隧洞开挖围岩动态卸载响应特征模拟研究

考虑隧洞瞬态开挖卸载并分析围岩的动态响应对研究其变形破坏机制非常重要。在静水压力圆形隧洞动态卸荷模型理论分析的基础上，采用FLAC3D的Fish语言开发了隧洞开挖动态卸载围岩响应模拟计算程序。验证算例模拟结果与理论结果对比，证明了程序的正确性，围岩的应力变化和体积应变增量均呈现由表及里的波浪型变化，能较好地模拟围岩的动态卸荷响应。根据Griffith强度准则计算得到的不同时刻围岩的损伤范围表明，考虑动态卸载时围岩的损伤区比采用静态分析要大。采用该程序分别模拟了不同卸载时间、卸载路径、隧洞形状、隧洞直径、地应力等条件下，隧洞动态卸载围岩的动态响应。结果表明，在卸载时间变短、先慢后快卸载路径、洞形为方形、洞径变大和地应力差值增大的条件下，隧道围岩内最大、最小主应力应力差也增大。深部隧洞采用瞬态卸载分析对于深入研究围岩变形破坏机制具有重要意义。

Simulation of dynamic response of surrounding rock under the tunneling-induced unloading

In studying the deformation and failure mechanism associated with tunneling, it is very important to consider the transient excavation-induced unloading effect and analyze the dynamic response of surrounding rock. Based on the dynamic unloading model of a circular tunnel under hydrostatic pressure, a procedure for simulating dynamic unloading response of tunnel excavation is developed by using Fish language in FLAC3D. A numerical example is analyzed and the results are compared to the theoretical results, showing the validity to the proposed procedure. It is shown that the stress and volumetric strain of the surrounding rock vary in a wavy manner and the proposed procedure can be effectively used to simulate the dynamic unloading response of the surrounding rock. Based on the calculated damage range using the Griffith strength criterion, it is found that surrounding rock damage area is larger than that of the static analysis with considering the dynamic unloading effect. The proposed procedure is applied to analyze the dynamic response of the surrounding rock under different unloading conditions including unloading time, unloading path, tunnel shape, tunnel diameter and ground stress and so on. It is shown that as the unloading time decreases, the unloading path increases in a way gradually to drastically, and the tunnel diameter increases, and that with the increase of geostress and its difference, the difference between the maximum and minimum principal stresses increases. The proposed instant unloading analysis procedure can provide new insights into the deformation and failure mechanism of the surrounding rock of deep buried tunnels.