节理岩体卸荷各向异性力学特性试验研究

 针对节理岩体开挖卸荷所产生的各向异性力学难题，通过制作不同倾角单一预制节理试件，开展节理岩体三轴卸荷试验，研究卸荷条件下节理岩体的应力–应变关系、变形特征、强度特征和破坏模式。得到如下结论：(1) 进入卸荷阶段之后，0°，30°和90°倾角节理试件的应力–应变曲线依次出现屈服、软化和残余变形阶段，而45°和60°倾角节理试件只出现屈服阶段。(2) 节理试件的变形模量随节理倾角呈U型变化，其中，60°倾角节理试件的变形模量最小；随着围压升高，不同倾角节理试件之间的变形特性差异逐渐减小。(3) 0°，30°和90°倾角节理试件的抗压强度降低，而45°和60°倾角节理试件几乎未降低；节理试件的黏聚力随节理倾角呈U型变化，其中，60°倾角节理试件仍为最小；而内摩擦角随节理倾角增大而增大。(4) 0°，30°和90°倾角节理试件的破坏模式均为穿越节理的压剪破坏，且不受节理影响，而45°和60°倾角节理试件的破坏模式均为沿节理面滑动破坏。(5) 揭示节理岩体的卸荷力学特性分为受岩块强度控制和节理面强度控制。

EXPERIMENTAL STUDY ON ANISOTROPIC MECHANICALCHARACTERISTICS OF JOINTED ROCK MASSES UNDER UNLOADING CONDITION

The triaxial unloading tests on the precasted rock samples of a single joint with different dip angles were conducted to investigate the anisotropic mechanical behaviour of jointed rock masses under excavation including the stress-strain curves，the deformation and strength characteristics and the failure modes. (1) The stress-strain curves of jointed samples with dip angles of 0°，30° and 90° had a yield phase，a softening phase and a residual phase upon unloading，while the samples with dip angles of 45° and 60°had a yield phase only. (2) The variation of the deformation moduli versus the angles of joint inclination is in U-shape and the deformation modulus of the sample with the dip angle of 60°is the smallest. The differences of the deformation characteristics of different samples decreased gradually with the increasing of the confining pressure. (3) The compressive strengths of the samples with dip angles of 0°，30°and 90°were reduced，and those of the samples with dip angles of 45°and 60°were changed little. The cohesion versus the angle of joint inclination is in U-shape. The cohesion of the sample with the dip angle of 60°is also the smallest. The internal angle of friction increased with increase of the angle of joint inclination. (4) The failure modes of the samples with dip angles of 0°，30°and 90° were all shear failure across the joint surface and were not effected by the joint. The samples with dip angles of 45°and 60° were sliding failure along the joint surface. (5) It was revealed that the unloading mechanical characteristics of the jointed rock masses were controlled by the strengths of both rocks and joint surfaces.