循环荷载下干燥与饱和砂岩力学特性及能量演化

Mechanical properties and energy evolution of dry and saturated sandstones under cyclic loading

对取自陕北榆横矿区小纪汗煤矿顶板砂岩的干燥及饱和试件进行单轴循环加、卸载试验,分析了干燥与饱和状态下岩石的强度和变形特征以及岩石破坏过程中的能量演化与能量分配情况。结果表明:(1)循环加、卸载导致干燥试件的峰值强度较单轴压缩时下降19.47%;(2)饱水对砂岩的强度和变形均有影响,饱和试件的平均峰值强度比干燥试件低39.55%,同时饱和试件具有更加明显的压密阶段;(3)循环加、卸载下砂岩的加载和卸载弹性模量均呈现增大趋势,但饱和试件的弹性模量低于干燥试件;(4)通过峰值强度归一化处理后发现,在应力加载的不同阶段,饱和试件的弹性应变能Ue和耗散能Ud均低于干燥试件;(5)加载过程中,饱和试件弹性应变能Ue的占比高于干燥试件,该比例随着加载过程逐渐下降并在破坏前与干燥试件的Ue的占比达到近似水平。

In this study, uniaxial cyclic loading and unloading experiments were conducted on dry and saturated sandstones from Xiaojihan coal mine in Shaanxi province, respectively. The strength and deformation characteristics of rock and its corresponding energy evolution and distribution during the process were analyzed. It is found that the peak strength of dry specimens under cyclic loading and unloading condition was 19.47% lower than that under uniaxial compression condition. The results demonstrate that the saturation affects both the strength and deformation of sandstone specimens. Compared with dry specimens, the average peak strength of saturated specimens was 39.55% lower, meanwhile, the saturated specimens present more obvious compaction stage. The loading elastic modulus and unloading elastic modulus tend to increase for dry and saturated sandstones. However, the elastic modulus of saturated specimens was lower than that of dry ones. When the peak strength was normalized, the elastic strain energy Ue and the dissipation energy Ud of dry specimens were larger than those of saturated specimens at different stages of stress loading. During the loading process, the proportion of elastic strain energy Ud of saturated specimens was greater than that of dry one. In addition, the Ud proportion of saturated specimens declined gradually during the loading process. The Uc proportions of dry and saturated specimens achieved an appropriate level prior to failure.