穿越活动断裂带深埋隧道围岩地震响应分析

Seismic Response Analysis of Surrounding Rock of Deep Buried Tunnel Crossing Active Fault Zone

西南艰险山区道路和铁路隧道工程占比大,存在着埋深大、地质条件复杂、地震活动频发的特点,还存在隧道工程与活动断裂小角度穿越的工程问题,且近场地震对不同埋深的围岩影响不同,因而活动断裂近场地震对隧道工程顺利施工和安全运营存在显著不利影响。基于此,本文首先基于国内外发生的多次灾难性地震对隧道工程的影响,分析归纳了历史地震震级对穿越发震断裂隧道围岩(围岩埋深、岩性和级别)破坏的影响规律。其次,结合活动断层等特性,获取了能够反映区域断层特征和脉冲特性的地震动记录。最后,采用有限差分软件FLAC3D研究了活动断裂近场地震对深埋隧道工程围岩的影响规律。研究结果表明:隧道埋深的增加使得隧道围岩更加稳定,对于隧道围岩的塑性变形有抑制作用。不同地震动作用下的最大剪应力和最大主应力走势基本相同,断层段隧道围岩应力均大于普通围岩段。IV级及以下围岩在200 m埋深、PGA在0.3g以上时发生了较大的位移和应力响应。响应水平随着PGA的增大而增加,PGA从0.2g到0.39g的过程中有一个较大的增加,增幅接近50%,此过程是隧道产生塑性变形的主要过程,塑性区面积也随着PGA的增大而逐渐增大,因而在穿越活动断裂深埋隧道需认真考虑其近场地震的影响。研究成果可为隧道抗震优化设计提供技术支撑。

Tunnel engineering accounts for a large part of the road and railway projects in the dangerous mountains in southwest China.This area has large tunnel burial depth,complex geological conditions and frequent seismic activities.There are several engineering problems with small angle crossings between tunnel engineering and active faults.In addition,near-field earthquakes have different influences on surrounding rocks with different burial depths.Therefore,near-field earthquakes of active faults have significant adverse influences on the smooth construction and safe operation of tunnel engineering.Therefore,based on the impact of multiple disastrous earthquakes at home and abroad on tunnel engineering,the influence rules of historical earthquake magnitude on the damage of surrounding rock(surrounding rock burial depth,lithology and grade)of tunnels passing through the seismogenic fault are analyzed and summarized.Combined with the characteristics of active faults,the ground motion records that can reflect the regional fault characteristics and pulse characteristics are obtained.Finally,the finite difference software FLAC3D is used to study the influence of the active fault near-field earthquake on the surrounding rock of deep tunnel engineering.The results show that the tunnel surrounding rock is more stable with the increase of tunnel buried depth,which can restrain the plastic deformation of tunnel surrounding rock.The trend of maximum shear stress and maximum principal stress under different ground motions is basically the same,and the stress of tunnel surrounding rock in fault section is greater than that in ordinary section.The surrounding rock of Grade IV and below has a great displacement and stress response when the depth of tunnel is 200m and PGA is larger than 0.3g.The response level increases with the increase of PGA,and there is a large increase of nearly 50%in the process of PGA from 0.2g to 0.39g.This process is the main process of tunnel plastic deformation,and the area of plastic zone gradually increases with the increase of PGA.Therefore,the influence of near-field earthquakes should be carefully considered in deep-buried tunnels through active faults.The research results can provide technical support for seismic optimization design of tunnel.