Effect of water and temperature on short-term and creep mechanical behaviors of coal measures mudstone

In the present study, a series of uniaxial compression tests and multistage creep tests were performed on specimens of coal measures mudstone with different water contents and at different temperatures using an electrohydraulic servo-controlled testing system (MTS816), a specially developed cantilever-type multiarm lever creep testing device and a thermostatic water tank. The effects of water and temperature on short-term strength, failure mode, and creep properties of the mudstone were systematically analyzed. The uniaxial compression test results showed that the presence of water has a significant effect on the mechanical strength and weakens the short-term mechanical properties of the mudstone specimens, whereas high temperatures can exacerbate this water-weakening effect. The uniaxial compressive strength of the specimens decreased exponentially, as the water saturation coefficient increased at room temperature, whereas the strength of saturated specimens decreased linearly with the increase in temperature. The multistage creep test results indicated that increases in the water saturation coefficient and temperature accelerate the creep deformation and creep strain rate of the mudstone specimens. Under different water and temperature conditions, the creep strain rate increased exponentially, as the creep stress level increased. The sensitivity of the creep strain rate to the creep stress level increased with the increase in water saturation coefficient and temperature. Based on the creep test results, linear rheological models were employed to fit the creep behavior of the mudstone. The results showed that the Burgers model can replicate the primary and secondary creep behaviors of the mudstone under different water content and temperature conditions. The parameters of the Burgers model (E_m, E_k, and η_m) generally decreased with the increase in water saturation coefficient and temperature. The reasons why water and temperature affect the short-term and long-term mechanical behaviors of the mudstone are the physicochemical effects and mechanical effects.