基于剪切边界的隧道系统锚杆剪力特征离散元数值模拟研究

Discrete Element Numerical Simulation Study on Shear Characteristics of Tunnel Systematic Bolts Based on Shear Boundary

采用块体离散元数值模拟方法,构造出锚杆受剪的边界条件,对隧道系统锚杆剪力的断面分布特征及演化规律开展了数值模拟研究,并探讨了围岩破碎程度、锚杆布置形式等因素对锚杆剪力的影响。结果表明:(1)隧道系统锚杆的剪力与节理剪切位移正相关,锚杆的剪切效应发生于破碎岩体中,在完整岩体中可以被忽略;(2)锚杆剪力总是低于相同位置的轴力,但剪轴比最大可接近75%;(3)在锚杆施作初期,锚杆剪力会因施作部位、锚杆到隧道内轮廓表面距离的不同存在较为显著的差异,施作初期的锚杆剪力峰值可能高于长期稳定值;(4)破碎岩体中的破碎岩块体积越大,或破碎范围越广,锚杆的剪力也越大;(5)系统锚杆越长,越容易受到剪切作用,密集的锚杆布置有助于减小系统锚杆承受的剪力。

By using the block discrete element numerical simulation method and creating the boundary conditions of bolt shearing,the numerical simulation study on the sectional distribution characteristics and evolution law of shear of tunnel systematic bolts has been conducted,and how the factors such as surrounding rock fracture degree and bolts layout pattern will affect the bolt shear has been investigated.The study results are stated as follows:(1)The shear of the tunnel systematic bolts and joint shear displacement are in positive correlation,and the shearing effect of bolt happens in broken rock mass and is negligible in intact rock mass;(2)The bolt shear is always less than the axial force at the same position,but the maximum shear-axial force ratio is close to 75%;(3)In the initial stage of bolt installation,the bolt shear will differ considerably due to the installation position and the distance between bolt and inner contour surface of tunnel,and the bolt shear peak in the initial stage of installation may be higher than the long-term stable value;(4)Greater broken rock volume or greater breaking range in the broken rock mass means greater bolt shear;(5)Longer bolts are more susceptible to shear,and densely placed bolts can help reduce the shear sustained by the systematic bolts.