Date of Award
Master of Science (MS)
Data on subsurface conditions obtained prior to strip mining is useful in planning effective mining and reclamation procedures as well as predicting the subsurface characteristics after reclamation. The redistribution of the overburden sediments is less predictable, however.
Through field observations, the major mining factors controlling subsurface structure and overburden sediment redistribution were determined. These include the geometry of the coal body, pit sequence, pit curvature, overburden thickness and managerial input. At a given location, however, the detailed structures and distribution of sediment types within a waste bank were observed to depend upon the dragline cutting pattern, distance between dragline positions, the previous mining activity adjacent the dragline position, mass wasting, overburden stratigraphic sequence, breaking characteristics of the overburden sediments, dragline bucket motion and operator variability.
Waste banks were classified into morphological types which vary from small conical banks in thinner overburden areas to large level-crested banks in thicker overburden areas. Within a waste bank, the sediments were segregated to a varying but somewhat predictable degree into beds that lie at an angle of about 38°. The sequence of sediment types deposited within the waste bank depended primarily upon the sequence of sediments in the overburden and the bucket motion. Secondary sorting occurred when the large clasts of consolidated sediments rolled to the base of the waste bank. Patterns of sediment distribution along waste bank slopes have been empirically derived.
The contouring processes that subsequently rearranged the sediments of the upper part of the waste banks were classified. It was observed that few concentrations of large clasts were produced in this phase except when frozen banks were contoured. By whatever processes they were produced, concentrations of large clasts have been observed to eventually cause surface collapse. When beds of waste banks are truncated in the contouring process, irregular zones of sediments with phytotoxic substances may be exposed.
The production of potential aquifers during the stripping and contouring processes were observed. These potential aquifers include inter- and subbank blocky zones and beds of permeable sediments within the lower parts of waste banks. Flow will probably concentrate within the area between waste banks. Groundwater recharge will probably occur through the highwall of the initial pit, with minor recharge occurring through perched aquifers cut by the final pit.
Winczewski, Laramie M., "Western North Dakota lignite strip mining processes and resulting subsurface characteristics" (1977). Theses and Dissertations. 328.