Laserfiche WebLink
Mining Methods and Slope Stability Evaluation for Expanded Development of the Walstrum Aggregate Quarry <br /> Excavations that must be extended southward can be made by gradually extending the benches of <br /> eastward-mined walls as shown in green in Figure 4.2. At the southern quarry limits of these east- <br /> mined benches, blastholes can be progressively shortened to create a final slope with an angle <br /> matching the dip the strata. <br /> 4.2 Bench Height, Final Pit Slopes and Vertical Mining Direction <br /> In the existing MLRB (Mined Land Reclamation Board) permit and in the expansion plan, final <br /> quarry walls on the north side of the quarry will be sloped 3H:1 V or 18.4 degrees. Final pit walls <br /> at the eastern boundary of the quarry, in the planned expansion area will be created with stair- <br /> stepped 40-foot mining cuts and 40-foot horizontal catch benches to create an overall 1:1 slope at <br /> 45 degrees. The recent survey of rock conditions in the Walstrum quarry revealed that existing <br /> west-facing walls at the east side of the pit, oriented about 53 degrees from the strike of the <br /> gneiss foliation are stable. To further ensure the stability of the final walls, other controls designed <br /> to limit the impacts of blasting and water effects on wall-stability are also recommended in this <br /> report. An isometric drawing showing the shape and rock-structure conditions of the final walls at <br /> the eastern boundary of the planned expansion area is shown in Figure 4.3.When blasting next to <br /> final pit walls, using air-decked charges in holes drilled along the final slope will minimize rock <br /> damage. Details on recommended air-deck blasting methods are described in Section 4.4. Loose <br /> rock should be scaled from final rock faces and where needed, rock bolts of appropriate length <br /> and strength should be added to spot locations where features indicate potential wedge or local <br /> block failures might occur at some future time. It is much easier to implement these measures <br /> while the rock face can be accessed from equipment working on the shot rock while excavating <br /> the bench. <br /> Wherever possible, new mining benches should be developed to facilitate mining highest benches <br /> ahead of lower benches. By so doing, larger horizontal offsets can be maintained between <br /> benches, which lessens the overall pit-slope-angle. Moreover, exposing a series of relatively short <br /> vertical rock faces versus a relatively steep wall will reduce the risk of wall failures. <br /> If the measures recommended in this report are followed, the overall stability of final pit walls in <br /> the eastern side of the Walstrum pit should be stable. <br /> REVEY Associates, Inc. Page 9 of 14 October,2001 <br />