不同围压下卸荷速率对围岩变形与破坏的影响

Effects of the unloading rate on the deformation and damage of the surrounding rock under different confining pressures

研究相关因素对巷道/隧道围岩变形及破裂形态特征的影响作用,可以为巷道/隧道的支护设计提供理论支撑。在课题组已成功构建的围岩试件开挖卸荷模型试验系统基础上,对水泥砂浆围岩试件进行不同初始围压下不同卸荷速率的系列试验。试验结果表明:(1)开挖卸荷对围岩变形及破坏的影响不仅存在于卸荷阶段,卸荷效应会在卸荷结束之后继续对巷道围岩产生影响,并且随着初始围压的增大,对卸荷后围岩变形的影响更为明显。(2)卸荷阶段的切向、轴向应变率均呈现先增大后逐渐减小的变化趋势。快速卸荷应变率峰值出现较早,慢速卸荷应变率峰值出现较晚。(3)初始围压相同时,卸荷速度增大,卸荷阶段应变率加快,变形总量越小。卸荷速度相同时,初始围压增大,卸荷阶段应变率加快,变形总量越大。(4)慢速卸荷破坏时,试件外壁完整,内壁上靠近底端出现片状剥落;快速卸荷破坏时,试件外壁上出现环状贯通裂隙伴随少量竖向微裂隙,内径缩减明显,内壁上出现岩块掉落现象。试验结果有利于进一步研究其他相关因素对围岩变形及破裂形态的影响机制。

Investigations of the influence of correlative factors on deformation and fracture characteristics of roadways/tunnels surrounding rocks can provide theoretical support for the supporting design of roadways/tunnels. A test system for excavation and unloading of surrounding rock specimens was developed,and a series of tests with different unloading rates under different initial confining pressures were carried out on the surrounding rock specimens made of cement mortar. The test results show that the influence of excavation unloading on the deformation and failure of surrounding rock exists not only in the unloading stage but also in the stage after unloading,and the influence in the stage after unloading is more obvious with increasing the initial confining pressure. Both the tangential and axial strain rates during the unloading stage increase firstly and then decrease. The peak of the rapid-speed unloading strain rate appears earlier than that of the slow-speed unloading strain rate. When the initial confining pressure is same,the higher the unloading speed is,the faster the deformation rate in the unloading stage is and at the same time,the smaller the total deformation is. When the unloading speed is same,the higher the initial confining pressure is,the faster the deformation rate in the unloading stage is and the larger the total deformation is. It is observed that,when the surrounding rock specimen is destroyed in the slow-speed unloading test,the outer wall of the specimen is intact but the inner wall near the bottom flakes,and that,in the rapid-speed unloading test,annular cracks occur along the outer wall of the specimen accompanied by a small amount of vertical micro-fractures,the inner diameter is reduced obviously and the rock on the inner wall falls. The research is helpful to further study the influence of relevant factors on surrounding rock deformation law and surrounding rock rupture form.