values may be related to changes in the <br />depositional environment as discussed in section 3.1. The uniaxial strength values are <br />higher to the east approaching approximately 2,000 psi. Overall, UCI test values average <br />1250 psi which is approximately 50% lower than average values for the B Seam in the <br />basin (Maleki and others 1999). MTI has observed similar, abnormally lower strength <br />properties for the D Seam in neighboring operations, but the cause (s) of strength <br />reductions is not known at this time. This lower strength, however, is accounted for in <br />calculations of in-situ pillar strength. <br />• <br />Maleki Technologies, Inc. Page 17