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25 <br />about the same strength as the <br />than the Upper Wheeler roof. <br />strength would be appropriate <br />appears moderate, but there is <br />ing. <br />interburden rocks, but are weaker <br />A description of low to moderate <br />for these rocks. Slaking potential <br />little or no potential for swell- <br />Sandstones, siltstones and claystones. The siltstones are <br />rated as strongest, followed in order by the sandstones and clay- <br />stones. In general, the siltstones would be rated as moderate <br />to high strength while the sandstones would be rated as moderate <br />in strength. The claystones would be rated as low to moderate <br />strength. The siltstones have a high slaking potential while <br />the claystones have but a moderate potential. No slaking potential <br />should be expected in the sandstones and no swelling potential <br />should be expected in any rock type. <br />Overburden Rock Ceotechnical Characteristics. The geotech- <br />nical characteristics of Drill Hole 3.75 were fully investigated <br />relative to recovery, RQD and point load strength. These character- <br />istics were recorded and measured for all drill core from the <br />hole collar to a total depth of 1601 feet. The results have been <br />plotted as a function of hole depth and are presented in Figure 2. <br />Such a series of logs may be used to assess the overburden stiff- <br />ness for subsidence studies. <br />NOMINAL DESIGN PARAMETERS <br />Based on the geotechnical logging and testing, a set of pre- <br />liminary nominal design values has been developed. A summary of <br />these physical properties is presented in Table XII. <br />SEEGMILLER INTERNATIONAL <br /> <br />