Experimental study on the effect of water on mechanical properties of swelling mudstone

Water has a significant effect on the mechanical properties of rocks, especially for rocks containing swelling clay minerals. The clay minerals in swelling rocks will lead to volume expansion and disintegration of rocks after encountering water. In order to further study the water effect on mechanical properties of swelling mudstone, the swelling property of samples was first evaluated by the oedometric swelling test. Then, uniaxial compression tests, Brazilian disc tests, triaxial compression tests, and scanning electron microscope tests were carried out on the swelling mudstone samples (from Xinjiang, China) with different water content. The results showed that the various strengths (uniaxial compressive strength, tensile strength and triaxial compressive strength) of the mudstone samples all decreased with the increase of water content. Furthermore, with increasing water content, the elastic modulus decreases, while the peak strain decreases first and then increases. The strength envelope under each water content was constructed and the relevant parameters were obtained. It was found that the internal friction angle did not change with the water content, but the cohesion decreased with the increase of water content. The reasons of the deterioration of cohesion were explained by scanning electron microscopy tests. Finally, a complete empirical formula for predicting the mechanical properties of swelling mudstone is established.