Experiment effect study of equivalent confining pressure on mechanicalproperties of coal and rock under condition of true three axis

In order to study the strength and deformation characteristics of coal and rock under horizontal stress loading,the true three axis test was carried out under different stress conditions in laboratory.The test results show that the peak strength of three axis compression increases with the increase of the minimum principal stress and vertical stress,defined the“equivalent confining pressure”to describe the mechanical properties of coal should be under the stress level,the peak strength and the complex peak strain of the specimens increase linearly with the increase of the equivalent confining pressure; the number of cracks produced by the failure of coal and rock increases with the increase of equivalent confining pressure and the breaking angle increases with the increase of equivalent confining pressure into two times.The stress level of coal affects its mechanical properties,the test results have important theoretical support and practical significance for efficiency mining and safe production of deep coal and rock.