大理岩破坏阶段Biot系数研究

Study of Biot's coefficients of marble during plastic deformation phase

在流固耦合研究中经常采用有效应力原理,Biot系数的确定为其中困难之一。为了研究含裂纹大理岩中Biot系数演化规律,在三轴压缩塑性变形后期阶段的不同轴向变形条件下,进行轴向压力加卸载循环;并在轴向压力卸载末期对岩样施加孔隙水压力。通过记录试样的变形,在Shao提出的Biot系数计算方法的基础上,计算轴向和侧向Biot系数。得到了不同围压条件下轴向和侧向Biot系数随轴向变形的演化规律,并对此进行了深入分析。结果表明:(1)Biot系数表现为各向异性,三轴压缩试验时,试样中大部分裂纹沿最大正应力方向扩展,是造成这种现象的直接原因;(2)轴向和侧向Biot系数随着轴向变形的增大而增大,轴向变形的增大引起岩样中裂纹扩展,导致Biot系数增大;(3)低围压条件下轴向和侧向Biot系数均比高围压条件下的值大,这是由于破坏方式不同引起的。

The concept of effective stress is mostly used in hydro-mechanic coupling study, while it is difficult to determine the values of Biot＇s coefficients. A test system is developed to study the evolution of Biot＇s coefficients in cracked rock materials induced by deviatoric stress. In the plastic deformation phase of triaxial compression test, some loading-unloading cycles of axial stress were carried out at different levels of axial strains. After injection and squeeze water into/out of the specimen at the end of axial stress unloading process, the deformation is recorded during the loading-unloading cycle of pore pressure. The Biot＇s coefficients in axial and lateral directions are calculated based on the method proposed by Shao. The evolution of axial and lateral Biot＇s coefficients at different levels of axial strains is presented in a series of confining stresses; it is found that： 1 ） the property of Biot＇s coefficients is anisotropic, it is reasoned that the cracks in the specimen are grown along the direction of maximum normal stress; 2） the axial and lateral Biot＇s coefficients are increased when axial strain increases, the increasing of axial strain leads to the propagation of cracks, consequently causes the Biot＇s coefficients augment; 3） the values of axial and lateral Biot＇s coefficients under low confining stress are greater than the one under high confining stress, the reason is that the failure style is changed with confining stress.