2001-12-11_PERMIT FILE - C1980007A (2)

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April 1989 A summary of immediate roof and floor test restclts is shown in Tables 3.4.A.9, 3.4.A.10 and 3.4.A.11. Table 3.4.A.9 compares uniaxial compressive strength test data between previous studies and the present study. Lower average values were obtained its the present study in general; this is due to the recent sampling procedure iti which very weals to strong samples were taken to reduce the bias in sample selection. This procedure resulted in large standard deviations and coefficients of variation for the recent testing. Except for doubt in the E Seam floor where only two tests were made, present testing co[tfirmed previous results. Table 3.4.A.10 is more relevant and compares uniaxial compressive stie[tgtlts according to rock types. As shown by the roof fall experience its the F Seam, carbonaceous shales are much weaker than other beds. Interbeds also tend to be weaker. T}ttts, a comparison of stability may be made by evalttatictg the thickness and position o£ carbonaceous shales bed. in relation to the top of the coal. A fact whi.clt may aid stability in some areas of the B Seam is that the seam thickness may allow top coal to be left in some areas to support carbonaceous shale beds. Table 3.4.A.11 summarizes the range and average of all uniaxial and tensile strength testing and elastic constants obtained from the • compressive tests. The rattges are very wide in most cases acrd the averages are relatively similar between the seams. Of course this restclt does not imply identical grouted conditions between the seams because of differences in bed thickness, rock type, geologic features, a[td stress. It shows, however, that identical average mechanical property values between the seams may be used in the analysis when evaluating stress distributions. A limited amount of data is available on c~~al. strengths. Its this study, triaxial. testing was performed on five core samples from the B Seam and one from the F Seam. Old and new data indicated nearly identical coal strengths between the seams. Table 3.4.A.12 summarizes uniaxial compressive strength data from four seams a[td Figure 3.4.A.4 summarizes triaxial strength data from t}[ree seams. Presently, no triaxial data is available for the E seam. The results indicate close strettgttt behavior wit}ti[t the range of lateral stresses expected at West El)c. Slake durability tests were performed on roof and floor samples of the E and B seams. This type of test indicates the degree of rock disintegration whets it is its contact with moisture. The results are shown in Table 3.4.A.13 and range from low to high durability, probably mostly dice to the clay content variability of the shales. Thus, slaking in some areas of the E and B Seams should be expected, but probably to a less extent than in the F Seam. The reason for this • difference is dtte to the smaller amounts of water and moisture expected underneath the stream valleys (increased depth) and probably ~ lower amounts of clays in the shales.