卸荷时间对圆形巷道围岩开裂及径向应力波传播影响的数值模拟

采用提出的连续-非连续方法,研究了卸荷时间(卸荷快慢)对圆形巷道围岩开裂、径向应力波传播及围岩径向应力随时间演变规律的影响。该方法借鉴了拉格朗日元法、变形体离散元法及虚拟裂纹模型的思想。首先,研究了卸荷时间对围岩开裂的影响;然后,研究了卸荷时间对径向应力波传播的影响;最后,研究了卸荷时间对围岩径向应力随时间演变规律的影响。结果表明:卸荷越快,围岩中产生的裂纹越多,最大不平衡力越大,波动越剧烈。增加卸荷时间,开挖边界附近的开裂位置由连续分布向间隔分布转变:当卸荷时间较短时,开挖边界附近围岩呈现连续分布的开裂形态,与这些位置的最大主应力均超过抗拉强度引起拉裂有关;当卸荷时间适中时,围岩呈现出与V形坑类似的开裂形态,可能与这些位置存在剪应力有关。卸荷越快,处于扰动区(径向压应力下降区)内的应力环越多,越清晰,围岩径向应力波动越剧烈,所达到的最大径向拉应力越大或最小径向压应力越小。

Numerical Simulation of the Influence of Unloading Time on the Cracking and Stress Wave Propagation in a Circular Tunnel Surrounding Rock

In this paper, the influence of unloading time (unloading rate) on the cracking, radial stress wave propagation, and radial stress evolution in a circular tunnel surrounding rock was studied by use of the continuum-discontinuum method proposed by the authors. This method was based on the Lagrangian element method, deformational discrete element method, and fictitious crack model. The influence of unloading time on the cracking, radial stress wave propagation, and radial stress evolution of the surrounding rock was investigated successively. A shorter unloading time was accompanied by more cracks, and a greater and more intense fluctuation of the maximum unbalanced force in the surrounding rock. The crack near the excavation boundary changed from a continuous distribution to a discontinuous distribution with the increase of the unloading time. When the unloading time was short, the crack distribution in the surrounding rock was continuous, which was because that the maximum principal stresses at these locations exceeded the tension strength. When the unloading time was moderate, the crack distribution in the surrounding rock was similar to V-shaped notches, which may be related to the presence of shear stresses at these locations. At a shorter unloading time, the number of radial stress rings in the disturbed zone (i.e., the decreasing zone of radial compressive stresses) was greater and clearer, the fluctuation of radial stresses in the surrounding rock was more evident, and the maximum radial tensile stresses (or minimum radial compressive stresses) were larger (respectively, smaller).