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spoil bank[′spȯil ‚baŋk]
an accumulation on the surface of a mine of waste rocks or substandard minerals removed in working deposits; a heap of tailings from ore-washing plants or sludge from metallurgical plants. In open-pit mining spoil banks are divided according to their location into inner banks (in the excavated parts of quarries) and outer banks (accumulated outside quarries). Depending on the topography, spoil banks are called lowland or highland banks, and depending on the number of layers, they are known as single-stage or multistage spoil banks. They are also divided according to the machine used into excavator (shovel), plow, chain-and-bucket, bulldozer, hydraulic, or combined spoil banks.
The construction of a spoil bank begins with the making of an initial heap using draglines, power shovels, chain-and-bucket excavators, bulldozers, or scrapers. During the mining operation the spoil is accumulated in layers. Spoil banks may be parallel, fan-shaped, curvilinear, or circular; parallel or curvilinear displacement of the front is common. The development of the front from its initial position may be one- or two-sided. The basic geometric parameters of spoil banks are area, height, and slope. Much importance is attached to the stability of spoil slopes, which is determined by the geological engineering conditions and the technology of making spoil banks, the geological structure of the spoil bank and the foundation (the lithological composition, structure, and texture of the rocks and the hypsometry of the foundation surface), the hydrophysical and mechanical properties of the spoil rocks, and the technique used in making the spoil bank.
The height of spoil banks consisting of soft rocks and rocks of medium hardness usually does not exceed 30 m. Spoil banks composed of hard rocks may reach 60 m, and on slopes and in gorges they may be as high as 300 m. In working deposits by underground methods, the spoil banks of waste rocks on the surface are known in Russian as terrikonniki. After mining operations have ended, areas occupied by spoil banks are reclaimed.
B. K. ALEKSANDROV and B. A. SIMKIN