饱和岩体渗透性动态演化对引水隧洞稳定性的影响研究

Effect of the permeability dynamic evolution of saturated rock on the stability of diversion tunnels

水力耦合分析一直是水电站深埋引水隧洞稳定性研究的热点和难点。基于多孔介质有效应力原理,得到了改进后的饱和岩体孔隙率、渗透系数的动态演化模型,该模型能实现围岩体受力破坏全过程的水力完全耦合,然后通过子程序二次开发将模型嵌入到有限元软件ABAQUS中,计算分析某深埋引水隧洞施工开挖时的变形分布,与现场多点位移计监测结果对比,考虑渗透性动态演化的模型计算结果更符合工程实际,证明了模型和计算程序的准确性和合理性。为研究引水隧洞在运营期的充水和排水对围岩和衬砌的影响,通过数值仿真计算,与传统的视渗透系数为定值的工况对比,对于围岩,采用渗透性动态演化模型工况时得到的孔隙水压力分布在充水和排水后均变化较大,拱顶变形比渗透系数为定值要大接近100%、拱底位移要大接近180%~200%,塑性分布范围和屈服程度要远大于渗透系数为定值的工况;对于隧洞衬砌,从充水到排水,系数为定值工况时的衬砌最大拉力增长幅度约11%,而采用演化模型工况得到的衬砌最大拉力增长幅度约35%,且量值更大,应引起足够重视。

Hydro-mechanical coupling analysis has been a focus and difficulty in the study on the stability of deep buried diversion tunnels in hydropower station. Based on the effective stress principle of porous media,an improved model regarding the dynamic evolution of porosity and permeability of saturated rock with respect to volumetric strain is derived,which can realize the real hydro-mechanical coupling analysis in the process of failure of surrounding rock. Being introduced into the code ABAQUS through the secondary development of user-defined subroutines,the evolution model is applied to a large deep buried diversion tunnel. The calculation results by the proposed evolution model are compared with field monitoring data and traditional hydromechanical coupling calculation results in terms of the permeability distribution and displacement in the surrounding rock,and it is shown that the proposed model is more precise and more practical. In order to study the influence of filling and draining water on the stability of the diversion tunnel during operation period,a numerical simulation with 5 calculation steps is conducted. Compared the traditional case taking the permeability as an invariant,for the surrounding rock,the pore water pressure after the periods of filling and draining water decreases more rapidly from the border to deep ground,the displacement at the roof is much larger by up to 100% and larger by 180% to 200% at the floor,and the scope and extent of the plastic zone are far greater. For the lining of the tunnel,the tensile stress in the linings with a constant permeability increases by approximately 11% from filling water to draining water while the calculation result by the proposed evolution model increases by up to 35% with a larger value,which should be paid more attention.