加卸载条件下石英岩蠕变–渗流耦合规律试验研究

Creep-seepage coupling laws of quartzite under cyclic loading-unloading conditions

以大东山隧道的石英岩为研究对象,进行循环加卸载条件下岩石蠕变–渗流耦合试验,分析了岩石加卸载过程中的蠕变、渗透性变化规律和渗流–蠕变耦合机理,得到压密阶段、裂纹扩展阶段和裂纹贯通阶段岩石体积应变的发展规律,总结了渗透率与体积应变之间的关系。试验表明:轴向荷载0~50 MPa为压密阶段,继续加载则产生不可恢复变形,当达到160 MPa时蠕变曲线进入加速段;随着轴向荷载水平的增加,渗透率总体趋势先降低后增高,最小值出现在最大压密点,蠕变过程进入加速段以后渗透率急剧增大。采用FLAC3D中的Cvisc模型为蓝本,以体积应变为桥梁建立ZSI(zone state index)与渗透率的关系,自主开发了基于应变软化的改进非线性蠕变西原模型,对试验结果进行验证。数值模拟表明:靠近进水端的渗透率比出水端变化快,不同应力下ZSI值云图的破损区与试验中岩样的"V"型剪切带破坏模式基本一致,渗透率的理论曲线与计算曲线吻合较好。说明提出的模型能够很好地反映加卸载条件下岩石蠕变–渗流耦合特性和局部破坏规律。

The quartzite of Dadongshan Tunnel is taken as the research object to carry out rock creep and seepage coupling experiments under cyclic loading-unloading conditions. The creep characteristics, permeability and seepage-creep coupling mechanism are analyzed. The development laws of volumetric strain in the phase of densification, crack propagation and crack coalescence are acquired. The relationship between permeability and volumetric strain is summarized. It is indicated that the axial loads between 0 and 50 MPa are in compression phase. If the loads increase, the unrecoverable deformation will be generated. When the loads reach up to 160 MPa, the creep curve enters into the accelerating period. With the increase of axial load level, the general tendency of permeability first decreases and then increases, and the minimum value appears at the largest densification points. After the creep process enters into accelerating period, the permeability sharply increases. Using the Cvisc model from FLAC3D as the basis and by introducing the zone state index（ZSI） into the volumetric strain, the relationship between ZSI and permeability is established. Numerical simulations are conducted to verify experimental results by adopting a nonlinear creep Nishihara model based on the strain softening. The results show that the permeability along with the development of the time in the process of loading near the inlet side of the permeability changes quickly. The damaged area of ZSI contours is coincided basically with the failure mode of the test samples in the ＂V＂-typed shear zone. The theoretical curves are in good agreement with the numerical ones. The proposed model can reflect the creep-seepage coupling characteristics and the local failure rules of rock under loading-unloading conditions.