基于卸荷路径的软岩大变形隧道计算模型

Tunnel Calculation Model of Soft Rock Large Deformation Based on Unloading Path

近些年来,软岩大变形隧道施工带来的安全事故日益频繁,其主要原因是目前暂未形成有针对性的、可以准确反映软岩大变形力学行为的隧道计算模型。隧道开挖过程实际是一个卸荷的过程,在这种应力路径条件下,隧道塑性区内围岩的力学性能相对未开挖状态减弱。本文基于隧道典型软岩—泥岩卸荷三轴试验得到考虑峰后损伤的力学本构模型,并建立软岩隧道计算模型。与传统Fenner公式计算结果进行对比发现,本文模型更加符合高地应力下软岩隧道开挖和支护计算结果。利用Euler显式差分求解算法对模型进行理论求解,研究不同支护力、不同黏聚力、不同摩擦角、不同变形模量对隧道塑性圈半径与洞周位移的影响。基于FISH语言平台,将计算模型嵌入FLAC 3D得到了支护时间对支护效果的影响。最后基于龙溪隧道的现场实测数据验证了本文的隧道计算模型。研究成果可以为准确计算大变形段落围岩响应提供理论依据。

Tunnel excavation is actually an unloading process.Due to the influence of unloading stress paths,the parameters of the surrounding rock in the plastic zone of the tunnel are degraded and the mechanical parameters are reduced relative to the unexcavated state.In this paper,a model for calculating the reduced parameters of the surrounding rock in the plastic zone of the tunnel is obtained based on the typical soft rock-mudstone unloading triaxial test of the tunnel by other scholars.Comparing the results with the traditional Fenner formula,it is found that this model is more consistent with the results of excavation and support calculations for soft rock tunnels under high ground stress.The model is solved theoretically using the Euler explicit differential solution algorithm to study the effects of different support forces,cohesive forces,friction angles and deformation moduli on the radius of the tunnel plastic circle and the displacement of the perimeter of the tunnel.The model was developed using FISH language and embedded in FLAC 3D software to calculate the effect of different support timing on the support effect.Finally,the tunnel calculation model is validated based on the field measurement data of Longxi tunnel.The research results can provide a theoretical basis for the design of high ground stress soft rock tunnels.