In the development of ore deposits and stratum-shaped thick deposits in most cases are used chamber systems with multi-stage ore excavation, resulting in the formation of unconfined cavities of significant volumes ...

At present, considerable experience of experimental and theoretical studies on stress distribution around excavations of different cross-sectional shape has been accumulated. Most of these studies have been carried out in relation to workings with a smooth contour, however, it is known that the drilling and blasting method of sinking produces an uneven contour of the excavation. Technological irregularities formed in this process, and also occurring in some cases rock dumps, cause redistribution of stresses with the formation of zones of increased concentration. In full-scale conditions it is difficult to determine the value of stress concentration in these zones. Therefore, studies are usually carried out on models.

The stability of the rock massif in a group of mine workings depends to a great extent on their mutual location and the ratio of cross-sectional dimensions, as well as on the nature of the application of loads. Below we consider the results of the study of the stressed state of rocks during two vertical workings at the Tekeli mine, where the shaft with a diameter of 6.7 m and the ore spout with a diameter of 3.4 m were passed at a distance between their axes of 15 m to the depth of X horizon (572 m). In unstable rocks the mutual influence of these workings on each other leads to significant deformations of rocks and their dumps.

When developing powerful steeply falling formations with the division of the floor into sub-floors (for example, at hydro-mines), effective means of supporting the sub-floor drifts are required. The support should provide reliable stability of drifts and ease of its installation - conditions for high rates of drifting by shearers or hydro-monitors. The type of such support depends primarily on the amount of rock pressure, which is the result of the distribution of stresses in the rock mass around the excavation.

As is known, ductile strength is characterized by the shear resistance of a material Sshf, and brittle strength is characterized by the breakaway resistance of a material Sref. Under a complex stress state, the ductile and brittle strength criteria of a material are functions of all three true stresses S1, S2 and S3. If the functions from S1, S2, S3, expressing shear and tear resistance, are chosen correctly, then the mentioned strength criteria for a given material and its physical state before loading will be constant, independent of the type of stress state ...

Yield strengths in tension and compression are very important strength characteristics of plastically deformable materials with both large and very small plasticity. These characteristics of mechanical properties are necessary for strength calculations in bending, torsion and other types of complex stress states of structural elements and machines, the material of which resists tension and compression unequally.

The mathematical theory of plasticity is based on the law of the existence of a generalized function of the mechanical state of a material at constant temperature and strain rate. The essence of this law is reduced to the recognition for each material of a generalized, independent of the type of stress state, curve of plastic flow in certain coordinates. The conditions of plasticity and strength theory express this law by various equations characterizing the hardening of the material during its plastic deformation.The influence of normal stresses on the resistance of a material to deformation is quite obvious, since normal stresses in shear planes cause frictional forces that facilitate or impede the plastic flow of the material. In order to at least approximate the strength of a material under a complex stress state, it is necessary to perform at least two comparative tests for two types of stress states: tension-compression, tension-torsion or, in extreme cases, tension-cutting. The initial tests should be as simple and reliable as possible.