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Dickerson Pit Wall Stability 2 July 31, 2000 ordinary soil slope. If the rock classifies as R2, moderately weak rock, further testing to determine the sheaz strength of the rock would be required to decide if it could be benched or terraced for reclamation. Rock that classifies at R3 or higher is not likely to fail through the intact rock, and only the fracture orientations would be of concern. 3. Daylighted fracture or joint sets aze potentially subject to plane shear sliding failure whenever the fracture is flatter than the slope angle and steeper than the angle of surface friction along the fracture. The resistance to sliding along the natural joints must be exceeded by the down dip thrust of the potential sliding block of rock for a failure to occur. Resistance to sliding along joints is provided by friction created by the weight of the rock above the joint, the roughness and irregulazity of the joint surfaces, whether the joint is open or closed, and if a mineral infilling heals the joint. Other factors that influence the degree of resistance to sliding aze the dip angle, presence or absence of water, if there is a clayey or slickenside fracture surface, and the presence, extent, and strength of intact rock bridges across the fracture surface. The personnel assigned to measure and map the fractures must make observations of these features and log them in the field notes to make a complete evaluation of the stability of the proposed highwall configuration. The field measurements and observations may be used to estimate the proportion of broken and intact rock along potential joint failure surfaces. Observations and testing may be used to estimate the strength of intact rock bridges if they aze present along adverse fracture orientations. 4. If adverse fracture orientations are present at the Dickerson Pit, it may be necessary to conduct a physical testing program to determine if the proposed pit wail conftguration wiil be stable in the long term. A testing program would typically include uniaxial and triaxial testing of representative samples of the different types of rock exposed in the quarry, as. well as direct sheaz testing of fracture surfaces to estimate the degree of shearing resistance available along the fractures. Shearing resistance along adverse fracture orientations can be adjusted to include the influence of fracture irregulazity and intact rock bridges, and can be applied in limiting equilibrium slope sta t try an yses. e e a ce _ of gravity on a rock mass above a fracture surface) to the force resisting movement, which aze the frictional forces. A ratio of these forces yields the safety factor for the pit wall. Any safety factor above one, if the inputs to the ratio are accurate, indicates that the pit wall will be safe. 5. As continued quarrying encroaches upon the final pit wall location, it is important that intact rock bridges along any adverse fracture orientations aze preserved to ensure long term stability. Production blasting practices may potentially damage or destroy the rock bridges. If adverse fracture orientations are present at the Dickerson Pit, the Operator may be required to commit to a perimeter blasting plan. This plan would allow the Operator to employ standard production blasting practices in the majority of quarry operations. As the final pit configuration is approached, alternate blasting practices could be implemented to protect the integrity of rock bridges. Such practices include cushion blasting, precision blasting, smoothblasting, and presplit blasting.