GEOLOGIC AND ENGINEERING ASPECTS CONCERNING SLOPE STABILITY OF SURFACE COAL MINE SPOILS

CELESTINE OBIALO OKAGBUE, Purdue University

Abstract

Three spoil slope slides, two in the Appalachian Plateau region (Pennsylvania and West Virginia) and the third in the Interior Coal Province (Southwestern Indiana) were studied to determine types and causes of slope instability. The two slides in the Appalachian plateau region were associated with contour strip mining, whereas the Indiana site was associated with areal strip mining. The objectives were: (1) To examine in geological detail the nature of the spoil piles under study and the materials from which they were derived. (2) To identify types of spoil stability problems and the factors that contribute to these problems. (3) To determine the relationships if any between the overburden and foundation materials, their properties and the nature of failure. (4) To provide guidelines which suggest locations with a high probability for slope instability during mining and supply recommended procedures to reduce these effects. Geologic, geomorphologic, hydrologic, material and man-induced factors were evaluated to determine their influences on the slides. Stability analyses were performed to determine failure modes of the spoil slope in each site and influence of input parameters on the stability of the slopes. Conclusions: (1) That the spoil stability problems in the Appalachian region may have a primary cause--the presence of expandable clays. These clays absorb much water and swell, thus exerting an upward pressure that may reduce shear resistance within the soil or rock that contains them. (2) That water was usually the activating agent for the slide activity. (3) That the interaction of geomorphologic, hydrologic and man-induced factors are collectively responsible for the entry and accumulation of water within the sliding spoil. (4) That the spoil slide in Pennsylvania was basically an outslope foundation failure whereas that in West Virginia was a spoil outslope failure. (5) That the spoil slope angle presently adopted in the southern Indiana mine site will lead to occasional slope failures in areas where the unconsolidated overburden is very thick and consists essentially of low strength clay. Corrective measures are suggested to improve stability of spoil piles in the areas. Based on the study findings a site evaluation chart is proposed to aid mine operators in identifying problem areas.

Degree

Ph.D.

Subject Area

Geology

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