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L Mine Bench Stabilization <br />JI November 9, 1984 <br />Pdg€ 2 <br />i 5. Inflow of water in the excavation immediately above the <br />•1 surface between approximate station 3 + 4 to 300. Water <br />was being removed utilizing sump pump operations as fill <br />proceeded. <br />6. Large rock fill material had been stockpiled beyond the toe <br />of the slope to be utilized as a rock fill material. This <br />material was observed to be sufficiently large and durable <br />for use as rock fill material as provided in the plans. <br />7. Tension cracks were observed along the edge of the bench at <br />the top of the surface and at various intervals throughout <br />the slope. Movement was observed while on-site during <br />inspections. <br />8. Initial fill operations between approximate station 3 + 40 <br />and 3 + 20 began with placement of the material consisting <br />of a mixture of bench fill material and 8-inch minus rip- <br />rap material. This rip-rap material was brought on-site <br />for use in surface erosion areas, however, it was felt that <br />it was sufficiently coarse to be utilized as a stabilizing <br />base at the bottom of the excavation. This mixture was <br />placed in an initial lift to provide a stabilized base <br />~~ above the rock surface in saturated areas. This material <br />provided a rock to rock contact necessary in order to <br />prevent buildup of pour pressures during fill operations. <br />9. Seepage and wet areas at the base of the slide were <br />+ observed to exist. This condition provides further <br />q evidence that no further excavation of this loose material <br />-1 should be conducted until fill placement operations reach <br />1 that elevation. <br />Photographs of all the observed conditions were taken for <br />documentation and will be available upon request at our office. <br />RECOMMENDATIONS <br />In order to provide consistent construction operations, <br />efficiency in doing work and to maintain the existing bench, the <br />following recommendations are provided for assistance to the <br />construction operations. <br />1. Excavation in the toe area of the slope, where penetration <br />of the bedrock is required, should be a minimum of 2 feet <br />into the claystone material. <br />2. Improved efficiency of the fill operations using scrapers, <br />after the toe area has been stabilized, could conceivably <br />increase the volume of fill material placed and thereby, <br />expediting the completion of the bench. <br />