含2条软弱夹层的隧道围岩开挖过程破坏模式研究

软弱夹层是山岭隧道常遇的不良地质现象，目前关于多条软弱夹层对隧道围岩稳定性的研究尚不多见，为加强该方向的研究，采用模型试验和数值模拟研究含2条软弱夹层隧道围岩开挖过程中的破坏模式。基于实际工程背景，设计模型试验，从裂隙损伤演变、应力场及应变场变化规律3个方面得到相吻合的破坏模式：首先拱顶受剪应力影响，沿软弱夹层发生滑移，进入塑性区；然后左、右拱肩受张拉应力影响，发生了塑性变形，出现张拉裂隙；接着右拱脚受剪、拉应力影响，进入塑性区；最后左拱脚受拉、剪应力影响，进入塑性区。采用FLAC^3D软件对试验进行模拟，将模拟结果与试验结果进行对比，并分析含单条软弱夹层和含2条软弱夹层隧道围岩破坏模式的差异性。结果表明：数值模拟结果与试验结果吻合良好；2条软弱夹层的存在会抑制软弱夹层下方隧道的水平收敛；隧道顶拱之上塑性破坏区域与水平面的倾角更小，表现出更危险的破坏趋势；顶拱区域、左拱脚与左中墙连通面应作为不利区域重点考虑；含2条软弱夹层的隧道围岩破坏模式有不同于单软弱夹层的规律，基于单条软弱夹层的支护方案进行设计、施工不能满足围岩稳定要求。

Failure Modes of Rocks Surrounding Tunnel with Two Weak Interlayers During Excavation

A weak interlayer is an unfavorable geological condition often encountered in mountain tunnels. However, investigations with two weak interlayers are still rare. Both physical model tests and numerical analyses were carried out to investigate the failure modes of rocks surrounding tunnels with two weak interlayers during the process of tunneling. Based on the project background, physical model tests were designed, and by identifying the characteristics of the crack damage, stress, and strain of the test model, three similar results were obtained as follows:First, under shear force, the vault developed plasticity and slipped along the interlayer. Second, plastic deformations occurred at the left and right arch shoulders, and tensile fractures developed. Third, the right arch foot developed plasticity because of shear and tensile stress. Finally, the left arch foot developed plasticity because of shear and tensile stress as well. In addition, FLAC^3D was used to simulate the experiment, and the simulation result was in good agreement with the experimental results. Based on the numerical simulations, the comparison of failure mode between tunnels with a single weak interlayer and two weak interlayers was conducted. It is found that the horizontal convergence below the weak interlayer is suppressed, and the dip angle of plastic failure zone over the vault and horizontal plane is smaller owing to the existence of two weak interlayers, which shows a more dangerous failure tendency. Besides, vault areas and connection between the left arch foot and the left middle wall should be considered as unfavorable areas. As the failure mode rule of a tunnel with two weak interlayers is different from that of one interlayer, it is unreasonable to adopt the schemes of design and construction of tunnels with one weak interlayer to meet the stability of those with two interlayers.