进尺对浅埋隧道掌子面稳定性及变形受力影响

基于强度折减有限元法分析不同进尺对隧道掌子面稳定性和破坏形态的影响,研究不同进尺下掌子面变形形态、拱顶沉降特性、地表沉降槽形状,并揭示不同进尺下掌子面前方、进尺开挖段、支护段的应力传递路径、拱效应特征及应力演化过程。结果表明:进尺对稳定性的影响呈现非线性特征,整体上随着进尺的增大,稳定安全系数降低,塑性分布范围增大,位移影响范围增大,且从掌子面附近逐渐扩展到开挖段,位移矢量角呈现非线性增大,即竖向位移所占比重增加。掌子面前方及进尺开挖段均存在拱效应,竖向拱效应大于横向拱效应,水平拱效应最弱,应加强掌子面底部围岩的稳定和已支护段的强度;根据竖向应力距掌子面距离的不同,可以将其分为三个区段:掌子面附近为应力降低区,即卸荷区;掌子面前方一段距离为应力升高区,即应力承载区;掌子面较远处,为原岩应力区。

Influence of Excavation Footage on Shallow Tunnel FaceStability and Deformation and Mechanics

The effect of different footages on tunnel face stability and failure mode was studied based on the strength reduction finite element method. Tunnel face deformation morphology, crown settlement characteristics and surface settlement trough shape under different footages were analyzed, as well as the stress transmission path, arch effect characteristics and stress evolution process of the place in front of tunnel face, excavation footage and supporting section. The results were compared with numerical simulation and Vermeer formula and a parametric analysis was performed at last. The main conclusions are as follows: the influence of footage on the tunnel stability is nonlinear. The stability safety factor is reduced and the plastic displacement distribution range is increased with the increase of footage in the whole. The influence range of displacement is also increased and gradually extended to the excavation section from the tunnel face. The displacement vector angle is increased nonlinearly, namely the proportion of vertical displacement is increased. The arch effect exists in front of the tunnel face and excavation section. The vertical arch effect is larger than the transverse arch effect; the horizontal arch effect is the weakest. Hence, the stability of the surrounding rock at the bottom of the tunnel face and the strength of the supporting section should be reinforced. According to the different distances from the vertical stress to the tunnel face, the stress can be divided into three sections. Specifically, a section near the tunnel face being the stress relaxation area, namely the unloading area, a section in front of the tunnel face being the stress increasing region, namely the stress bearing area and the arch effect zone, and a section far from the tunnel face being the protolith stress zone.