隧洞围岩在超载和卸载状态下的破坏模式

Failure Mode of Surrounding Rock of Tunnel Under Overloading and Unloading Conditions

围岩破坏模式分析是地下工程围岩稳定性分析、控制和支护设计的基础。围岩开挖是一个径向应力减小、轴向应力增大的复杂加卸载过程,当前常采用超载试验研究隧洞围岩的破坏模式。围岩的应力路径是影响其破坏模式的重要因素,而超载试验的围岩应力路径不同于加轴压、卸围压路径。为对比隧洞围岩在不同应力状态下的破坏模式,利用WE–600B型液压式万能试验机和自主设计的隧洞模型试验仪,采用相似模型试验方法,研究隧洞围岩在超载和开挖卸载过程中的应变演化规律及破坏面发展过程。应变演化规律方面:两种工况下,拱底均产生一定的拉应变;开挖卸载模式下,侧墙和拱腰处的应变增速大于超载模式,围岩向临空面的变形速度更快,破坏发展更快。破坏面发展方面:超载时,直墙两侧围岩整体剥落,剥落体保持完整;开挖卸载模式下,直墙两侧围岩向临空面逐层挤压溃曲,剥落体的完整性差,即开挖卸载路径下的围岩破碎程度更大。超载工况下,破坏过程由低应力时的拱底拉裂转变为高应力时的侧墙拉剪耦合的“V”型片帮剥落破坏;两种卸载工况下,破坏过程均为侧壁楔体剪切破坏和竖向张拉破坏耦合的“V”型片帮劈裂破坏。

The failure mode analysis of surrounding rock is the basis of stability analysis,control,and support design of surrounding rock in underground engineering.The excavation of surrounding rock is a complex loading and unloading process with radial stress decreasing and axial stress increasing,but the failure mode of surrounding rock of tunnels is often studied by overloading tests.As an important factor affecting its failure mode,the stress path of surrounding rock in overload test is different from that of confining pressure unloading with axial compression.To compare the failure modes of tunnel surrounding rock under different stress states,the strain evolution law and failure surface development process of tunnel surrounding rock during overload and excavation unloading process were studied by utilizing the WE–600B hydraulic universal testing machine and self-designed tunnel model tester.In terms of strain evolution law,both conditions produced a certain tensile strain at the bottom of the arch,while the strain growth rate of the side wall and arch waist in the excavation and unloading mode was higher than that in the overload mode,and the deformation speed of surrounding rock towards the blank surface was faster and the failure was more severe in the excavation and unloading mode.In the development of the failure surface,the surrounding rock on both sides of the straight wall was peeled off under tunnel overloading,and the peeled body remains intact,however it was extruding and crushing to free space and the integrity was very poor during ex-cavation unloading,indicating that the crushing degree of surrounding rocks under the excavation and unloading path was greater.During over-loading condition,the failure process from the tensile cracks of arch bottom under low stress state transits into the tensile-shear coupling“V”shape peeling failure of the side walls under high stress state.The failure model was wedge failure and vertical tension fracture coupling“V”shape splitting failure when the tunnel was under two kinds(60%σzmax and 100%σzmax)unloading conditions.