正断型断裂模拟及其对山岭隧道影响研究

Simulation of normal fault rupture and its impact on mountain tunnels

活动断层的运动和与其相交山岭隧道的震害密切相关,是隧道抗震设计所面临的严峻挑战之一。为此,以滇中引水工程香炉山隧洞为研究背景,运用断裂力学中的黏性界面模型结合有限元方法模拟正断层破裂过程。通过震害调查和试验结果对三维自由场的响应进行验证。进一步建立跨断层隧道三维数值分析模型探讨了不同断层错动量和倾角对隧道响应的影响规律,并引入损伤指数建立隧道安全评价的分类标准对结构的震害进行初步评估。结果表明:正断层错动所引起的地表破裂机制主要有弯曲陡坎和断裂陡坎;隧道衬砌的轴向拉应变和环向剪应变在其与断层滑动面相交位置处达到最大;断层错动量和倾角的变化对隧道不同震害状态沿纵向分布有明显影响;随断层倾角的增大,隧道衬砌处于严重损伤和完全损毁状态的长度要明显减小,断层倾角在50°~70°时对结构安全更为不利。

The seismic damage of mountain tunnels is closely associated with the movement of active faults.Seismic design of tunnels crossing active faults is one of the great challenges nowadays.Based on the engineering prototype of the Xianglu mountain tunnel,the water diversion project in central Yunnan Province,a numerical method to simulate the propagation of normal fault rupture is proposed using the finite element method incorporated with the cohesive interface model in fracture mechanics.The proposed method is verified against the post-earthquake reconnaissance and experimental results using the three-dimensional free-field model.It is used to simulate a tunnel crossing a normal fault,and the effects of fault displacement and dip angle on the response of the tunnel linings are discussed.Besides,the damage indices and safety assessment criteria are introduced to preliminarily evaluate the damage of the tunnel linings subjected to fault movement.The results show that the mechanisms of surface rupture exhibit the forms of folding or fault scarps under normal faulting.The axial tensile strain and hoop shear strain of the tunnel linings reach the maximum at the position where they intersect the fault slip surface.The seismic damage state of tunnel along the longitudinal direction is significantly affected by the fault displacement and dip angle.The length of the tunnel linings in a severely damaged and completely damaged state is significantly reduced with the increase of the dip angle.Dip angles of 50°to 70°are more detrimental to structural safety.