Application of Impact-Echo Method for Rockbolt Length Detection

This study examines the spectral responses resulting from the use of the impact-echo method for rockbolt length detection. A rockbolt is a thin long member that is often used in tunnels or slope protection works to fasten structures and soil/rock mass tightly together. It involves embedding a long steel bolt fully anchored to the original structure to resist strong pulling forces and stabilize the original structure or serve as a connecting member between two materials. Inadequate embedment length or poor grouting can prevent rockbolts from serving the function they were designed for and result in rockbolt failure. This study employed finite element analysis to conduct numerical simulation analyses of the stress wave signals in rockbolts and then used the impact-echo method to measure rockbolt length and grout integrity. Our results indicate that the impact-echo method can be used to determine rockbolt length but requires prior knowledge of whether the rockbolt is grouted. If not, then its detection signals will be similar to those of a bare steel bar. The rockbolt length can then be calculated using the theoretical wave velocity in a steel bar and the fundamental frequency derived from measurements. If the rockbolt is grouted, then the wave velocity in the grout material must be known so that the accurate length of the rockbolt can be derived.

本研究探讨了采用冲击回波法检测锚杆长度的光谱响应。锚杆是一种常用于隧道或边坡防护工程中，用以紧固结构及土壤/岩体，防止其分离的细长部件。锚杆的安装涉及将一根长钢螺栓完全锚固于原有结构中，以抵抗强大的拉力并稳定原有结构，或作为两种材料之间的连接件。锚杆嵌入长度不足或灌浆质量不佳将导致锚杆无法发挥其设计功能，并可能导致锚杆失效。本研究通过有限元分析对锚杆中的应力波信号进行数值模拟分析，随后采用冲击回波法测量锚杆长度和灌浆完整性。研究结果指出，冲击回波法可用于确定锚杆长度，但需事先了解锚杆是否灌浆。若未灌浆，其检测信号将与裸钢杆相似。随后，可利用钢杆中的理论波速和由测量得到的基频来计算锚杆长度。若锚杆已灌浆，则需了解灌浆材料的波速，以便准确计算出锚杆的长度。