应变软化模拟与圆形隧道衬砌分析

在岩土工程中，有许多类岩体呈现应变软化特性。在应变软化过程中，如果多个材料强度参数分析发生变化，就很难给出软化问题的解析解。已有的文献研究表明，在经典的弹塑性理论框架下，模拟岩土介质的应变软化过程依然值得深入研究。利用应变软化材料强度参数随塑性应变增加而弱化的特点，提出了将应变软化过程简化为一系列的脆性应力跌落与塑性流动过程的思想，应变软化行为的模拟转化为一系列脆塑性过程的分析。将这种模拟应变软化过程的思想方法用于求解均匀初始应力场中应变软化介质内的圆形隧道开挖问题，研究了衬砌对减少岩土开挖扰动的作用以及考虑应变软化对衬砌内力的影响。数值结果表明，对于应变软化岩土材料，忽略其强度软化的行为是偏于危险的。

Modeling of strain-softening and analysis of a lining for circular tunnel

In geotechnical engineering, many types of rock masses behave in a strain-softening way. It is not easy to get the closed form solution when strength parameters change in the strain-softening process. Literature review shows that the strain-softening problem has not been sufficiently analyzed within the framework of the classical theory of elastoplasticity. Based on the characteristics of strain-softening material in which the strength parameters change while the plastic strain increases, a new method for solving strain-softening problems is proposed. In the proposed numerical scheme, stress-strain curve in the strain-softening stage is approximated in a stepwise way; and the processes of the strain-softening is simplified as a series of stress drop and plastic flow during the increase of plastic strain. Therefore, modeling a strain-softening problem becomes a series of brittle-plastic analysis. The approach is employed to examine the circular opening excavation in a homogeneous and isotropic rock mass subjected to a hydrostatic in situ stress. The effect of lining on the plastic region and deformation in the surrounding rock mass is analyzed; and the influence of strain-softening behaviour is also discussed. Numerical results indicate that it is unsafe to ignore the strength decrease when tunnel excavation and liner installation are carried out in the strain-softening rock mass.