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others 1992). These measurements have shown that both premining vertical and <br />horizontal stress can be elevated under stream valleys. The expected horizontal stress <br />field in the rock mass at Terror Creek is estimated as follows: <br />P= Maximum principal horizontal stress= 1520 psi <br />Q= Minimum principal horizontal stress= 420 psi <br />3.3 Mechanical Properties <br />Mechanical and strength properties for coal- measure rocks and the overburden are <br />reviewed here for addressing rock mass strength characteristics near the corridor. MTI <br />designed the testing program to ensure adequate characterization of both strength and <br />deformation properties of rocks. <br />Rock mechanics tests were completed at selected intervals along the three geotechnical <br />coreholes. The purpose of testing was to determine: <br />• Uniaxial compressive strength <br />• Young's modulus and Poisson's ratio <br />• Point -load strength along both core vertical axis and horizontal directions <br />(diametrically) <br />In addition, an attempt was made to obtain confined (triaxial) strength for coal samples <br />for calculation of angle of internal friction and cohesion. These efforts however were <br />mostly unsuccessful because of the cleated nature of the Upper B Seam at this location. <br />3.3.1 Overburden properties <br />Figure 4 presents histogram frequency diagrams for the uniaxial compressive strength <br />and Young's modulus. Data statistics are also provided for the entire data base, including <br />laboratory test results from three holes. Using an engineering classification of intact rock <br />(Deere and Miller, 1966, table 2), Terror Creek core is classified as having medium <br />strength, and on the average, a medium modulus ratio. The modulus ratio is obtained by <br />dividing Young's modulus by uniaxial compressive strength. <br />El <br />• <br />Maleki Technologies, Inc. Page 13 <br />