基于连续-非连续分析理论的隧道围岩破坏区判识方法研究

Study on the identification method of tunnel surrounding rock failure zone based on continuous discontinuous analysis theory

准确分析隧道挖破坏区的范围对合理确定支护参数有着重要的指导作用和工程意义,主要围绕连续介质分析方法和以有限元-离散元耦合方法(finite element-discrete element coupling method,简称FDEM)为代表的连续-非连续方法开展了隧道围岩破坏区判识方法研究。研究了连续介质分析方法与FDEM识别围岩破坏的判别标准;将岩体划分为弹性的岩石单元和弹塑性的界面单元,基于等效连续模型的思想,推导了界面单元力学参数与岩石单元及岩体单元力学参数的关系表达式,首次建立这两种方法参数取值的联系,解决了连续-非连续方法取值难的问题;对比了两种方法模拟不同岩性、断面铁路隧道开挖过程中围岩破坏区范围。基于规范中各级围岩的力学参数取值范围,给出了各级围岩下以FDEM中罚参数和断裂能等围岩主要破坏参数的取值范围;FLAC3D为代表的连续介质方法和FDEM两种方法对不同岩性、断面铁路隧道开挖过程模拟结果表明,连续介质方法得出的塑性区和以塑性极限应变得出的破坏区域和连续-非连续方法得出的裂纹扩展区和破坏区在分布范围、形态及破坏形式上基本一致,验证了提出的FDEM围岩破坏参数取值方法是合理可行的。

Accurate analyzing the scope of tunnel excavation failure zone has important guidance and engineering significance in determining support parameters reasonably.This study focuses on the identification methods of tunnel surrounding rock failure zone,specifically the continuous medium analysis method and the continuous-discontinuous method represented by the finite element-discrete element coupling method(FDEM).Firstly,the continuous medium analysis method and FDEM identification criteria for surrounding rock failure are studied.Then the rock mass is divided into elastic rock elements and elastic-plastic interface elements.Based on the concept of equivalent continuous model,the relationship between the mechanical parameters of interface elements and rock elements and rock mass element is mathematically derived.The connection between the parameter values of these two methods is established for the first time,resolving the challenge of determining values in the continuous-discontinuous method.Finally,the ranges of surrounding rock failure zones simulated by these two methods during the excavation process of railway tunnels with different lithology and cross-sections are compared.According to the range of mechanical parameters for each level of surrounding rock mass in the specification,the range of values for the main failure parameters of surrounding rock,such as penalty parameter and fracture energy,in FDEM,is given for each level of surrounding rock.The simulation results of railway tunnel excavation with different lithology and cross sections using the continuous medium method represented by FLAC3D and FDEM method show that the plastic zone obtained by the continuous medium method,and the failure zone obtained by the plastic limit strain,as well as the crack growth zone and failure zone obtained by the continuous-discontinuous method,are generally consistent in terms of distribution range,shape and failure mode.The method proposed in this article for determining the failure parameters of surrounding rock in FDEM is verified as reasonable and feasible.