高地应力软岩隧洞开挖扰动特征与规律研究

Study on characteristics and rules of excavation disturbance of high ground stress soft rock tunnels

高地应力软岩隧洞由于地应力高,软岩强度及变形模量低,变形和破坏现象十分突出。以滇中引水工程香炉山隧洞为依托,研究了不同洞室形状和地应力场条件下,高地应力软岩隧洞围岩的变形和破坏特征。研究表明:隧洞开挖后,围岩应力、变形、破裂范围及支护结构受力均呈分区分布特征,大主应力传递轮廓和围岩变形轮廓基本呈垂直关系。对于高地应力软岩隧洞,"谐洞"并不是合理的洞形,"谐洞"虽然使切向应力在洞室边界上均匀分布,但切向应力向围岩内部的衰减速率沿短半轴方向(大曲率半径)较沿长半轴方向(小曲率半径)要小得多,导致软岩隧洞在高地应力条件下破裂范围更大;与此理念相反,通过在小主应力方向上设置小曲率半径,可更快形成高围压抑制围岩剪切破裂的进一步发展,减少围岩的破裂范围和变形程度。

Due to high ground stress,low strength and deformation modulus,the deformation and damage phenome⁃na are very prominent in high ground stress soft rock tunnel.Based on Xianglushan tunnel in the Central Yunnan Water Diversion Project,the deformation and failure characteristics of surrounding rock of high ground stress soft rock tunnel under conditions of different cavern shapes and initial stress field were studied.It was shown that the surrounding rock stress,deformation,rupture range and supporting structure load are characterized by zonal distri⁃bution after tunnel excavation.The maximum principal stress transfer profile and deformation profile of the sur⁃rounding rock are basically perpendicular.In addition,the"Harmonious hole"that forms the uniform distribution of the tangential stress along the boundary of the cavern is not a reasonable shape for soft rocks with high in-situ stress,the decreasing rate of tangential stress inside the surrounding rock in the minor semi-axis direction(large ra⁃dius)is much smaller than that in the major semi-axis(small radius)direction,which leads to larger rupture range under high in-situ stress.On the contrary,by setting a small radius of curvature in the minor principal stress direc⁃tion,a higher confining pressure can be formed to inhibit the further development of shear rupture of the surround⁃ing rock,thereby reducing the rupture range and deformation degree of the surrounding rock.