扭转导波在锚固锚杆中传播的数值模拟

Numerical simulation of torsional guided wave propagation in grouted rock bolt

采用有限元数值模拟的方法研究了扭转导波在锚固锚杆中的传播性质。建立了自由锚杆和锚固锚杆的有限元模型,在锚杆顶端激发20～60 kHz扭转导波信号,计算得到导波在自由锚杆和锚杆锚固段的传播速度值与理论值吻合很好,证明了扭转导波数值模拟方法的有效性。数值模拟结果表明:随着激发波频率的增大,扭转导波在自由锚杆和锚杆锚固段中的衰减值均呈线性递增趋势,导波在锚杆锚固段上界面的反射回波逐渐减弱;扭转导波在锚杆锚固段的衰减值较大,无法在锚杆顶端采集到锚杆底端反射回波信号,所以扭转导波不适用于锚杆长度的检测;随着锚固介质弹性模量的增大,同一频率扭转导波在锚杆锚固段上界面的反射波逐渐增强。通过检测扭转导波在锚杆锚固段上界面的反射回波,可以确定锚固介质弹性模量的大小。

Numerical simulation was conducted to study the propagation properties of torsional guided wave in grouted rock bolts. Finite element models of a free bolt and a grouted bolt were established; and torsional guided waves with frequencies of 20-60 kHz were excited at the top of the bolts. The numerical results of guided wave velocities in the free bolt and in the anchoring section of the bolt agree well with the theoretical results. The result proves that the finite element method is an effective way to simulate torsional guided wave propagation in grouted rock bolts. The results of numerical simulation show that both the attenuation values of torsional guided waves in the free bolt and in the anchoring section of the bolt increase linearly with the increase of excited wave frequency. Meanwhile, the reflection amplitude of guided waves from the upper interface of the grouted rock bolt decreases. Torsional guided waves attenuate greatly in the anchoring section of the bolt; and reflected waves from the embedded end of bolt are not able to be captured; as a result, torsional guided waves are not applicable for bolt length testing. When the elastic modulus of grout material increases, the amplitude of upper interface reflected wave increases; so the upper interface reflected wave can be used to evaluate the elastic modulus of grout material.