State Key Laboratory for Geomechanics and Deep Underground Engineering, School of Mechanics and Civil Engineering, China University of Mining and Technology, Xuzhou, 221116, P.R. China.
Sci Rep. 2020 Feb 5;10(1):1900. doi: 10.1038/s41598-020-58595-2.
The long-term deformation and permeability evolution with time are key issues for geo-engineering applications such as radioactive waste disposal. Rock permeability concurrent with deformation is significantly influenced by cracking. This study investigated the creep-permeability evolution behavior of red sandstone specimens containing a single fissure under a confining pressure of 30 MPa. First, the effects of stress ratio (SR) and fissure dip angle on the creep behavior of rock were investigated. The more loading/unloading cyclic numbers, the larger the irrecoverable axial deformation. The instant elastic strains and visco-elastic strains linearly increased with SR for both the intact and fissured specimens, whereas the instant plastic strains showed different results. The visco-plastic strains nonlinearly increased. For fissured and intact specimens, the creep strains and the steady-state creep rates nonlinearly increased as SR increased. The instantaneous strains, instant elastic strains, and visco-elastic strains slightly varied when the fissure dip angle was less than 45° but notably decreased with increasing fissure dip angle beyond 45°. However, the fissure dip angle had no obvious effects on the plastic and creep strains. Damage (D) was defined using the ratio of non-elastic strains to the total strain. D increased approximately linearly with SR, but the fissure dip angle had no obvious influences. Subsequently, the long-term strength (LTS) of the red sandstone was determined using two different methods. The LTS first decreased when the fissure dip angle increased from 0 to 45° but increased with increasing dip angle. The triaxial and creep failure modes were mainly shear along anti-wing cracks for the fissured specimens but shear failure occurred for the intact specimen. Moreover, the permeability of the fissured red sandstone was governed by SR and deformation or time. During the multi-step loading/unloading creep process, the permeability first decreased and then had a sudden rise when tertiary creep occurred.
长期变形和渗透率随时间的演化是放射性废物处置等地质工程应用中的关键问题。岩石渗透率与变形的协同作用受裂纹影响显著。本研究在围压 30 MPa 的条件下，研究了含单裂隙红砂岩试样的蠕变-渗透率演化行为。首先，研究了应力比（SR）和裂隙倾角对岩石蠕变行为的影响。加载/卸载循环次数越多，轴向不可恢复变形越大。对于完整和裂隙试样，瞬时弹性应变和粘弹性应变随 SR 线性增加，而瞬时塑性应变则表现出不同的结果。粘塑性应变呈非线性增加。对于裂隙和完整试样，蠕变应变和稳态蠕变速率随 SR 的增加呈非线性增加。当裂隙倾角小于 45°时，瞬时应变、瞬时弹性应变和粘弹性应变略有变化，但当裂隙倾角超过 45°时，应变明显减小。然而，裂隙倾角对塑性和蠕变应变没有明显影响。采用非弹性应变与总应变的比值定义损伤（D）。D 随 SR 近似线性增加，但裂隙倾角无明显影响。随后，采用两种不同方法确定红砂岩的长期强度（LTS）。当裂隙倾角从 0°增加到 45°时，LTS 先降低后增加。裂隙试样的三轴和蠕变破坏模式主要为沿反翼裂纹的剪切破坏，而完整试样则发生剪切破坏。此外，裂隙红砂岩的渗透率受 SR、变形或时间控制。在多步加载/卸载蠕变过程中，渗透率先减小，然后在发生三级蠕变时突然升高。
