Operating conditions of earth dams on undermined territories

Abstract

In connection with intense underground mining operations, not only industrial and civil buildings and structures, railroads, and pipelines but hydraulic structures as well --earth dams, reservoirs, and ash and sludge storage ponds --fall into the zone of influence of undermining.According to the existing standards all undermined structures should be protected from the harmful effect of undermining. To provide reliable operation of structures it is necessary to know the permissible values of the parameters of deformation of the foundation and in the case of exceeding the permissible deformations, to take various steps to eliminate possible failure of the structure.Failures of earth dams, as shown by the considerable experience of operating these structures, are associated with considerable material damage in connection with emptying the reservoir and flooding of nearby territories and with loss of life, and failures of dams of sludge storage ponds can lead to pollution of the environment [1][2][3]. it is impossible to forbid undermining of earth dams and dikes of reservoirs and ash and sludge storage ponds, since in this case it will be required to leave untouched large mineral resources located under them. This problem is completely new. It is of interest to examine the conditions under which hydraulic structures fail.Underground mining has one common important characteristic consisting of as a result of extracting minerals, cavities are formed in the rock mass which disturb the equilibrium of the surrounding rocks. This disturbance leads to their subsidence starting directly from the adjacent lower beds with subsequent development right up to the surface, which also experiences vertical and horizontal displacements and deformations. In this case the part of the surface subjected to the effect of mining operations is usually called the subsidence trough~ In the general case points of the surface and underlying layers have both vertical absolute movements (subsidences) and horizontal displacements (offsets) directed from the margins of the trough toward its center. The subsidence trough is usually also characterized by relative quantities, whereupon by horizontal elongation--compression strains e is meant the same as in hydraulic engineering, i.e., Sx = Al/l (Al is the increment (shortening) of the investigated area with length l). Nonuniform subsidences are denoted in terms of the slope i and curvature K = I/R = Ai/lav (Ai is the difference of slopes of two adjacent areas; lay is the average length of these same two areas). The vertical sections of the trough passing through points with maximum subsidences of the surface are called its principal sections. Central, flat, and marginal parts of the trough are distinguished according to the character of the distribution of the principal parameters. The character and regularity of the distribution of the principal parameters of subsidences along the length of the marginal part of the trough L were established on the basis of long-term on-site instrumental observations...