基于峰后特征的深部隧道围岩分层断裂数值分析

苏永华　毛克明　梁斌　付雄　贺炜

摘要：为了揭示深部隧道工程围岩的分层断裂机理而展开数值实验研究.分析了深部地层岩体历史及赋存环境，认为深部岩体在力学上处于峰后阶段，根据岩石峰后应力应变特征选定了围岩的峰后特征指标及其开挖响应方程.建立了数值实验模型，设计了开挖数值模拟的围岩响应监控方案.完成了大量的开挖数值模拟，实现了深部围岩分层断裂现象在数值模拟中的重现.基于实验中围岩应力、变形分布的全程监测结果，在确定围岩分层断裂产生条件的基础上，进一步研究得到了围岩分层断裂层数、分层断裂圈半径、最大峰值应力等参数与峰后特征指标的关系.根据地下结构开挖围岩应力重分布及岩石力学破裂机理，分析了分层断裂中次生自由面、多重似开挖面形成的力学机制.所得数值模拟结果，为深部工程围岩的分层断裂提供了验证依据，消解了长期以来数值模拟中没有观察到分层断裂现象的困惑.

关键词：深部隧道；分层断裂；应变软化；峰后脆性；力学机制

中图分类号：TU458 文献标识码：A

Abstract：Numerical simulation research has been conducted in order to reveal the mechanism of the layered fracture within surrounding rock in deepburied tunnel. Analysis of the history of the rock mass and its environment suggests that the mechanism of the deep rock mass was located in the postpeak stage， the postpeak characteristic indexes and the excavation response equations were selected based on the postpeak stressstrain characters of rock mass. A numerical model was established， a monitoring scheme of surrounding rock response was designed which was caused by excavation， and a fair amount of excavation was completed by numerical simulation method， and the phenomenon of layered fracture within surrounding rock was reproduced in the numerical simulation. According to the monitoring results about the rock stress and deformation distribution from the experiment， and based on the critical conditions under which the layered fracture in surrounding rock was emerged， the relationship of the fracture layer number of surrounding rock， the radius of layered fracture zone and the maximum peak stress with the postpeak characteristic indexes were studied. Based on the surrounding rock stress redistribution related to the excavation of underground structure and the fracture mechanism of rock mechanics， this paper analyzed the mechanical mechanism of the formation of secondary freesurface and multiple excavation surface. The numerical results provide the basis for the layered fracture in deep surrounding rock， and the confusion about the unobserved phenomena of layered fracture in numerical simulation is also eliminated.

Key words：deepburied tunnel； layered fracture； strainsoftening； peakbrittleness of rock； mechanicalmechanism

由于煤炭、石油、国防以及核废料处理等领域向地层深部或超深部挺进，深部岩体的开挖变形问题已引起了岩土工程界的广泛重视.传统的观测和理论公认，地下工程开挖后仅在靠近临空面围岩形成单一破裂带.但在深部工程开挖及相关试验中，发现围岩表现出不同于浅部工程的破裂区域分布，即非经典破裂现象.

俄罗斯学者E.I.shemyakin等＼[1＼]通过模型试验获得了分区破裂化现象，并在深部开采中得到电阻率法测试结果的证实.李术才等＼[2＼]通过临界值定义，在淮南矿区丁集煤矿深部巷道围岩中通过钻孔电视成像仪观察到了分区破裂化.周小平等＼[3＼]运用弹性力学和断裂力学理论，研究了破裂区和非破裂区的宽度和数量问题.李英杰等＼[4＼]探讨了围岩分区破裂机理，认为它是劈裂破坏现象.李树忱等＼[5＼]通过对围岩或数值单元的破坏进行重新定义或改造后，利用FLAC3D的模拟获得围岩的分区破裂图像，并简要讨论了不同因素的影响程度.苏永华＼[6＼]等研究了原岩应力场对分层断裂的影响.