砂卵石地层台阶法施工隧道围岩-支护结构应力应变特性三维离散元分析

为了解砂卵石地层隧道围岩和支护结构的应力应变特性，以青海循隆高速公伯峡隧道为依托，借助PFC3D离散元软件对公伯峡隧道穿越砂卵石地层进行三维模拟，重点研究以密排短管棚预支护为根本前提，以三台阶预留核心土为施工方法的砂卵石地层围岩和支护结构的应力应变特性，并与现场实测进行对比分析。研究结果表明： 隧道台阶开挖时，围岩应力集中范围逐渐从拱顶过渡到拱腰，直到拱脚，对应的塑性区范围不断扩大，且密排短管棚对塑性区的发展有一定的“遮拦效应”； 围岩横纵向变形规律一致，主要是向隧道临空面产生收敛变形，且密排短管棚形成的梁拱效应限制了掌子面前方位移发展； 2种方法得到的初期支护变形规律一致，均呈阶段性变化，拱顶下沉累计值大于周边收敛累计值，且两者的最终变形量均满足规范限值要求。

3D DEM Analysis of Stress strain Behavior of Tunnel Surrounding Rock support Structure by Benching Method in Sandy Cobble Stratum

In order to understand the stress strain behavior of tunnel surrounding rock and supporting structure of in sandy cobble ground and based on the Qinghai Xun long Expressway Gongboxia tunnel, the 3D simulation of the tunnel construction in sandy cobble stratum is performed by PFC3D. The stress strain behavior of surrounding rock and supporting structure in sandy cobble Stratum is mainly studied with the premise of densely packed short pipe shed pre support and three bench reserved core soil method, and which is compared to the field measurement. The results show that: (1) when tunnel is excavated, the range of rock stress concentration gradually changes from the vault to the hance, until the skewback, and the corresponding plastic zone range is continuously expanded. Besides, the densely packed short pipe roof has a certain "obscuring effect" on the development of the plastic zone. (2) the deformation laws of the surrounding rock for transverse and longitudinal are consistent, which mainly converge to the tunnel free face. And the beam arching effect formed by the densely packed short pipe roof restricts the development of the displacement in front of the tunnel face; (3) the initial support deformation laws obtained by the two methods are consistent, both showing staged changes. The cumulative value of the vault settlement is greater than that of the surrounding convergence, and the final deformation of which can both meet the specification limit.