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千枚岩岩体具有遇水后软化、膨胀、强度降低等特点,有必要探明岩体软化后围岩的应力与应变特征,探究洞室成形后结构的变形及力学行为,寻求该种地层条件下合理的施工及支护方法。以穿越“5.12”地震发震断裂-龙门山断裂的某千枚岩隧道为背景,首先对干燥及地下水富集区域的洞周变形进行归纳总结,并以此为基础对岩体软化后的物理力学参数进行反演分析,表明了地下水的存在极大弱化了岩体的强度、刚度与抗变形能力;而后,通过将隧道变形及结构受力的计算结果与实测值进行对比分析,进而对施工过程中水对千枚岩软化后隧道结构的安全性及围岩稳定性做出评价。研究表明,对于强震区软岩隧道应结合现场实际情况选择预留变形值25～30 cm,位移控制基准30～35 cm,施工工法应在3台阶+预留核心土(台阶间距为1 m)基础上配合以机械方式开挖为主,微爆破方式为辅,支护则应选择强度及刚度大的结构形式,同时增强超前支护并在施工中重视各环节的工艺衔接可有效避免变形坍塌灾害,提高施工效率。
The phyllite rock mass has the characteristics of softening, expansion and strength reduction after water metamorphism. It is necessary to ascertain the stress and strain characteristics of surrounding rock mass after softening of the rock mass, to investigate the deformation and mechanical behavior of the structure after cavern formation, Under the conditions of reasonable construction and support methods. Based on a phyllite tunnel crossing the “5.12” earthquake and the Longmen Shan fault, the authors first summarize the deformation of the surrounding rock in the dry and groundwater-enriched area and use it as a basis for the softening of the rock masses The results show that the existence of groundwater greatly weakens the strength, stiffness and anti-deformation ability of rock mass. Then, by comparing the calculation results of tunnel deformation and structure stress with the measured values, The safety of tunnel structure and the stability of surrounding rock after the water softening of phyllite were evaluated during construction. The results show that for the soft rock tunnel in strong earthquake zone, the deformation value of 25-30 cm should be selected and the displacement control standard should be set at 30-35 cm according to the actual situation in the site. The construction method should be at 3 steps + reserved core soil ) Based on the combination of mechanical excavation-based, micro-blasting mode is supplemented, support should choose the strength and stiffness of the structure, while enhancing the advance support and attention in the construction of all aspects of the process of convergence can be effective in preventing deformation Collapse disaster, improve construction efficiency.