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

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In order to obtain results on the refuse compaction not only at the surface but at certain depths, Mid-Continent arranged for the excavation of several trenches, where testing could be per- formed. According to the visual observation, it is evident that the coal refuse has been placed in horizontal lifts as specified in the Permit Application. The waste pile slopes have not yet been constructed according to the specifications. It was evident that ' some coal waste material was dumped over the crest of the exist- ing facility slopes. As the slopes are still steeper than the final design slopes, and because of probably high moisture content of the coal refuse at the present climatic conditions, numerous slides having a character of mudslides developed on the sides of the disposal facility. A probable reason for the de- velopment of such mudslides is the high moisture content of the material , caused very probably by excessive snowfall of this late spring season. It is evident that these surficial slumps have to be treated in the dear future so that the pile construction complies with the s: ecifications. A total of nine in situ density measurements have been taken on or below the surface of the coal refuse disposal facility. The results of the testing are presented in the Appendix of this report. The tests were performed by using a nuclear density device (in seven cases) and the sand cone method (in two cases) . The depths of the performed tests varied between 0 to 8 feet below the surface of the pile. Unfortunately, the moisture and density testing results performed by the nuclear density device are not reliable because of the high coal content of the refuse. Two results of in situ density testing using the sand cone method proved, however, that the waste has been compacted practically to the maximum dry density, as estimated by laboratory testing. In both cases, densities over 105 pcf have been measured. Maximum dry densities on the material from the close vicinity of the in situ tests indicated a maximum dry density of 99.8 and 106.6 pcf. It is evident from these results that the coal refuse has been compacted to acceptable values. The inspection of the waste pile indicates several wet spots on the surface of the pile, probably caused by inadequate removal F of snow on the surface . L Favorable results of in situ density testing indicate that the results of triaxial testing performed by Morrison-Knudsen can ibe fully applied. Triaxial testing by Morrison-Knudsen was per- i __ formed with conservative densities of only 80 pcf. r - f L: 17