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Asphalt Paving Co. <br /> February 10. 2015 <br /> Page 2of2 <br /> The effective friction angle and cohesion for the average basalt joint was arrived at by <br /> examining all of the test results performed on both the core basalt and rim basalt as well as by <br /> back analysis of an existing slip on site. <br /> General observations indicated no large-scale slope failures at the mine site. The dip of a <br /> medium-sized slip located in the north part of the mine along the west wall was calculated to be <br /> approximately 33 degrees through analysis of apparent dip based on photographs and field <br /> notes. Further analysis was performed using the limit equilibrium program SLOPE/W by GEO- <br /> SLOPE International to estimate the joint's properties based on a predefined failure plane <br /> consistent with those observed in the field. This analysis gave an approximate friction angle of <br /> 33 degrees for the joint. <br /> Only a few local slips along dip-slope joint orientations were observed; based on conversations <br /> with APC we understand these localized slips occurred as a direct result from blasting at that <br /> location. Back analysis of an actual measured observation has been included in evaluation of <br /> material properties; inclusion into the modeling adds some conservativism to the model due to <br /> the mechanism causing release. Brierley's evaluation concludes similar surficial slips do not <br /> pose a significant slope stability hazard and they can likely be mitigated during the ongoing <br /> mining process. <br /> Closure <br /> We appreciate the opportunity to work with you on this project. If we can be of further <br /> assistance, or if you have any questions, please contact our office. <br /> Sincerely, <br /> BRIERLEY ASSOC)ATES <br /> LeO(cc B(ck, P , P Steve Kuehr, PE <br /> Associate ` Principal <br /> Attachments: Appendix A— Laboratory Results <br /> BRIERLEY <br /> ASSOCIATES <br /> Creating Spare Underground <br />