EXPERIMENTAL STUDY ON THE MECHANICAL PROPERTIES OF ARGILLACEOUS QUARTZ SILTSTONE UNDER DIFFERENT UPPER LIMIT CYCLIC LOADINGS

Cyclic-to-monotonic loading tests and fatigue damage tests were conducted to reveal the deformation characteristics and mechanical properties of argillaceous quartz siltstone under cyclic loading. When the upper limit loading was changed from less than to greater than the fatigue strength, both the axial and lateral cumulative residual strains extended from a monotonically increasing convex curve to a concave curve. The hysteresis loop distance evolved from "sparse-dense" to "sparse-dense-sparse". The residual strain rate and relative area of hysteresis loop was changed from L-shaped to U-shaped. The elastic modulus evolved from three stages of initial rapid rise, decline, and slow and steady development to monotonically decreasing concave curve to convex curve. The lateral-to-axial strain ratio was changed from a monotonically decreasing concave curve to a monotonically increasing convex curve, and then extended to a concave curve. With the increase of the upper limit loading, the rock compressive strength of the argillaceous quartz siltstone was first increased and then decreased after cyclic loading of 3000 times. The maximum value was 13.62% higher than the uniaxial compressive strength. When the upper limit loading was less than the uniaxial elastic limit, the rock compressive strength after the cyclic loading was slightly less than the uniaxial compressive strength. When fatigue failure occurred, the relation between the fatigue life and the upper limit loading exhibited a power function distribution. The fatigue strength was approximately 80%~89% of the uniaxial compressive strength. With the increase of the upper limit loading, the elastic modulus first increased and then decreased, while the lateral-to-axial strain ratio continually increased. The weak structural fracture effect and the compaction effect under cyclic loading on rock are proposed, which can explain the strength characteristics and mechanical parameters evolution law of porous weak cemented rock under cyclic loading.