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William A. Bear <br />Page 3 of 4 <br />August 15, 2014 <br />120.0 <br />w, 115.0 <br />U <br />110.0 <br />.7 105.0 <br />G 100.0 <br />G 95.0 <br />E <br />90.0 <br />E <br />85.0 <br />80.0 <br />75.0 <br />Coal Mine Waste - Max Dry Density <br />Comparisons <br />0 100 200 300 400 500 <br />Chronological Test Sequence <br />♦ BGI MDDs <br />--W-MDD - Avg <br />—*--MDD - Max <br />X MDD - Min <br />--)I -HBET 14 -0195 <br />—*--HBET 14 -0373 <br />+HBET 14 -0375 <br />For the 2nd Qtr 2014, compaction testing was performed by HBET. The MDD values <br />to which the field densities (DD) are compared are not unique to each field test. <br />Rather, it appears that HBET may have established (at least) three separate <br />"Proctor" Curves in the laboratory, to which the Gob at a particular spot can be <br />compared. This technique, though different from that employed by Buckhorn, is <br />commonly used in highway construction projects. Samples of soil are collected <br />which span the full range of materials that are likely to be encountered during the <br />project (clayey, silty, sandy, rocky, or combinations of these). A suite of Curves is <br />created, and the field technician then chooses the appropriate Curve to be used for <br />comparison for the material that is being compacted at a given time. <br />The three HBET MDD reference values are also plotted in the graph above. As we <br />can see, the first two MDDs (at 104.0 and 106.0 pcf) are somewhat higher than the <br />average observed to date, but they are well within in the range that we might expect <br />to see. The third MDD, however, at 79.5 pcf, is lower than even the Minimum result <br />obtained by Buckhorn over the course of 2 -plus years. In the 2nd Qtr report, this <br />third curve was referenced on four separate tests, three of which "passed" with <br />densities >100 %. <br />a. The Division requests that BRL provide a description of the process now being <br />used to evaluate compaction of the Coal Mine Waste at the Bowie No. 2 Mine. <br />Please include copies of any Proctor curves that have been generated for Gob <br />at the site, together with any differentiating factors for each Curve that the <br />tester will be using so the proper Curve is selected for reference with each test. <br />