Experimental Study On Mechanical Properties Of Water Content Sandstone Under Confining Pressure

While rock of underground engineering is in the environment of complex geological mechanics, its mechanical properties are greatly affected by the factors such as the groundwater, ground stress and external load etc. Aiming at the unity deficiency of the previous experimental factors, the mechanical properties of sandstone considering of the combined factors of the water content, strain rate and confining pressure is to be studied on. The common red sandstone is taken as the research object. Firstly, according to the status of the method of water content rock sample preparation, the method that air-bleed quickly is studied and tested. Then quickly prepared aqueous sandstone samples by vacuum extraction method, carried out for aqueous sandstone under low strain rate on RMT301 rocks and concrete test system single triaxial test, determined the influence of three factors on rock mechanics parameters, and analyzed the mutual relationship between the factors affected. Finally, carried out the comparative study of Segmented damage constitutive model of sandstone based on different distribution under moisture content and strain rate. In order to provide theoretical support for the structural design of underground engineering support, long-term stability of surrounding rock and engineering safety assessment by using the results.According to the experimental study, it is concluded that it has a logarithmic relation between the rock water content and the test time of different rock by vacuum pumping method and the obtained natural immersion method. The performance that three factors influence the mechanical properties of sandstone are water weakening effect, strain rate strengthening effect and confining pressure hardening effect. In the uniaxial state, there is a certain fitting relationship between moisture content, strain rate and sandstone strength, the peak strain, elastic modulus and deformation modulus. In the triaxial state, there is also certain fitting relationship between confining pressure and sandstone mechanical parameters, but this situation, the relation become complicat between moisture content, strain rate and sandstone mechanical parameters. There is a certain interaction between the three factors. Overall, the increasing of the confining pressure will reduce the water weakening effect and the strain rate hardening effect; the increasing of the water content will lead to increase the confining pressure hardening effect and reduce rate hardening effect in the uniaxial strain; while the increasing of the strain rate will reduce the hardening effect of confining pressure and increase the water weakening effect in the uniaxial state. The damaged forms of the sandstone is mainly influenced by the confining pressure and there is no obvious relationship between water content and the damaged forms, however, along with the increasing of the strain rate, the form of shear failure appears easily. In the uniaxial compression tests, the damage constitutive model with considering the segment of the compaction state is superior to the one with considering the traditional whole stage and the damage constitutive model that based on the power function distribution is superior to the one that based on Weibull distribution.