In present work the systematic investigations on the mechanical characteristics of rocks under tree-dimensionally stressed state conditions, close to those, acting within the massif, are described. The program on mechanical tests of rocks is carried out, depending upon the calculated qualitative changes of principal stresses and three-dimensionally stressed states near the mine workings. The developed energy criterion of rock strength includes the deformation forces, acting under the deformation conditions, the shape and volume changing, their limiting values and the Nadai-Laudet parameter, taking into account three-dimensionally stressed state types.
The rock and rock massives loading conditions have a pronounced dimensional character. The relations between three principal stresses, characterizing mechanical state of rock massif near the mine workings are changed naturally. It defines the corresponding massif deformations and failure. The investigating the complex rock massif deformation and failure processes would be more successful under the natural conditions. However, the single tests only are possible in this case because of substantial production problems. The thorough preparation work for mine tests includes the necessary laboratory and analytical study. In present work the systematic investigations on the mechanical characteristics of rocks under the three-dimensionally stressed state conditions, close to that, acting within the massif, are described. this study allows to reveal the most characteristic features of geo-mechanical processes, proceeding Within the massif and to determine the main process parameters changing trends.
As for the gentle sloping rock bed in front of the face, all three principal stresses, acting in geo-mechanical processes, which proceed in the above mentioned zone within mine workings, are compressive, and three-dimensionally stressed state in different massif areas varies from summarized compression to summarized tension (Norel 1983). Three principal stresses, defining the three-dimensionally stressed state within the massif, are varied qualitatively as follows. When approaching the face, the maximum compressive stress, directed vertically relative to the working plane and defined as б3, increases from the vertical compressive stress value within unmined massif zone up to the peak value, which equals in the maximum compressive stress zone (where Kk is the concentration index) and then falls down to the strength index value at the face edge. The intermediate compressive stress, directed over the length of the face and defined as б1, varies from λp3 within unmined massif zone to the 1/2 (б1+ б3) value in maximum compressive stresses.
The program on mechanical tests of rocks is carried out depending upon the calculated qualitative changes of principal stresses and three-dimensionally stressed states near the mine workings. Before analyzing the test results, some statements on deformed media mechanics. being used in this work (Nodai 1969) should be considered because there is always the algebraic inquality б1≥б2≥б3 for three triaxial principal stresses. In this case the compressive stresses and deformations are negative; tensile stresses.
Tensor decomposition for three main types of three-dimensionally stressed states has allowed the more clear understanding of physical foundations of the summarized compression.
