In the present study, methodologies to evaluate damage around an underground opening due to seismic waves arising from mining-induced fault-slip are examined. First, expressions for an associated flow rule with a fail...In the present study, methodologies to evaluate damage around an underground opening due to seismic waves arising from mining-induced fault-slip are examined. First, expressions for an associated flow rule with a failure criterion are developed for biaxial stress conditions, which are implemented into FLAC3D code. A three-dimensional(3D) mine model encompassing a fault running parallel to a steeply dipping orebody is constructed, whereby static and dynamic analyses are performed to extract stopes and simulate fault-slip in dynamic condition, respectively. In the analysis, the developed biaxial model is applied to the stope wall. The fault-slip simulation is performed, considering shearing of fault surface asperities and resultant stress drop driving the fault-slip. Two methodologies to evaluate damage caused by seismic waves arising from the simulated fault-slip are examined:(i) the ratio of dynamic plastic strain increment to elastic strain limit and(ii) plastic strain energy density. For the former one, two types of strain increments are tested, namely effective shear strain increment and volumetric strain increment.The results indicate that volumetric strain increment is a suitable index for detecting damage near the stope wall, while effective shear strain increment is appropriate for evaluating damage in backfill. The evaluation method with plastic strain energy density is found to be capable of assessing damage accumulated in an extensive area caused by rock mass oscillation due to seismic wave propagation. Possible damage to mine developments in the proximity of a stope is clearly described with the index. The comparison of the two methods clarifies that the former one assesses "instantaneous" damage, which is found to be different from "accumulated" damage calculated using plastic strain energy density, in terms of damage area and its location. It is thus concluded that the combination of the two methodologies leads to more accurate damage assessment as a proper measure against rockburst.展开更多
Fault-slip taking place in underground mines occasionally causes severe damage to mine openings as a result of strong ground motion induced by seismic waves arising from fault-slip. It is indicated from previous studi...Fault-slip taking place in underground mines occasionally causes severe damage to mine openings as a result of strong ground motion induced by seismic waves arising from fault-slip. It is indicated from previous studies that intense seismic waves could be generated with the shock unloading of fault surface asperities during fault-slip. This study investigates the shock unloading with numerical simulation. A three-dimensional （3D） numerical model with idealized asperities is constructed with the help of discrete element code 3DEC. The idealization is conducted to particularly focus on simulating the shock unloading that previous numerical models, which replicate asperity degradation and crack development during the shear behavior of a joint surface in previous studies, fail to capture and simulate. With the numerical model, static and dynamic analyses are carried out to simulate unloading of asperities in the course of fault-slip. The results obtained from the dynamic analysis show that gradual stress release takes place around the center of the asperity tip at a rate of 45 MPa/ms for the base case, while an instantaneous stress release greater than 80 MPa occurs near the periphery of the asperity tip when the contact between the upper and lower asperities is lost. The instantaneous stress release becomes more intense in the vicinity of the asperity tip, causing tensile stress more than 20 MPa. It is deduced that the tensile stress could further increase if the numerical model is discretized more densely and analysis is carried out under stress conditions at a great depth. A model parametric study shows that in-situ stress state has a significant influence on the magnitude of the generated tensile stress. The results imply that the rapid stress release generating extremely high tensile stress on the asperity tip can cause intense seismic waves when it occurs at a great depth.展开更多
基金financially supported by a grant by the Natural Science and Engineering Research Council of Canada (NSERC) in partnership with Vale Ltd.-Sudbury Operations,Canada,under the Collaborative Research and Development Program
文摘In the present study, methodologies to evaluate damage around an underground opening due to seismic waves arising from mining-induced fault-slip are examined. First, expressions for an associated flow rule with a failure criterion are developed for biaxial stress conditions, which are implemented into FLAC3D code. A three-dimensional(3D) mine model encompassing a fault running parallel to a steeply dipping orebody is constructed, whereby static and dynamic analyses are performed to extract stopes and simulate fault-slip in dynamic condition, respectively. In the analysis, the developed biaxial model is applied to the stope wall. The fault-slip simulation is performed, considering shearing of fault surface asperities and resultant stress drop driving the fault-slip. Two methodologies to evaluate damage caused by seismic waves arising from the simulated fault-slip are examined:(i) the ratio of dynamic plastic strain increment to elastic strain limit and(ii) plastic strain energy density. For the former one, two types of strain increments are tested, namely effective shear strain increment and volumetric strain increment.The results indicate that volumetric strain increment is a suitable index for detecting damage near the stope wall, while effective shear strain increment is appropriate for evaluating damage in backfill. The evaluation method with plastic strain energy density is found to be capable of assessing damage accumulated in an extensive area caused by rock mass oscillation due to seismic wave propagation. Possible damage to mine developments in the proximity of a stope is clearly described with the index. The comparison of the two methods clarifies that the former one assesses "instantaneous" damage, which is found to be different from "accumulated" damage calculated using plastic strain energy density, in terms of damage area and its location. It is thus concluded that the combination of the two methodologies leads to more accurate damage assessment as a proper measure against rockburst.
基金financially supported by the Natural Science and Engineering Research Council of Canada(NSERC) in partnership with Vale Ltd.-Sudbury Operations,Canada,under the Collaborative Research and Development Program
文摘Fault-slip taking place in underground mines occasionally causes severe damage to mine openings as a result of strong ground motion induced by seismic waves arising from fault-slip. It is indicated from previous studies that intense seismic waves could be generated with the shock unloading of fault surface asperities during fault-slip. This study investigates the shock unloading with numerical simulation. A three-dimensional （3D） numerical model with idealized asperities is constructed with the help of discrete element code 3DEC. The idealization is conducted to particularly focus on simulating the shock unloading that previous numerical models, which replicate asperity degradation and crack development during the shear behavior of a joint surface in previous studies, fail to capture and simulate. With the numerical model, static and dynamic analyses are carried out to simulate unloading of asperities in the course of fault-slip. The results obtained from the dynamic analysis show that gradual stress release takes place around the center of the asperity tip at a rate of 45 MPa/ms for the base case, while an instantaneous stress release greater than 80 MPa occurs near the periphery of the asperity tip when the contact between the upper and lower asperities is lost. The instantaneous stress release becomes more intense in the vicinity of the asperity tip, causing tensile stress more than 20 MPa. It is deduced that the tensile stress could further increase if the numerical model is discretized more densely and analysis is carried out under stress conditions at a great depth. A model parametric study shows that in-situ stress state has a significant influence on the magnitude of the generated tensile stress. The results imply that the rapid stress release generating extremely high tensile stress on the asperity tip can cause intense seismic waves when it occurs at a great depth.
