Application Research on Nondestructive Testing Technology for Quality of Anchor Based on Elastic Wave Reflection Method

Abstract:

Anchor technology has been widely used to reinforce slopes, underground caverns, deep excavations and the foundation of dams. It has attracted more and more attention of research worldwide on how to find a comfortable method to test the quality of anchoring systems.

According to the characteristics of anchor systems, we set up the kinetic equations and mathematical models, then solved the models using ANSYS / LS-DYNA program. We found that the simulated mathematical models perfectly match the experimental data. By changing one of the parameters or the input conditions in the model, we were able to understand the characteristic response of excitation energy, excitation length, structural defects, rock quality, and different data acquisition methods.

For short anchor systems (<10 m), we developed a method to extract the wave arrival times by obtaining the transient time domains instantaneously. It is well-known that obtaining the accurate wave arrival times from different structural interfaces within the anchor system is very difficult. But using our multi-parameter transient method, we could calculate the anchor length, the location of structural defect, and the grouting density. The obtained values were consistent with the actual experimental data. We also demonstrated that the kinetic energy of the collected waves from the bottom of the anchor had very close relationship with the grouting density and the position of the structural defects. For long anchors (> 60 m), mostly cable anchors, since little research could be followed, we started our research from designing the instrument, writing the program for data acquisition and analysis. We designed and developed novel sensors and preamplifiers. We used vertical stack technology to effectively enhance the weak signals from the deeper interfaces. In data processing, in addition to the traditional filter method, we also explored the current technology of signal processing such as true amplitude recovery and deconvolution, which enabled us to obtain improved signal to noise ratio and sensing precision. Through the above mentioned systematical studies, we developed a reliable nondestructive test method for both short and long anchors based on elastic wave reflection.

This research is funded by National Natural Science Foundation of China (Grant No. 41202223)