Dynamic performance of energy-absorbing rockbolts based on laboratory test results. Part Ⅱ: Role of inherent features on dynamic performance of rockbolts

摘要

Deep mining and the related dynamic loading are the critical challenges confronting the reinforcement system like energy-absorbing rockbolts, which plays a decisive role in the dynamic response of underground mine excavations. Over the past decades, various types of novel energy-absorbing rockbolts with different deformation mechanisms and dynamic characteristics have been invented. Meanwhile, the test methods and facilities to quantify the dynamic performance of rockbolts have been proposed, and a lot of test results are obtained. In the companion Part II, with comparative analysis of test results along with available data from literature, some inherent features related to the dynamic performance of bolts have been revealed. The research indicates that, for both shank stretching and ploughing/extrusion bolts, the energy absorption is approximately proportional to the displacement. For the shank stretching bolts, only when the impact energy is higher than a threshold value, yield and strain hardening occurs; in the case of strain hardening, even a low impact energy can roughly predict the dynamic response curve. The statistical analysis of test results indicates that, in laboratory dynamic tests, the strain rate of bolts varies between 0.5/s and 3/s, and the increments of dynamic capacity enhancement factor (DCEF) is 3.4%-10.5%. For a particular bolt, DCEF can be roughly viewed as a constant which is mainly dependent on the yield strength level of the shank. Therefore, dynamic impact load can be approximated as a constant; the dynamic load-displacement curve can be simplified into a unique polyline segment comprising two line segments; and the impact duration is linearly related to the input momentum. These findings could be used for the pre-evaluation of the dynamic performance of the candidate bolts before laboratory test and support scheme design.