坚硬围岩初期支护合理时机研究

Study on Primary Supporting Time for Hard Surrounding Rockmass

针对某水电站业已完成的地下厂房第一期开挖开展坚硬围岩初期支护的合理时机研究。首先,根据地下厂房围岩变形监测资料,研究分析了围岩位移变化率的时间效应及坚硬围岩的应力释放特征;其次,借助二维有限元分析软件Phase2,通过指定不同的应力释放系数来模拟不同的洞室支护时机,计算结果表明在不同应力释放阶段,围岩自承载能力和围岩变形均表现出阶段性发展的趋势;随支护时机推迟,支护应力减小,围岩塑性区和开挖变形量增大;同时考虑坚硬围岩应力释放的时间效应,研究围岩变形特征曲线,为初期锚喷支护的设置时机提供了可以测量、控制的研究手段。最后,综合不同支护时机下的支护抗力和围岩应力、变形分析表明:针对该水电站地下厂房坚硬围岩,应力释放达约60～70%或开挖通过施工断面15d左右是一个较为有利的支护时机。计算结果符合地下工程施工过程的一般规律,对于该水电站地下厂房正在进行的开挖支护活动具有很好的参考价值。

For the first-phase excavation of underground powerhouse in a hydropower project,the primary supporting time of hard surrounding rockmass is studied.Firstly,time effect of displacement ratio and stress releasing characteristics of the hard surrounding rockmass are analyzed based on deformation monitoring.Then,the different supporting schedules are simulated with the corresponding stress releasing coefficient by the two-dimensional FEM software Phase2.The result shows that the bearing capacity and deformation development of surrounding rockmass exhibit staged characteristics with different stress releasing coefficients,and support stress becomes less,the excavation displacement and rock plastic zone becomes larger with the supporting time postponed.A new method to study primary supporting time of hard surrounding rockmass is provided by considering time effect of deformation curve.Finally,based on calculation results with different supporting time,it reveals that it is an appropriate time to support when the stress releasing coefficient reaches to about 0.6～0.7 or excavation of some construction section passes through approximately 15d.The analysis methods have been verified and have some reference value for the further study on excavation and support of the hydropower project.