Local Interfacial Damage Identification Of Grouted Rock Bolt Anchorage Based On Piezoceramic Wave Method

Grouted rock bolts are widely used in geotechnical engineering and underground structures.However,due to the influence of the factors such as bolt and anchorage material,geotechnical engineering conditions,construction technology and method,there are inevitably many defects in the construction and use of bolt anchorage system.These defects have a high degree of concealment,which will cause serious accidents and huge economic losses.Therefore,bolt detection is an essential part of the whole anchoring project.Only by improving the quality of bolt detection and the reliability of detection and evaluation results,can the quality and safety of the anchoring project be truly ensured.Therefore,the real-time,fast and non-destructive testing of anchorage quality has become an important issue to be solved.Piezoelectric ultrasonic guided wave technology is the key technology in the field of structural health monitoring(SHM).Piezoelectric ceramic is a kind of typical intelligent material,it has the characteristics of low cost,high sensitivity and easy to use,and is widely used in structural non-destructive testing(NDT).Based on the combination of theoretical analysis,laboratory test and numerical analysis,this paper studies the identification of local interface bond of grouted rock bolts,aiming at proposing a method of identification of local interface bond damage based on longitudinal piezoelectric ultrasonic guided wave echo reflection technology.The main research contents include:First of all,based on the existing theoretical research,the dispersion equation of ultrasonic guided wave in bare steel bar and anchor bolt anchoring system is derived,and the group velocity and phase velocity dispersion curves of guided wave are drawn with MATLAB software on the basis of known geometric parameters and material parameters;and the dispersion characteristics and propagation energy attenuation characteristics of ultrasonic guided wave in three-layer column structure are studied according to the dispersion curves,the appropriate guided wave excitation frequency is selected for indoor tests.Secondly,the indoor test system is designed,and the dispersion curve verification test and bolt mortar interface separation damage detection test are carried out.Through the experiment of the ring piezoelectric ceramic element to excite the ultrasonic guided wave of each frequency to the bare steel bar,the test value of the group velocity of the ultrasonic guided wave calculated by the time of flight method is consistent with the theoretical value,and the correctness of the dispersion curve is verified;then the ultrasonic guided wave with the excitation frequency of 50 k Hz is used to test the anchor bolt with different position damages,and the received guided wave signal chart is analyzed,and it is found that the energy of the echo signal of the longitudinal ultrasonic guided wave will be changed to some extent by the energy attenuation of the acoustic guided wave and the local interface bond damage.The farther the damage location is,the lower the energy of the damage echo is.Therefore,the damage reflection coefficient is introduced to quantitatively characterize the damage characteristics.Finally,the finite element software ABAQUS is used to simulate the healthy structure and components with different damage locations and different damage sizes,to verify and analyze the feasibility of the damage reflection coefficient to characterize the damage characteristics.The results show that the farther the surface damage location is,the smaller the damage reflection coefficient is,the greater the damage reflection coefficient is.