Search

To reflect the effect of confining pressure on the brittleness of the post-peak rock, the degradation angle of post-peak strength of the new parameter was presented. Based on the test data for mudstone of Shanxi in triaxial compression, the linear relationship between the degradation angle and the confining stress was founded. The law between the equivalent plastic shear strain and the degradation angle was presented, and the strain softening model of rock based on the degradation angle was set up. Fish function method within FLAC was used and the numerical code was developed. In numerical case study, the strain softening processes under variable confining pressure for mudstone of Shanxi were modeled. The simulating results accord with experimental data. Those show that the degradation angle is an effective parameter to reflect the effect of confining pressure on the brittleness of the post-peak rock; the model in this paper is reasonable and can be used to model the strain softening processes of post-peak strength rock. [ABSTRACT FROM AUTHOR]

To reflect the permeability change of loaded rock, the relationship between the permeability and stress-strain curve of rock was analyzed, and the process the deformation and failure of rock was supposed to be elastic, brittle and plastic. Based on the process the permeability evolution model for rock was presented. In this model the evolution of the permeability for the rock element include; (1) The permeability can be expressed by porosity during elastic deformation phase. (2) In the post-peak stage a shear failure rock element may be represented hydraulically as a unit of rock containing two oblique crossing conjugate fractures. (3) In the post-peak stage a tension failure rock element may be represented hydraulically as a unit of rock containing two orthogonal fractures. Then based on so-called cubic law between smooth parallel plates the permeability evolution model during dilation was presented. In the model the dilation effects of failed element on permeability was considered. Fish function method was adopted to implement the model in FLAC software. The permeability evolution process of a cubic loading rock sample under varied confined stress was simulated. The results show that the model can better reflect the permeability evolution due to elastic deformation or failure. Besides the effect of confined stress on permeability can also be better expressed. [ABSTRACT FROM AUTHOR]

The standard coal briquette specimens from Huaxing Mine, in Jilin, were made. The permeability test was performed in ZYS-1 equipment for the measurement of permeability to study the effects of confining stress, axial stress and temperature on permeability of coal briquette specimens. The results show that with the increasing confined stress, the permeability of coal briquette specimen decreases. The permeability of coal is greatly effected by differential stress. Under the condition of confined stress, with increasing differential stress (axial stress) the permeability of the specimen decreases due to the elastic contraction. When the specimen failed due to increasing differential stress their porosity volumes increase due to dilation, and the permeability also increases. Therefore the permeability of samples takes on "V" curve under low confined stress. However the permeability decreases under high confining stress. The flow of methane in coal is greatly effected by temperature. When the temperature increases, on one hand the kinematic viscosity of methane increases. On the other hand the grains of coal swell and lead to contraction of flow space and reduction of permeability. [ABSTRACT FROM AUTHOR]