Investigation On Principle And Method Of The Nondestructive Testing Of Anchorage Defects In Partial-Cohesive Bolts

Bolt support is the major form of coal mine roadway support. Anchorage defect is one of the important factors which affect the quality of bolt support. To detect bolt anchorage defects quickly and effectively is significant to reinforcing the roadway support promptly and ensuring the safe and efficient production of the coal mine. Based on the stress wave theory and testing technology, nondestructive testing principle and method of anchorage defect of coal mine partial-cohesive bolt were systematically studied in this paper. The following innovative results are obtained:(1) The mechanical model of a partial-cohesive bolt with anchorage defects was established. The corresponding wave equation and its analytical solution were obtained. The influence of mechanical properties of the anchored surrounding rock on the stress wave propagation in coal mine bolt were investigated systematically. It was found that the elastic and viscous properties of anchoring medium can cause the dispersion of stress wave velocity. This revealed the physical mechanism of stress wave propagation in the bolt support of coal mine.(2) We designed the nondestructive testing system of the bolt anchorage quality, established the physical model of stress wave nondestructive testing of the partial-cohesive bolt with anchorage defects, and systematically investigated the influence of size and distribution characteristics of anchorage defects on dynamic nondestructive testing signals of bolt, and then obtained the pattern of energy dissipation characteristics of stress wave propagation in bolt changing with the anchorage defects.(3) Based on the analysis of the characteristics of the stress wave signal obtained from the numerical simulation and experimental detection, the characteristic quantity of the degree of anchoring defect, or reflected energy ratio(re), was introduced. The relationship between re and the energy of reflected signal of anchor initial end and anchor end was presented. The corresponding relationship between the anchorage length and re was obtained. Further proposed is the estimation method of the ultimate anchor force in the defective anchorage system.(4) By using the multiscale entropy method, the effect of defect distribution on the nondestructive testing signals of anchorage quality was analyzed. The pattern of characteristic quantity of signal complexity(PRSS) varying with the position of anchorage defect was obtained. The mechanism of the influence of the anchorage defect position distribution on the ultimate anchor force was given. Upon the introduction of the influence factor ηs, the estimation method of the ultimate anchor force of the defective anchorage system was effectively modified.(5) On analyzing the nondestructive testing signal of the bolt anchorage defect with anchor plate, we proposed the collaborative analysis method based on the empirical mode decomposition method combined with the multiscale entropy method, and solved the problem that the anchor plate would lead to the deviation of the analysis results when applying the multiscale entropy method to analyzing the nondestructive testing signal of the bolt anchorage defect with the anchor plate. Based on the empirical mode decomposition and the multi-scale entropy analysis method, the multiscale entropy evaluation system of bolt anchorage quality was designed, so that the intelligence and visualization of the signal processing were achieved, making the evaluation system easy to use in engineering practice.The research results of this dissertation not only help to evaluate bolt anchorage quality accurately and objectively, but also have positive significance to the safety in production and improvement of production efficiency of coal mine.