ABSTRACT
New methods for limit and residual strength certificates construction were developed. The results of tests which including loading monolithic solid specimens of irregu- lar shape by spherical indenters are needed.
The method of construction the strength certificate of intact rock is based on an estimate of the inhomogeneous stress state when it is loaded with spherical indenters. Tensile and compressive components of cohesive shear strength were taken for definition characteristics of specimen failure.
Residual rock strength certificate is constructed according to the data on the strength of solid rock, in accordance with the established dependencies on the rock brittleness index and taking into account its lithological composition.
It is proposed to approximate the envelope curve of Mohr's stress circles by linear seg- ments corresponded to stable types of destruction, and transitional curvilinear segments for which the type of failure have the probabilistic nature.
A complex method for estimating the strength of fractured rocks is proposed. It is based on results of mechanical testing of specimens with spherical indenters. Strength of the rock is determined by comparing the indicators of the limit and residual strength of solid specimens, taking into account the parameters of fracture in the natural conditions.
Correlations which depend of the strength parameters of fractured rocks on the stress level and rock brittleness index are set.
It's recognized that plotting an empirical envelope curve based on Mohr's stress circles (strength certificate) allows researcher to make a complete representation about rock's strength characteristics in different stress conditions. Thus the computational method for strength certificate construction was developed in Saint Petersburg Mining University. This method is based on estimation of rock's anisotropic stress condition and on estimation of specimen complex failure mechanism caused by loading it with counter moving spherical indenters (Korshunov, 2010). In the course of further research, the method is improved.
