Effect of moisture on the mode of deformation and failure of coal measure mudstone under triaxial compression

In the paper are presented the results of triaxial tests on the deformational and strength properties of a certain Carboniferous hydromiica-kaaoinite mudstone with siderite, occurring at great - reaching one thousand meters - depths in the first colliery of the recently developed Lublin Coal Basin. The rock is weak and very sensitive to the presence of water. Mine roadways driven in this rock are very soon closed as a result of intensive floor heave and high deformational rock pressure on the support. Air-dry and water-saturated specimens of the mudstone were subjected to the conventional triaxial compression tests at confining pressures.up to 60 MPa, at room temperature, with strain rates of the order of 10−6/s. The aim of the investigations was the determination of the effect of confining pressure and moisture content on the mode of rock deformation in the pre- and post-failure states. As a result of the triaxial tests, the criteria of linearity and nonlinearity of longitudinal strain have been determined, the constitutive equations for the stresses below and above the limit of linearity (elasticity) have been formulated, and the criteria of the limiting state (brittle fracture and plasticity) have been determined. The formulas expressing the dependence of the basic material constants on confining pressure have been given. The results will be used in a numerical analysis of the state of stress and displaeement of the rock mass in the vicinity of mine workings excavated in the first collieries of the Lublin Coal Basin.