Experimental study on the mechanical properties weakening mechanism of siltstone with different water content

The mechanical properties of rock materials are remarkably affected by water content. To reveal the effect of water content on the strength and deformation properties of siltstone, which was collected from the quarry of Zhundong Coalmine, the scanning electron microscope and uniaxial compression tests of siltstone specimens were carried out with a water content of 0%, 0.5%, 1.5%, and 2.8%. Conventional triaxial compression test was conducted in dry and saturated conditions. The test results showed that the strength and deformation parameters of siltstone are weakened with different degrees after water absorption. The deformation of the plastic yield stage in the stress-strain curve decreases with rising of water content, while the loss rate of uniaxial compression strength continues to increase until reached saturated state. The strength of dry and saturated specimens varies regularly with confining pressure, and their relationship can be described with the exponential criterion. In addition, it is observed that microscopic damage of siltstone specimens accumulates as water content increases. The hydration of clay minerals reduces the local cohesion of specimens, and the hydrolysis of quartz minerals in crack tip region promotes subcritical crack growth during the loading process, which collaboratively results in the bearing capacity of saturated specimen decrease. The results can provide a reference for the analysis of rock strength and damage mechanism under the action of water erosion.