A Study On Mortar Plumpness Quality Of Rockbolt Anchorage Using Elastic Wave And Neural Network

Along with the development of the anchoring quality detection technology, detection methods are also emerging, which is the most widely used elastic wave method. The main advantage of the elastic wave method is fast, non-destructive, more accurately reflect the overall construction quality of bolt anchoring system. Although this method has been widely used, due to the lack of systematic theoretical study, resulting in many field test waveforms cannot be accurately interpreted. Theoretical studies currently bolt anchorage system of wave propagation are basically the anchor system as a one-dimensional rod to establish mathematical model, through the method of solving the one-dimensional wave equation to describe the problems of wave propagation in the anchoring system。There is no doubt that the theoretical work on wave propagation of anchorage quality system based on three dimensional condition is very important to the design and length of the test instrument of the anchor bolt and the seeking for the mortar plumpness.This paper is aimed at the problem of the lack of the theory research of elastic wave detection of bolt anchoring quality, carried out forward problem study of elastic wave propagation under the bolt anchoring system conditions. Through the numerical simulation of the finite difference of the three-dimensional elastic wave staggered grid, the theoretical calculation waveforms of different models are obtained. Analysis of the relationship between the relative amplitude of the reflection head wave and the mortar plumpness, and the influence of the parameters such as the strength of mortar, the length of reinforcement, the elastic modulus of surrounding rock and the frequency of elastic wave on the relative amplitude of the reflected head wave. The main influencing factors of the relative amplitude of the reflected head wave are determined accordingly. Using BP neural network to build relationship among the mortar plumpness, relative amplitude of the reflected head wave and influence factors, and quantitatively evaluate the bolt anchoring quality. The test results are compared with the actual model to verify the correctness of the method. It provides a new way for the determination of the plumpness of mortar, and it has important application value for the quality inspection of the anchorage engineering. This paper mainly does the following work and innovation:1. In this paper, a three-dimensional elastic wave staggered grid finite difference program is prepared, and the corresponding numerical simulation is carried out under the conditions of the surrounding rock, mortar and defects and other factors.2. According to the actual conditions, from the quarry custom limestone model and the proportion of 3:1 production of cement mortar to verify the correctness of the numerical model calculation.3. Fully matched layer absorbing boundary is arranged around the anchor structure, and the attenuation sine wave source is adopted. The model of different types of surrounding rock, different strength of cement mortar and cement mortar defects were simulated. According to the theoretical analysis and numerical simulation of the model instance, this paper concluded the wave velocity of surrounding rock and mortar will not affect the arrival time of the reflection wave at the bottom of the bolt, but its frequency will be reduced accordingly. The size of the mortar defects will affect the amplitude of the reflection wave at the bottom of the bolt. The larger the mortar defects, the larger the amplitude of the reflection wave at the bottom of the reinforcement.4. Using BP neural network to build relationship among the mortar saturation, relative amplitude of the reflected head wave and influence factors。The factors influencing the evaluation of the mortar plumpness were analyzed, and the input and output parameters of the BP neural network were determined。The mortar plumpness was predicted, and the predicted results were in good agreement with the measured values. This shows that the model has a high accuracy for the nondestructive testing of the mortar saturation of the bolt anchoring system. It has the value of popularizing and applying to meet the engineering requirement of anchor bolt detection.