不同循环上限荷载下泥质石英粉砂岩力学特性试验研究

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

通过开展循环加卸载转单调加载试验和疲劳破坏试验,揭示循环荷载下泥质石英粉砂岩的变形和力学响应特征。试验与研究结果表明,当循环上限荷载位于疲劳强度前后,试件的轴向和横向累计残余应变由单调递增凸曲线向凹曲线延伸,滞回环间距由“疏-密”向“疏-密-疏”发展,残余应变率和滞回环相对面积由L形向U形转化;弹性模量由初始快速上升、下降、缓慢稳定发展3个阶段向单调递减凹曲线转凸曲线衰减;而横向-轴向应变比则由单调递减凹曲线,转变为单调递增凸曲线,然后向凹曲线延伸;随上限荷载的增加,循环加卸载3000次后泥质石英粉砂岩抗压强度先增大后减小,最大增幅较单轴抗压强度高13.62%,而当上限荷载小于单轴压缩弹性上限时,循环荷载作用后的岩石抗压强度略小于单轴抗压强度;当试件发生疲劳破坏时,疲劳寿命与上限荷载呈幂函数分布,疲劳强度约为单轴抗压强度的80%~89%。试件弹性模量整体随着循环上限荷载先增大后减小,而横向-轴向应变比则随上限荷载的增加而增大;提出了循环荷载的“薄弱结构断裂效应”和“压密嵌固效应”,探讨了循环加卸载过程中多孔弱胶结岩石的强度变化特征和力学参数演化机制。

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.