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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。
The propagation properties of torsion guided waves in anchorage bolts were studied by means of finite element numerical simulation. The finite element model of free rock bolt and anchor bolt was established. The torsional guided wave of 20-60 kHz was excited at the top of rock bolt, and the calculated value of the guided wave in the anchored part of free rock bolt and rock bolt was consistent with the theoretical value Well, the validity of the torsion guided wave numerical simulation method is proved. Numerical simulation results show that as the frequency of the excitation wave increases, the attenuation of the torsion guided wave in the free rock bolt and the anchorage section of the rock bolt increases linearly. The reflection echo of the guided wave on the upper anchorage section of the rock bolt gradually increases The torsion guided wave is not suitable for the detection of the length of the anchor rod. With the elasticity of the anchorage medium When the modulus increases, the reflected wave of the same frequency torsional guided wave on the interface of the anchorage section of the anchor gradually increases. The elastic modulus of the anchoring medium can be determined by detecting the reflected echoes of the torsion guided wave at the interface of the anchorage section of the anchor.