图  1  砂岩石窟顶板塌落破坏现象

Fig.  1.  The collapse and failure phenomenon of sandstone carved roof

图  2  砂岩石窟顶板拉裂破坏过程示意图

a. 石窟造像区地层分布；b. 降雨入渗；c. 层理面渗流；d. 裂隙产生；e. 悬臂拉裂式破坏

Fig.  2.  Schematic diagram of the fracture process of sandstone carved roof

图  3  试验设置

Fig.  3.  Test setup

图  4  劈裂试验试样受力情况

Fig.  4.  The force of the split test sample

图  5  不同条件砂岩试样抗拉强度

Fig.  5.  Tensile strength of sandstone samples under different conditions

图  6  不同循环次数试样裂纹扩展过程

Fig.  6.  Crack growth process of samples with different cycles

图  7  不同循环次数试样裂隙萌生及裂隙贯穿的发生时间

Fig.  7.  The time of crack initiation and crack penetration of samples with different cycles

图  8  不同循环次数试样的应变场变化（a）干燥试样（b）饱和试样

Fig.  8.  Strain field changes of samples with different cycles (a) dry samples (b) saturated samples

图  9  巴西劈裂试验及三轴压缩试验的莫尔应力圆

Fig.  9.  Mohr stress circle of Brazil split test and triaxial compression test

图  10  不同循环次数试样的内摩擦角及粘聚力

Fig.  10.  Internal friction angle and cohesion of samples with different cycles

图  11  试样显微薄片分析

a. 5次循环；b. 15次循环；c. 25次循环；图中：Q. 石英；Kf. 钾长石；Pl. 斜长石；Cl. 粘土矿物；Cal. 方解石

Fig.  11.  Analysis of sample microscopic slices

图  12  应力应变曲线阶段划分

Fig.  12.  Stage division of stress-strain curve

图  13  试样的应力应变曲线及裂纹起始应力$ {\mathit{\sigma }}_{\text{c}\text{i}} $和裂纹损伤应力$ {\mathit{\sigma }}_{\text{c}\text{d}} $

a. 干燥试样；b. 饱和试样

Fig.  13.  The stress-strain curve of the sample and the initial crack stress $ {\mathit{\sigma }}_{\text{c}\text{i}} $ and the crack damage stress $ {\mathit{\sigma }}_{\text{c}\text{d}} $

图  14  破坏模式划分

Fig.  14.  Classification of failure modes