At the joint development of the deposit by open and underground methods, the deformation of the underground mine shaft may occur. Its size and direction significantly depend on the procedure of conducting mining operations in the open pit in comparison with the works on the shaft sinking. In this case, the maximum permissible deformations of the shaft are determined by its design and set in the relevant regulatory documents. The article is mainly devoted to the methodology for assessment of mutual influence of the open-cast workings and the vertical shaft.
Usually, the permissible distance from the pit edge to the underground mine shaft is estimated by the position in the massif of the «fault potential surface» with a set normative coefficient of the margin stability. Such a surface can always be built at any stage of the development of the open pit mined space considering the underground work among other things. In the case, the set maximum depth of the open pit, when the open pit finishes its operation, the intersection of the «fault surface» with the day surface determines the certain curve on the latter. This limits the area around the open pit, in which the location of the shafts is considered unacceptable. Although in this case the safety margin of the pit walls can have the significant value equal to the normative one or greater, the deformation of the shafts may become unacceptable for their functioning.
Disadvantage of this approach is the fact that the «radius» of this zone significantly depends on the used method of building the «fault surface», which is repeatedly shown by the calculations. The approach proposed in the article is oriented to considering the peculiarities of deformation of the entire massif in the vicinity of the open pit, taking into account its possible real collapse as the limit state is reached, when the large massif deformations are actually realized.
In considering the deformation processes in the massif, in particular in the vicinity of the shaft, the order of the workings formation is of great importance. In this case, the shaft can only be deformed by those works on the open pit deepening that are performed after creation of the shaft or any part of it. If the shaft is sinking after deepening the open pit, then the mined-out space of the open pit in no way affects the deformation of the shaft, since it is being sinked already in the deformed massif.
If the open works and the shaft sinking are simultaneous, then the solution to the problem is divided into a series of consecutive steps, each of which considers either some element of the open work or the shaft deepening. Final decision is obtained as a result of summing up the decisions at each step.