周期冲击载荷在采矿、土木等工程中较为常见。在周期冲击荷载作用下，巷道围岩会在极短时间内产生大量裂缝，块体会以猛烈方式脱离巷道围岩，造成岩爆、垮塌等灾害。自主开发的拉格朗日元和离散元耦合的连续-非连续方法主要包括4个计算模块：应力应变模块、节点分离模块、接触力求解模块和运动方程求解模块。鉴于单元畸变和局部自适应阻尼可能导致单元弹射出模型时速度失真，为了准确模拟弹射现象，在该连续-非连续方法的基础上，对弹射单元进行了刚化处理。该方法的实质是确保弹射单元在碰撞前后作刚体运动，这是通过对节点速度取平均、消除单元应力实现的。对周期冲击载荷作用下巷道围岩的变形—开裂—运动过程进行了模拟。模型尺寸为40 m×40 m，被剖分成160×160个正方形单元，巷道尺寸为6 m×6 m。模型的左、右侧面均为透射边界，即应力波经过时不会发生反射。通过在巷道顶板布置多个测点，获取了最大主应力在整个模拟过程中的演化规律。该过程包括巷道开挖前模型的平衡过程、巷道开挖后模型的平衡过程及应力波在模型中传播过程。研究发现，当应力波在模型中传播时，弹射单元任一节点的水平速度呈现上升—稳定—衰减的变化过程，这与不进行刚化处理的结果相比更符合实际；巷道顶板左、右对称线上大部分测点的最大主应力呈现近似正弦波动上升—衰减—稳定的变化过程。在某一节点分离前，最大主应力首先呈现有规律的波动；然后，波动幅度突然增大，并伴随着剧烈震荡。阐明了顶板的拉裂机理：当应力波传入模型之后，顶板某一位置的最大主应力的波峰和波谷随着时间的增加呈增加的趋势，反射的多个拉应力波的累积作用不断提升该位置最大主应力的波峰，致使拉裂。另外，还初步分析了周期冲击载荷频率对单元弹射初速度和剪、拉裂缝区段数目的影响。分析发现，随着频率的增加，脱离巷道围岩的单元的平均弹射初速度增加，剪、拉裂缝区段数目减小。

Periodic impact loads are common in mining and civil engineering. The roadway surrounding rock will produce a large number of cracks in a very short time under periodic impact loads, and rock blocks will be ejected from the roadway surrounding rock in a violent way, causing rockbursts and collapses, etc. The continu um discontinuum method has been developed, which the Lagrangian element method and the discrete element method are combined. The method includes four modules: the stress strain module, the nodal separation module, the solving contact force module and the solving motion equation module. The element distortion and local adaptive damping may lead to inaccurate velocities for ejected elements from a model. To accurately model the phenomenon, the ejected elements are treated as rigid bodies based on the continuum discontinuum method. The present treatment can ensure the rigid body movement of the ejected element without contact, which is achieved by averaging the velocities of nodes and eliminating the stresses of elements. The deformation cracking movement process of the roadway surrounding rock under periodic impact loads is modeled. The size of the model is 40 m×40 m. The model is divided into 160×160 square elements, and the size of the roadway is 6 m×6 m. The left and right sides of the model are transmitting boundaries so that no reflection occurs when the stress wave passes through. A few monitored points are arranged at the roadway roof, and the evolution of their maximum principal stresses in the whole calculation process is presented. The process includes the balanced process of the model before excavation, the balanced process of the model after excavation and the propagation process of stress wave in the model. The following results are obtained. When the stress wave propagates in the model, the horizontal velocities of nodes of ejected elements exhibit an increase, followed by a constant and then a decay. This is more practical than the result that the ejected elements are not treated as rigid bodies, and the maximum principal stresses of most monitored points at the symmetric line between the left and right parts of the roadway roof exhibit an approximately fluctuating increase, followed by a decay until a constant is reached. Before a node separate, the maximum principal stress regularly fluctuates, followed by a sudden and violent fluctuation with a large amplitude. The mechanism of roof cracking is expounded. After the stress wave is introduced into the model, the peaks and troughs of maximum principal stresses at the positions of roof increase with time, and the accumulation of several reflected tensile stress waves continuously elevates the peaks of maximum principal stresses at positions, resulting in cracking. In addition, the effects of frequency on the initial ejected velocity and the number of shear and tensile crack segments are preliminarily analyzed. With an increase of frequency, the averaged initial ejected velocity of each element ejected from the roadway surrounding rock increases, and the number of shear and tensile crack segments decreases.

1 连续-非连续方法简介

   1.1 原始方法简介

   1.2 脱离模型的单元作刚体平动的必要性及处理方法

2 计算模型及方案

3 计算结果及分析

   3.1 周期冲击载荷作用下巷道围岩变形-开裂-运动过程

4 结论