An Experimental Study on Stress Relaxation of Yunnan Sandstone

This study presents the results from five relaxation tests conducted under uniaxial compression at room temperature. Test specimens were from sandstone formations at a mine, in Yunnan, and exhibited brittle failure. The test apparatus was valid for conducting stress relaxation experiments on sandstones by theoretical model and deformation measurements. Multiple load levels were applied in steps to each specimen, with each displacement level maintained for 12 d or longer. As soon as axial stress was decreased, it stabilized at an almost constant value after 12-24 h. Three distinct relaxation phases were observed to exist at all displacement levels except the specimen 3 in all tests. Based on the LM-NLSF method, model parameters under different strain levels were obtained. Comparison of test curves with theoretical curves showed that the Burgers model, which considers damage, was suitable for describing the stress relaxation properties of sandstones and the obtained parameters had a certain practical value.