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<br />be acceptable. Additionally, cutting the bench back slightly will have the effect that the <br />rock exposed in the highwalls and benches will be more competent because it is further <br />back from the original quarry walls, which likely had a higher degree of disturbance from <br />the original mining without controlled blasting techniques and from the previous failure. <br />A system of survey monuments is planned to be installed to monitor the upper benches of <br />the slope in accordance with Mine Plan Amendment No. 3. <br />North Ouarry. Results of the geologic mapping at the northeast area of the North Quarry <br />revealed the following general conditions: <br />The parent rock material within 20 to 50 ft of the original ground surface is highly <br />weathered. The degree of weathering decreases with depth. Additionally, zones of <br />brecciated rock were observed. Within the weathered zone, the rock is estimated to <br />have an unconfined strength less than 15,000 psi and in some highly-weathered and <br />brecciated zones, less than 2,000 psi. Weathering is more pronounced in the schist <br />zones than in the granite and gneiss zones of the formation. <br />2. The primary joint set is along foliation of the gneiss and schist roclt. It strikes <br />N75°W which is approximately parallel with the ultimate orientation of the north <br />wall, and dips 60 degrees south which is approximately perpendicular [o and out of <br />the north wall slope. Folding and shearing has created a series of small syncline and <br />anticlines from approximately 20 to 100 ft across. As a result of these anomalies, the <br />strike of the foliation joints varies by 45 degrees either direction from the predomi- <br />nant strike direction and the dip typically varies by 20 degrees or rnore. Joint <br />spacings typically range from several inches to approximately three ft. Joint surfaces <br />vary greatly from fresh to highly-weathered. Slick, weathered schist zones are <br />frequent. <br />3. At least two secondary joint sets are present, often orthogonal witlr the primary joint <br />set. These secondary joints typically occur at intervals of one to five ft. In general, <br />secondary joint surfaces are fresher and less-weathered than the foliation joints and do <br />not typically exhibit the smooth schist or mica surfaces. <br />4. At the base of the presently exposed north slope, a large planar joint srtrface is <br />exposed as a result of the wedge of overlying rock sliding on the join[. This surface <br />is approximately 100-ft long and 60-k high, it strikes N75°W approximately parallel <br />with the slope, and dips 55 south which is out of the slope. On a large scale, the <br />surface is planar but local variations create an undulating surface with variations in <br />strike and dip by 20 degrees. <br />Based on [he conditions observed with the present exposures, the rock mass at the <br />northeast area of [he North Quarry is tentatively classified as "poor" in terms of the <br />previously-established baseline conditions. This classification is based primarily on the <br />adverse orientation of the primary joint set along foliation which dip out of the slope. <br />Additionally, the rock mass within the weathered zone is classified as "poor" based <br />primarily on [he low strength of the parent rock material. The large joint feature noted <br />above is a direct result of this situation. In addition to this situation, other localized areas <br /> <br />