The Uniaxial Creep Characteristics of Red Sandstone under Dry-Wet Cycles

Abstract

Water is one of the most important factors that affect the long-term stability of geotechnical engineering structures. Rainfall often results in periodic changes in the water content in underground rock, which is subjected to alternating dry-wet cycles. In this paper, in order to study the short-term and long-term mechanical properties of red sandstone under these dry-wet cycles, a series of uniaxial compressive strength (UCS) tests and multistage creep tests have been carried out on specimens of red sandstone after being treated to different numbers of dry-wet cycles. A scanning electron microscope (SEM) was used to image the different groups of specimens. The test results have shown that the peak strength and the elastic modulus of the red sandstone decreased as the number of dry-wet cycles increased. It is worth noting that the first immersion of the specimens decreased their strength the most, and the negative logarithmic function was able to better reflect the peak strength of the red sandstone and the variation of its elastic modulus in relation to the number of dry-wet cycles. The results of the creep tests have shown that the instantaneous strain and creep strain of the sandstone increased significantly with the increase of the number of dry-wet cycles. A linear function and a negative logarithmic function can be used to describe the instantaneous strain and the creep strain, respectively. The creep duration of the red sandstone in its failure stage decreased with the increase of the number of dry-wet cycles, and the creep rate increased with the increase of the number of dry-wet cycles. Lastly, the failure modes of the red sandstone were observed; the results showed that the angle between the main crack and the axis of creep failure gradually increased with the increase of the number of dry-wet cycles and the angle of the internal friction and the cohesion decreased. In addition, the failure mode of the specimens changed from tensile failure to shear failure. The microstructure of the sandstone showed that the surface of the specimen changed from being compact to being loose, and the mineral particles in the specimen changed from being spherical to being flat and curly; this led to a decrease in the macroscopic mechanical parameters of the sandstone.