加卸载围压条件下岩石峰后力学特性试验研究

发布时间：2018-08-11 11:27

【摘要】：岩石的峰后力学特性对充分发挥岩体的承载力以维持地下工程的稳定性、揭示岩体中塑性区的演化发展及岩体工程支护优化设计起着关键作用。因此,研究加卸载围压条件下岩石峰后力学性质对工程设计有着非常重要的意义。本文通过对岩样在残余强度阶段的加卸载围压试验,研究岩石峰后的力学特性,提出了峰后弹性滑移力学机理,并据此建立了数值分析模型,对隧道围岩变形进行数值分析。主要研究内容及结论如下:(1)常规三轴试验中岩石残余强度的大小受峰值强度和围压的影响,在低围压下表现更强的围压敏感性;这是由于低围压下破裂面间只有少量接触,作用力较小,随着围压的增大,接触面逐渐变得规整且面积增大,接触作用增强,应力-应变关系也由脆性跌落向塑性滑移转变;页岩峰值至残余阶段主要发生的是内聚力的丧失过程,而内摩擦角弱化量很小。(2)残余阶段加卸载围压试验中,卸载围压对残余阶段力学特性的影响在多次卸载-多次加载围压、多次卸载-一次加载围压和循环加卸载围压这三种试验方案中具有相同的规律,即在轴向应力处于初始残余阶段限定轴向位移不变,当围压以均匀的速度卸载时,轴向应力也相应地均匀降低;卸载围压至设定值后,轴向应力在施加轴向位移荷载后保持基本稳定,轴向应力-应变关系呈现塑性变形特征。(3)加载围压后,轴向应力-应变曲线可分为三个阶段,第一是在限定轴向位移情况下加载围压时轴向应力随围压增加而增大的轴向应力恢复阶段,第二是稳定围压后施加轴向位移荷载时轴向应力-应变具有与峰前相同的线弹性变形阶段,第三是当轴向应力达到残余应力时产生的弹性滑移变形阶段。(4)残余阶段的力学机理可以简化为弹性岩石块体沿破裂面的摩擦滑移变形。(5)基于岩石残余阶段的弹性滑移作用机理,提出了岩石峰后单结构面的弹性滑移模型,并通过ANSYS的接触单元模拟峰后破裂面间的摩擦滑移作用;模拟了不同围压下三轴压缩试验过程,结果表明模型与实际试验具有较好的拟合性。(6)基于峰后弹性滑移模型,用ANSYS模拟的隧道围岩变形能够很好地反映隧道围岩的变形特性。岩体峰后的沿弱面的滑移变形是隧道围岩变形的主要原因。
[Abstract]:The post-peak mechanical properties of rock play a key role in giving full play to the bearing capacity of rock mass to maintain the stability of underground engineering and to reveal the evolution and development of plastic zone in rock mass and the optimum design of rock mass engineering support. Therefore, it is very important for engineering design to study the post-peak mechanical properties of rock under loading and unloading confining pressure. In this paper, through loading and unloading confining pressure test of rock samples at the stage of residual strength, the mechanical properties of rock after peak are studied, and the mechanism of elastic slip after peak is put forward. Based on this, a numerical analysis model is established to analyze the deformation of surrounding rock in tunnel. The main research contents and conclusions are as follows: (1) in conventional triaxial tests, the residual strength of rock is affected by peak strength and confining pressure, and it is more sensitive to confining pressure under low confining pressure, which is due to the fact that there is only a small amount of contact between fracture surfaces under low confining pressure. With the increase of confining pressure, the contact surface becomes regular and the area increases, the contact action increases, and the stress-strain relationship changes from brittle drop to plastic slip. The loss of cohesion occurs mainly in the peak to residual stage of shale, but the weakening of internal friction angle is very small. (2) in the loading and unloading confining pressure test of residual stage, the influence of unloading confining pressure on the mechanical properties of residual stage is from multiple unload to multiple loading confining pressure. There are the same laws in the three test schemes of multiple unloading-one loading confining pressure and cyclic loading and unloading confining pressure, that is, when the axial stress is at the initial residual stage, the axial displacement is limited to be invariable, and when the confining pressure is unloaded at a uniform speed, After unloading the confining pressure to the set value, the axial stress remained basically stable after the axial displacement load was applied, and the axial stress-strain relationship showed the plastic deformation characteristic. (3) after loading the confining pressure, the axial stress remained basically stable after the axial displacement load was applied. (3) after loading the confining pressure, the axial stress-strain relationship showed plastic deformation characteristics. The axial stress-strain curve can be divided into three stages. The first is the axial stress recovery stage in which the axial stress increases with the increase of the confining pressure when confining pressure is loaded under the condition of limited axial displacement. The second is that the axial stress-strain has the same linear elastic deformation stage as before the peak when the axial displacement load is applied after stabilizing the confining pressure. The third is the elastic slip deformation stage when the axial stress reaches the residual stress. (4) the mechanical mechanism of the residual stage can be simplified as the friction slip deformation of the elastic rock block along the fracture surface. (5) based on the elastic slip mechanism of the residual stage of the rock, The elastic slip model of the single structure plane behind the peak of rock is proposed, and the friction slip between the fracture surfaces after the peak is simulated by the contact element of ANSYS, and the triaxial compression test process under different confining pressures is simulated. The results show that the model fits well with the actual test. (6) based on the post-peak elastic slip model, the deformation of tunnel surrounding rock simulated by ANSYS can well reflect the deformation characteristics of tunnel surrounding rock. The slip deformation along the weak plane behind the rock peak is the main reason of the tunnel surrounding rock deformation.
【学位授予单位】：重庆大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TD315

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