A Study On Nondestructive Detection Of Stress Wave In Anchorage Bolts And Evaluation Of Anchorage System Quality

Rock bolt has been proved a useful means of anchorage technology and is often used to reinforce rock mass in many fields of Geotechnical engineering such as drift convergency, tunnel, underground cavity, foundation pit, slope and so on. Deficiency in anchor bar is very dangerous .It may bring inestimable loss. To avoid this, a reliable testing way is needed. So the research of testing way of anchorage system is a necessary and stringent task.However, the traditional testing way of static load can not meet the requirement of wide scope testing for anchor bars in practice, using stress wave in the inspection of construction quality of bolting is a non-destructive testing .This thesis is based on the theory of stress wave and composite material, main conclusions are as follows:(1) By means of theory analysis, transmission characteristic of stress wave in bolt and surrounding media is studied. Propagation laws of stress wave in bolt, rock medium and coupling system are researched. Attenuation rule and propagation law of elastic wave in anchorage system are obtained. These results provide some important theory basis for bolt anchorage quality testing.(2) Bolt and mortar in anchorage system are approximatively viewed isotropic objects. Applying composite material theory, equivalent one-dimensional model is founded.(3) Based on one-dimensional wave theory, the propagation equation of stress wave in anchorage system is induced. Given the boundary conditions and initial conditions, the dynamic response is solved, and the influence of many parameters including wave velocity, basic frequency, damp coefficient, etc. is analyzed.(4) The numerical simulation of flaws in anchorage system is carried out. Through adjusting the coefficients of dominant equation, the dynamic response of defective anchorage system can be simulated with difference method, and simulative response is satisfied with actual response. According to the propagation laws of stress wave, the parameters such as wave velocity, basic frequency and damp coefficient,are determined to evaluate the anchorage quality.(5) Through comparing and analyzing, it's shown that the simulated curves are in good agreement with the waveshapes obtained from field measurements. Consequently, the models, the parameters and the results of numerical simulation in this paper are proved to be correct and effective.(6)A method in which BP neural network is combined with the genetic algorithm to optimize structural problem is presented. The method uses the ability of associative memory to predict the bar's limiting bearing capacity and integrity and to evaluate anchorage system quality.This thesis also provides theoretic foundation for reference for the application of ultrasonic detection technology in construction process of slope engineering, underground engineering and in follow-up management process of ultrasonic monitoring, stability evaluation, rock intensity predication and terrestrial stress measurement.