1987-12-01_PERMIT FILE - C1981017 (103)

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commended appropriate construction procedures for the rock waste disposal facility. Although no gradation curve is available for the material , it is evident that the rock waste comprises a fairly good quali- ty rockfill with a minor amount of fines. According to the Uni- fied Classification System, it could probably be classified as a silty gravel (GM) or possibly as a poorly graded gravel-sand mix- ture with little fines (GP) . Lincoln DeVore performed Standard Proctor Tests (ASTM D- 698) . Their tests indicated a maximum density of 131.2 pcf. They also performed triaxial tests with the material which was re- molded at approximately 90 % of the maximum density. The tests indicated a friction angle = 29 degrees and a cohesion C = 1,296 psf. As the large fragments of rock were removed for test- ing , the results are very conservative . Lincoln DeVore performed stability analyses of a slope not exceeding 60 feet in height. The analyzed slope had two ten foot wide benches included. The slope between the benches was 2 (H) : 1 (V). - Other, flatter slopes were analyzed as well. As can be ex- pected , the factors of safety were reasonably high. A minimum factor of safety was found to be equal to 3.5. Based on the results of these analyses , Lincoln DeVore recommended to accept the analyzed slope configuration; they re- commended to compact the outer shell of the waste pile to 90 % of Maximum Proctor Density. They also recommended to place the waste in lifts not to exceed 12 inches loose thickness. Material located beyond the outer shell of the pile was recommended to be spread in lifts not exceeding two feet in thickness. No com- paction was recommended for this zone of the facility. Mid-Continent proposed in their Permit Application trucking of the tunnel spoil material to the disposal area and spreading and compacting it according to these recommendations. 4. 0 FIELD AND LABORATORY INVESTIGATION t 4. 1 COAL REFUSE DISPOSAL FACILITY The coal refuse disposal facility was visited on April 18, L 1984. The purpose of our visit was to visually inspect the ex- isting coal refuse facility, to verify the construction methods, i to perform in-place moisture and density testing, and to obtain L samples for the determination of moisture and density relation- ship. Testing was performed by Chen & Associates Laboratory in 4 Glenwood Springs. t_ 16 GEO-HYDRO CONSULTING,INC.