关键词: 泥质石英粉砂岩, 近疲劳强度, 循环荷载, 力学参数, 变形特征, 柔量

Abstract: Cyclic loading with the upper limit loading of 80% uniaxial compressive strength (UCS) and monotonic loading are consequently applied on argillaceous quartz siltstone. The evolution law of peak strength, dilatancy point stress, elastic modulus, Poisson’s ratio, hysteretic loop, strain, compliance and mechanical properties of the studied siltstone under cyclic loading near fatigue strength are studied. The test results show that: 1) With the increase of cycle numbers, the rock peak strength decreases slightly at first, then increases continuously, and finally tends to be stable. The minimum and maximum peak strengths are respectively 7.35% lower and 16.57% higher than the UCS. 2) There is a negative linear correlation between stress and the volumetric strain at dilatancy point. The ratio of stress corrseponding to dilatancy point at the last cycle to peak strength of different specimens follows a logarithmic function distribution with the number of cycles, and a formula is proposed to predict the uniaxial peak strength of rock after cyclic loading near fatigue strength. 3) The monotonic loading strain ratio and the peak strain ratio of the rock are stable around 0.58 and 1.02 after several cycles, respectively. It indicates that the deformation resistibility capacity of argillaceous quartz siltstone is significantly improved after cyclic loading near fatigue strength. The peak strain of uniaxial compression test can be used as the reference value of rock failure under cyclic loading. 4) In loading stage, the loading compliance corresponding to axial strain increases first and then decreases linearly, and the loading compliance corresponding to volumetric strain shows a hook shape. In unloading stage, the loading compliance corresponding to axial strain presents a trend of accelerating growth, and the loading compliance corresponding to volumetric strain shows a V-shape. The loading and unloading compliance corresponding to volumetric strain at the lower limit load exhibits positive linear correlation with the residual volumetric strain, which can reflect the accumulated damage of rock under cyclic loading. 5) Based on the evolution law of mechanical parameters and deformation, and the microstructure characteristics of argillaceous quartz siltstone, the evolution mechanism of peak strength and dilatancy point stress under cyclic loading near fatigue strength is revealed.

Key words: argillaceous quartz siltstone, near fatigue strength, cyclic loading, mechanical parameters, deformation characteristics, compliance