Hengjie Luan

Study on Macro–Meso Failure Mechanism of Pre-fractured Rock Specimens Under Uniaxial Compression

There are many fractures in natural rock mass which have a significant influence on the stability of rock engineering. Rock is a kind of aggregate made up of various particles, the research on the meso level can fundamentally reveal the failure mechanism. In order to comprehensively research the effect mechanism of fractures on the failure characteristics of fractured rock, uniaxial compression numerical experiments were conducted based on discrete element method. The macroscopic and mesoscopic mechanical response of pre-fractured rock specimens with varying fracture length and dip angle were studied. The evolution process of macroscopic and mesoscopic physical quantities was obtained. The results show that the macroscopic failure process of fractured rock was an evolution process of rock from the microscopic level to macroscopic level that resulted from the interaction of internal particles under compression loading. In this process, the energy dissipation was also evolving. There was an obvious relativity between the particle rotation radian region-related feature and the distribution location and number features of cracks. The distribution pattern of prefabricated fractures had a great influence on the failure mode and plays an important role in the macroscopic characteristics and the evolution of internal components of pre-fractured rock specimens. Research result is full of important theory significance and engineering value to evaluate the stability of rock engineering.

Assessment of Bolt Reinforcement Effect Based on Analytic Hierarchy Process

The prediction and assessment of bolt reinforcement effect are directly related to the safety of the underground engineering. However, the bolt support effect is affected by multi-factors. In order to evaluate the reinforcement effect comprehensively, the weight of the controlling factors of the reinforcement effect was carried out based on analytic hierarchy process (AHP). The feasibility of the AHP model was verified by numerical simulation. The study indicated that the weight of controlling factors from large to small is: rock grade, geology, bolt diameter, number of bolts, excavation time, rock formation, anchoring length, bolt length, technical equipment, bolt type and construction worker. In addition, two-stage assessment and management methods for bolt reinforcement were proposed, including the preliminary assessment and dynamic controlling assessment. Preliminary assessment is the evaluation of risk surroundings, and it is a risk assessment carried out before the construction scheme. Dynamic assessment is the evaluation of risk surroundings, risk factors and reinforcement background, and it is brought into operation for dynamic risk assessment and management. Moreover, the influence of bolt parameters to reinforcement effect was deeply analyzed. The results show that the diameter of bolts should be controlled within 30xa0mm, and the length of bolts should be limited within 6xa0m. Furthermore, the existence of free part along a bolt could improve the reinforcement effect. This research has an important theoretical reference to guide the parameter design of bolt support engineering.