Mechanical responses and acoustic emission properties of bolting system under short encapsulation cyclic thrust tests

Research on bolt reactions under cyclic disturbance is still sparse due to complex and special laboratory processes. This paper endeavours to reveal the mechanical response and acoustic emission (AE) characteristics of bolts under cyclic loading, and a series of short encapsulated cyclic thrust tests (SECTTs) was conducted. First, the threshold determining stress level in the cyclic process was defined based on monotonic thrust tests, and the stress distribution along the steel tube was obtained simultaneously. Second, tests specified by staged cyclic loading with varied cyclic counts at each stage were conducted, and the influence of the cyclic count on the stability of the bolting system was evaluated. Third, tests specified by staged cyclic loading with holding intervals were conducted, and the creep behaviour of the bolting system was investigated. Controlling factors such as frequency, amplitude, and cyclic count were comprehensively considered. Fourth, two tests specified by staged cyclic loading with high cyclic count were conducted, and the influences of high cyclic count were discussed. Generally, a short encapsulated bolt undergoing cyclic loading behaved differently from a statically loaded bolt, and some interesting results were observed based on analysis of AE properties, strengthening effects, creep behaviour, failure prediction, bearing capacity evaluation, etc. At the end of this study, the reasonability and deviation of SECTT adopting steel tubes to simulate rock masses in the laboratory were discussed.