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• Pillar stress was calculated using a pseudo-three-dimensional boundary element <br />technique that accounts for the variability in the overburden realistically. The stability of <br />the overburden rocks was studied in more detail using a three-dimensional finite- <br />difference code and effective stresses that take pore pressure into account. <br />The field program is described in section 2 and the geotechnical framework for BRL <br />properties is reviewed in section 3. Section 3 also includes an evaluation of the stress <br />field and representation of rock mass quality for the entire overburden. A methodology <br />suggested by NIOSH is used in section 4 to address mains orientation and pillar stability. <br />Because of variations in the overburden, a boundary-element method was used for the <br />calculation of pillar factor of safety. Section 5 presents the results of three-dimensional <br />finite-difference analyses in which the stability of the overburden at the corridor is <br />quantified. Conclusions and recommendations are presented in section 6. <br />U <br />0 <br />Maleki Technologies, Inc. Page 3