Papers by Keyword: Volumetric Strain

Abstract: Controlling the stability of surrounding rocks in underground excavations during in-depth resource development must be confronted with post-peak deformation and failure problems of jointed rock masses. This paper describes routine triaxial compression testing on standard cylinder specimen with persistent joints in different inclinations and under different confining pressures, and analyzes deformation characteristics of rock masses with persistent joints in different inclinations and under different confining pressures. Test results show that the peak strength, residual strength, and peak strain of the jointed specimen basically increase with increasing confining pressures but decrease with increasing joint inclinations. Test results well reflect that it is incorrect to evaluate deformation characteristics of jointed rock masses with continuum mechanics and research results provide a reference for the research on the stability of surrounding rocks in underground excavations.

Abstract: By means of MTS electro-hydraulic servo system, specimens from deep coal mine rock are conducted the permeability characteristics experiment under the condition of the stress-strain process and high pore-water pressure, also the results show that both the permeability rate and volumetric strain curves are V shaped, which link the dynamic changes of the microscopic fracture porosity and corresponds with the stress-strain. Meanwhile, under certain external conditions, whether the change of the pore-water pressure can improve the permeability properties or not, it depends on the critical threshold, moreover, the permeability properties under pore-water pressure higher than critical threshold have been improved several times than that at low pore-water pressure, and the peak of strain-permeability rate has a corresponding change with the peak of stress-strain curve, which shows a hysteretic characteristic. The higher the pore-water pressure is, the lower peak strength is needed, the more distinctive effects of dilatation emerge, and the more strain is needed for the appearance of permeability peak, This article provides the basis for the employment of high pore-water pressure to improve the permeability and disaster prevention of coal rock water injection.

Abstract: The physical processes triggering the fluid flow within the stressed rock are highly complex and not fully understood. The granite sample obtained from Creighton mine, Canada, was subjected to the temperature-pressure effects using a special rock mechanic testing machine equipped with a high precision gas monitor. It is shown that when the sample approached to the peak stress during the uniaxial compression test, the connective cracks instantaneously occurred accompanied by a swarm of AE activities, which suddenly decrease the fluid pore pressure. This change can be able to drive the gas back to the newly emerging crack due to the formation of gas pressure gradient within the damage zones. It is indicated that the different permeabilities among the zones can dominate the suction-exhaust proceeding of pore fluids within rock mass. Beyond the volumetric strain at null, the deformation of the stressed rock leads to a reversely change in pore pressure of closed pores. The feature for the gas emission determined by the changes in pore structure of rock is also discussed and analyzed.

Abstract: A complete stress-strain experiment curve, gained through exerting low confining pressure on brittle rock, reflects the deformation and destruction process of rock under different confining pressure, and reveals that after the destruction of rock, not only slip deformation but also re-destruction process will take place, which would possibly lead to further reduction of the mechanical properties of the rock mass. Through the analysis of the relation between complex failure modes, load carrying capacity after rock destruction and the volumetric strain, the paper gives us a further explanation of the complex destructive process of rock. The basis for the rock’s load-carrying capacity after destruction is an effective restraint stress, which shows that effective supporting in underground engineering is the key factor for providing the cracked surrounding rock with load-carrying capacity and guaranteeing the stability of the structure.