Abstract
Studying the mechanical properties of soft rocks subjected to water and cyclic loading would contribute to a better understanding of the stability analysis of soft rock engineering under the conditions of storm and carrier dynamics. In this paper, two soft rocks from Southwest China (i.e., muddy siltstone and silty mudstone) were selected as test samples. Uniaxial compressive tests were applied to investigate the strength and deformation characteristics under water-rock reactions. Meanwhile, triaxial tests were carried out to analyse the fatigue damage and failure characteristics by applying cyclic axial loading under different confining pressures. The results indicated a reduction in the uniaxial compressive strength (UCS) under saturated conditions, which is correlated with the disintegration resistance of soft rocks. Moreover, the samples exhibited a softening phenomenon due to water absorption and rock expansion, decreasing the elastic modulus. The triaxial tests demonstrated that axial strain accumulated with the number of loading cycles due to fatigue and even failed when applying increased cyclic loading with certain cycles. The cohesion decreased during cyclic loading, but the friction angle was relatively independent of the number of cycles. In addition, reductions in the dynamic elastic modulus and shear modulus decreased with increasing loading time. This study indicated that water and cyclic loadings could cause significant degradation of the strength and stiffness of soft rocks, which need to be considered carefully during the engineering utilization of such materials.
Highlights
As a common geotechnical material, soft rocks, which cause prominent engineering geology problems, are widely distributed in Southwest China. e soft rock is integral, exhibits considerable mechanical strength in its natural state, and has been selected as a backfill subgrade material
The peak compressive strength of the saturated rock samples was significantly lower than the peak compressive strength of the natural samples, which decreased from 25.76–21.35 MPa to 17.04–7.07 MPa for muddy siltstone and from 17.65–9.94 MPa to 11.3–5.59 MPa for silty mudstone
Rock Degradation Subjected to Cyclic Loading. e degradation processes of muddy siltstone and silty mudstone were studied according to the experimental method described previously and are shown in Figures 2 and 3. e figures illustrate the curves of axial accumulated strain εd with the number of cyclic loadings N for different combinations of confining pressures with the dynamic load. e results showed that the axial accumulated strain tended to be stable or increased slowly after 2000 loading cycles, indicating that some rock samples did not fail at this time, and the effect of cyclic loading on the soft rock was only a small amount of plastic deformation
Summary
As a common geotechnical material, soft rocks, which cause prominent engineering geology problems, are widely distributed in Southwest China. e soft rock is integral, exhibits considerable mechanical strength in its natural state, and has been selected as a backfill subgrade material. E soft rock is integral, exhibits considerable mechanical strength in its natural state, and has been selected as a backfill subgrade material. This material softens or even collapses after the impact of water [1,2,3]. Research on the waterrock reaction mechanism is detailed and complex work that needs to investigate the influence of the type, hydration properties, and expansive behaviours of clay minerals on the microstructure of soft rock. It was not enough to explain the mechanism of the water-rock reaction by only the content of clay minerals, and more meticulous work needs to be performed to study the interaction between water and soft rock.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
