Yujie Zhu

A critically stressed fracture will slide in response to the increase in fluid pressure inside the fracture while impounding, which will trigger induced seismicity. The mechanism of fluid overpressure is regarded as a significant factor in the reaction of the fracture slip after water diffusing. This study uses a shearing test with a cylinder of granite, with 100 mm height and 50 mm diameter, under the condition of hydraulic-mechanic (HM) coupling to figure out how fluid overpressure alters the mechanical behavior of the critically stressed fracture. The cyclic water pressurization simulates periodical impounding in the water reservoir. Results show that several slip events happen when water pressure continues to rise higher than the stable state. The change of roughness also indicates the deterioration of the fracture surface while sliding. According to the results, we conclude that the difference between inlet pressure and outlet pressure leads to an overpressure of the fracture, promoting a series of slips and induced seismicity. Hydraulic energy is introduced to explain the relationship between the input and output energy, which is also strong evidence to illustrate that fluid overpressure is a crucial mechanism in reservoir-induced seismicity.

We used the hyperbolic Drucker–Prager and damage-failure models to simulate a three-dimensional rock fragmentation with a tunnel boring machine (TBM) disc cutter through ABAQUS. The energy entropy method was proposed to identify the optimal disc cutter spacing. In order to verify the results of the numerical simulation, previous linear cutting machine (LCM) test data were referred to. The results of the numerical simulation were verified by comparing the mean rolling force and the specific energy against the corresponding values from the LCM tests. The proposed energy entropy method showed a good agreement with the LCM test results, thus proving its usefulness in analyzing rock fragmentation for various disc cutter spacings. The comparison between energy entropy and the specific energy showed that both methods provide similar conclusions with regard to optimal spacing. The results of this research showed that energy entropy can predict the performance of TBM disc cutters and could help improve their design.

Disc cutters are the dominant tool used in the excavation of hard rock formations in any underground construction application, such as when tunneling using tunnel-boring machines (TBM), as well as in shaft- and raise boring operations. Optimization of the cutting geometry of a given disc cutter for application in a rock formation often involves full-scale cutting tests, which is a difficult and costly proposition. An alternative to full-scale testing is the numerical simulation of TBM disc cutters for optimization under different settings. Recent efforts in the field of numerical simulations of rock cutting have shown the relative success of discrete element models, such as particle flow code (PFC), to simulate two- and three-dimensional rock fragmentation. This study is focused on a sensitivity analysis of PFC simulation of rock-cutting relative to the size of the elements. The calculated cutting forces were compared with the recorded forces under various conditions during full-scale tests using a linear cutting machine (LCM) on Colorado red granite (CRG). The estimated cutting coefficient and specific energy in the LCM tests and simulations showed good correlations, which validates the numerical simulation results. Two- and three-dimensional models showed that two-dimensional numerical models can offer a qualitative assessment of crack development, whereas three-dimensional models could be used to estimate the specific energy when cutting. The results can help in predicting the cutting forces in different rocks and ultimately improving disc-cutter geometry and cutter-head design.