不同加卸载方式下饱和岩石力学特征的试验研究

为研究不同加卸载方式下饱和岩石的力学演化特征，开展了等增幅加卸载、多重加卸载和微扰动加卸载3种不同方式的加卸载试验，分析了不同加卸载方式下的岩石力学特征。结果表明，3种加卸载方式下各循环曲线大体呈下凹型; 等增幅加卸载下塑性阶段的各循环曲线会在应力峰值前突变为上凸型，并在加载段后期发生振荡，且出现越来越早的下跌; 多重、微扰动加卸载下曲线连续性好，首循环应变远大于多重或微扰动循环; 多重加卸载下，随着循环次数增加，应力零点处的曲线斜率越来越大，多重循环较首循环的加载曲线斜率大; 微扰动加卸载下，塑性阶段的卸载曲线为近似垂直线，加载段曲线斜率呈现“增-减-增”三段式变化。各加卸载方式下软化阶段、峰值应变的关系均为: 多重加卸载>等增幅加卸载>微扰动加卸载; 塑性阶段的长短关系为: 等增幅加卸载>多重加卸载>微扰动加卸载，而依此顺序岩石也由剪切破坏向张拉破坏变化。

Experimental Study on Mechanical Characteristics of Saturated Rock Under Different Cyclic Loading Modes

In order to study the mechanical evolution of saturated rock under different cyclic loading modes, experiments were performed with three different modes, including increasing amplitude (IA) cyclic loading, repeated increasing amplitude (RIA) cyclic loading, as well as disturbance increasing amplitude (DIA) cyclic loading. Also the mechanical characteristics of the rock under those three modes were analyzed. Results showed that under three different modes, each cycle of curve generally presented to be concave upward. Under IA cyclic loading, each cycle of curve at plastic stage abruptly changed into concave downward before reaching the stress peak value, and then oscillated at the later stage after loading, appearing to drop earlier and earlier. The stress-strain curves under another two modes showed good continuity, in which the strain in the first cycle was much larger than that in the subsequent cycles. Under RIA cyclic loading mode, the slope of stress-strain curve at the point of zero stress was getting larger and larger by increasing the number of cycles, and the slope of first cycle of curve was smaller than that of other cycle of curves. Under the DIA cycle loading mode, the stress-strain curve at plastic stage during unloading presented to be an approximately vertical line, and the slope of curve during loading stage presented a three-stage variation of “increase-decrease-increase”. The softening stage and peak strain under each cyclic loading mode could be arranged in the following descending order: RIA cyclic loading > IA cyclic loading > DIA cyclic loading. The length of plastic stage for each mode was in the following descending order: IA cyclic loading > RIA cyclic loading > DIA cyclic loading. And rocks were transformed from shear failure to tension failure under each mode according to this order.