真三轴压缩下砂岩的能量和损伤分析

Energy and damage analysis of sandstone under true triaxial compression

为了探究真三轴压缩下砂岩的能量和损伤演化规律,利用自主研发的真三轴扰动卸荷岩石测试系统进行真三轴一次加卸载试验和真三轴压缩试验,对真三轴压缩应力-应变演化规律进行研究,探讨三向主应力加、卸载的对岩体的影响,利用图形面积积分法分别计算了真三轴压缩的弹性能密度、耗散能密度与输入能密度,分析三者随最大主应力卸载水平增加的规律及其相互之间的关系,进一步研究真三轴压缩过程中损伤演化规律,并对冲击地压倾向性判定条件弹性能量指数进行讨论。研究结果表明:真三轴压缩下最大主应力增大,使砂岩内部应力调整,从而引起中、小主应力方向应变变化,从能量角度定义该现象为能量“诱增”;划分了三个方向主应力加、卸载的种类,将加载分为损伤加载(最大主应力加载)与保护加载(中、小主应力加载);将卸载分为常规卸载(最大主应力卸载)与损伤卸载(中、小主应力卸载);真三轴压缩下中间主应力方向约束应力较大,使得该方向“诱增”弹性能密度比例高于最小主应力方向“诱增”弹性能比例;真三轴压缩下最大主应力方向应力提升,砂岩的弹性能密度、耗散能密度均与输入能密度之间存在线性函数关系,提出了真三轴压缩的能量分析方法,进一步得到了砂岩的储能极限,与单轴压缩相比,其储能性有较大提升;真三轴压缩下砂岩损伤变量在塑性阶段之前岩石损伤呈近似线性变化,随着最大主应力增加,损伤变量呈非线性演化趋势。

In order to explore the true triaxial compression under the energy and the damage evolution law of sandstone,with independent research and development of disturbance unloading rock true triaxial test system for a real triaxial unloading test and true triaxial compression test,the evolvement of true triaxial compression stressstrain are studied,and the influence of the principal stress on rock mass is discussed.The elastic energy density of true triaxial compression,dissipation energy density and input energy density are calculated by graphics area,and their variations with the unloading level of the maximum principal stress are analyzed.The damage evolution law of the rock mass during the true triaxial compression process,and the elastic energy index for determining the tendency of impact ground pressure is discussed.The results show that the increase of the maximum principal stress under true triaxial compression makes the internal stress of sandstone adjust,resulting in the change of strain in the direction of medium and small principal stress.This phenomenon is defined as“induced increase”of energy from the perspective of energy.The types of principal stress loading and unloading in three directions were divided into damage loading(maximum principal stress loading)and protection loading(medium and small principal stress loading).Unloading is divided into conventional unloading(maximum principal stress unloading)and damage unloading(medium and small principal stress unloading).Under true triaxial compression,the confining stress in the middle principal stress direction is larger,making the proportion of induced elastic energy density in this direction higher than that in the direction of minimum principal stress.The stress of maximum principal stress direction increases under true triaxial compression,and there is a linear function relationship between the elastic energy density,dissipated energy density and input energy density of sandstone.The energy analysis method of true triaxial compression is proposed,and the energy storage limit of sandstone is further obtained.Compared with uniaxial compression,its energy storage capacity is greatly improved.The damage variable of sandstone under true triaxial compression changes approximately linearly before the plastic stage,and presents a nonlinear evolution trend with the increase of maximum principal stress.