Investigation of influence of stress state parameters of fault zones on peculiarities of their mechanical response under shear loading

The paper is devoted to theoretical investigation of the influence of stress state parameters of healed fault zones fragments on the characteristics of their mechanical response under shear deformation in the conditions of nonequiaxial compression. Investigation was based on computer-aided simulation by the movable cellular automaton method. Dimensionless parameter, named the degree of nonequiaxiality of compression was used as the basic parameter of stress state of the medium. This parameter characterizes the ratio of lateral and normal stresses in the plane of deformation. The main objective of the paper was to analyze the dependences of the shear strength, ultimate shear strain and value of volume changing (dilatancy) on the degree of compression nonequiaxiality at the initial stage of activization of the fault zone fragment. It is shown that the degree of compression nonequiaxiality of the medium is an important factor affecting the conditions under which healed fault zone could be activated. Here, the value of the shear stresses acting in a fragment of the medium, as well as corresponding ultimate values of shear strain and dilatancy, at which the fault zone could be activated, are essentially dependent on the ratio and dynamics of change of the local values of some stress tensor invariants. Among them are pressure and stress intensity (von Mises stress). This is due to the fact that these parameters determine the ability to operate in the geological medium of one of a key deformation mechanism that is associated with the formation and evolution of damages at the interface of the structural elements in the block structure medium. In particular, the decrease in the pressure in the medium fragment at relatively low levels of stress intensity can lead to an increase in ultimate shear strain and dilatancy at the beginning stages of activization of the fault zone. At the same time a significant increase in the stress intensity while decreasing the pressure could lead to a decrease in the shear strength of the geomedium.