拉张盆地不同埋深复合地层中隧道围岩变形破坏数值模拟研究

NUMERICAL SIMULATION OF DEFORMATION AND FAILURE OF SURROUNDING ROCKS OF TUNNELS IN MIXED STRATUM WITH DIFFERENT DEPTHS IN EXTENSIONAL BASINS

不同埋深的软硬岩层叠置复合地层变形破坏形式复杂而使得软岩大变形和硬岩岩爆位置相关关系不够明确。在拉张盆地中自重应力为主,侧压系数一般较小且多数在1.0以内。本文以在水平和铅垂叠置复合地层中TBM开挖圆形断面隧道为例,采用有限差分程序FLAC^(3D)对拉张盆地中不同埋深、不同叠置型式复合地层中TBM开挖后的三维弹塑性位移变形、主应力和塑性破坏分布变化特征展开数值模拟研究。模拟结果表明,围岩变形主要发生在软岩层地层中,埋深超过800 m后沿隧道轴向软岩大变形藕节状分段开始显现;随埋深增加,硬岩稳定性变差,顶拱位移增加尤其明显;随埋深增加,软岩和硬岩地层之间主应力差异变小,硬岩中储能明显;埋深越大塑性区分布范围越大;埋深较小时岩层以拉张破坏为主,埋深较大时以剪切破坏为主,两种状态的转换埋深(临界深度)约为800 m。由此对拉张盆地中深埋界限值给予了理论验证。

The deformation and failure patterns of the surrounding rocks of tunnels in mixed ground composed of soft and hard strata are complex at different depths.Under the gravity stress operated in extensional basins,the lateral pressure coefficient is generally small and basically within 1.0.This paper takes the TBM excavation of circular caverns in horizontal and vertical superimposed mixed ground as an example.It uses the finite difference numerical simulation software FLAC^(3D)to study the displacement,principal stress and failure characteristics of different superimposed mixed ground along the tunnel axis under different depths in extensional basins.The results show that the deformation of surrounding rock mainly occurs in soft rock.With the increase of depth,the stability of hard rock becomes worse,especially the displacement of the top arch in working face increases obviously.When the buried depth is more than 800 m,the large deformation as nodal segments of soft rock along the tunnel axis begins to appear.With the increase of depth,the difference in principal stress between soft rock and hard rock becomes smaller.The larger the depth is,the larger the distribution range of plastic zone is.The tensile failure is the main deformation in small depth,while the shear failure is the main deformation in large depth.The transition depth(critical depth)of the two states is about 800 m.Therefore,the limit value of deep burial in extensional basin is theoretically verified.