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The creep of rock is a slow stress adjustment deformation and an evolutional process of rock mass destruction. Therefore, rock creep plays a vital role in a variety of rock engineering. To reveal the creep properties of rock, the following work has been done. A series of triaxial creep tests has been conducted considering different low confining pressures. The creep curve is analyzed under different confining pressures, and the creep law of each stage is obtained. Many results were obtained for the influence of confining pressure on the instantaneous modulus of deformation, creep strain, creep rate and instantaneous strain. The proportion of the various stages of creep changes under different confining pressure. Due to the existence of confining pressure, the ultimate failure method of rock has also been affected. Creep data can then be fitted by the improved Nishihara model, revealing a good relationship. The conclusion of this paper can provide some significant guidance for rock engineering. [ABSTRACT FROM AUTHOR]

To ensure the safe and effective application of deep geotechnical engineering, it is necessary to establish a suitable constitutive model of the rocks in thermal environment, including geothermal energy mining, and deep geological treatment of nuclear waste and tunnel fire. A strain-softening damage model of the rocks with defect growth is established based on damage evolution. According to the change in the tangent modulus from the compression phase to the elastic stage, we established a constitutive model reflecting the nonlinearity characteristics of the compression phase. According to the change in the energy conversion, the energy consumption coefficient is introduced to describe the deformation characteristics of the rocks when the residual stress is reached. The specific physical meaning and the calculation method of the energy consumption coefficient are given to correct the shortcomings of the evolution of the damage variable. We then analyzed the relationship between parameters in the constitutive model of the rocks at high temperature and normal temperature. Based on the constitutive model of the rocks at normal temperature, we established a constitutive model reflecting the influence of high temperature. Finally, the established model fit the stress-strain curves of several kinds of the rocks at different temperatures and generated desired results. The established model can be used to describe the stress-strain curve characteristics of the rocks at different temperatures. [ABSTRACT FROM AUTHOR]

The excavation of the rock mass will have a great influence on the characteristics of the caverns under extremely bad geological conditions. According to the characteristics of the engineering geology, several groups of the caverns are designed to be excavated in the rock mass with three sets of through joints. Based on the summary of the failure mechanism and the failure pattern, the classification method of the failure modes is done for the flat large-span underground cavern with three sets of through joints. The classification method takes into account the control factors of the surrounding rock instability, failure mechanism, distribution of the disturbed zone, and characteristics of the rock weakness, etc. The failure modes of the flat large-span caverns contain six types: the relatively stable, the partial area falling, and the partial collapse of vault, the zigzag failure of rock stratum, the V-shaped failure, and the large-scale collapse. The change law of the vertical stress is first increasing and then decreasing for the surrounding rock in the disturbed zone. The horizontal stress shows an exponential change trend with an increase in the distance from the vault. Influenced by the failure degree of the caverns, the change law of the vertical displacement for the vault can be divided into two types. The horizontal displacement decreases with an increase in the distance from the sidewall, and there is an exponential relationship between them. [ABSTRACT FROM AUTHOR]

To reflect the influence of saturation effect, an improved strain-softening damage model is established to link the saturated rocks with the dry rocks. First, the original damage model is improved to describe the characteristics of each stage in the uniaxial compression. According to the change of the tangent modulus from the compression phase to the elastic stage, an improved strain-softening constitutive model reflecting the nonlinear change characteristics of the compression phase is established. According to the change of the energy during the uniaxial compression, the energy consumption coefficient (λ) is introduced to replace the damage ratio coefficient to describe the deformation characteristics of the rocks when the residual stress or failure is reached. The specific physical meaning and calculation method of the energy consumption coefficient are given to correct the shortcomings of the damage evolution in the original model. Then, the relationship between the parameters in the new model for the dry rocks and the saturated rocks is analyzed. Based on the constitutive model of the dry rocks, a new constitutive model which can reflect the influence of the water-weakening is established. Finally, the stress–strain curves of different rocks are fitted by the established model, and good results are obtained. The physical meaning of each parameter in the model is clear, and each parameter can be obtained by the test results. The improved constitutive model can be applicable to both the dry rocks and the saturated rocks. [ABSTRACT FROM AUTHOR]

The mechanical properties of rocks are greatly affected by water action. Many underground structures can be failed by changes in the water environment. To reveal the mechanical properties of the rocks after saturation, a series of saturated sandstones are prepared to study the changes in the mechanical properties during post-peak cyclic loading and unloading. The results show that the strength characteristics of the sandstones decrease after saturation. There is an exponential function between the peak strength and the damage degree and between the crack damage stress and the damage degree. A new method for calculating the elastic modulus is proposed. The results of both calculation methods show that the elastic modulus of the saturated sandstones decreases. The relationship between the elastic modulus obtained by the two methods and the damage degree is quite different. After saturation, the dilatancy of the sandstones increases in the post-peak stage. The volumetric strain, the plastic shear strain, and the peak dilatancy angle all increase with increasing damage degree. Because of the filling by water molecules, the P-wave velocity increases. There is an exponential function relationship between the P-wave velocity and the damage degree. Because of the softening after saturation, more macroscopic failure cracks and fracture surfaces will be formed in the saturated sandstones. The research results of this paper can provide some guidance for excavation and engineering design in water-rich rock. [ABSTRACT FROM AUTHOR]

Briefly introduced the simple shear apparatus under high stress that was developed from RMT. A series simple shear tests under high stress show that the relation curve between shear stress and tangential displacement under high normal stress is different from the hyperbolic curve in direct shear tests, and the complete deformation process of interface under high stress can be described as nonlinear elastic-perfect plastic(NEPP). According to some characteristics of the fitting curve, the deficiency of the NEPP was pointed out. The mathematic “half value index” was used to illustrate that Weibull distribution with three parameters (WNEPP) can overcome the mathematical deficiencies of the NEPP. The advantage of the WNEPP is that the fitting curve of WNEPP more accurately coincided with the testing data was testified by further comparison. [ABSTRACT FROM AUTHOR]

A test system was designed by using a set of self-made experimental devices of coupled coal-gas in simulating mining stress effect, combining the equipment with RMT-150B rock mechanical experimental system, monitoring the rupture process of coal-rock with an acoustic emission (AE) device and collecting gas-flow rate and gas-stress data in real-time automatically with a gas flow-meter and gas pressure sensor. The fracture process and permeability properties test of the coal-rock in mining stress effect was carried out. Test results indicate that AE events and variation of stresses have the same variance tendency and the rupture process of coal-rock can be monitored by AE. The relation curves among stresses, parameters of AE and permeability properties demonstrate that the permeability of coal-rock decreases gradually at quasi-elastic stage, increases gradually at plastic damage micro-fracture stage, rises suddenly near the peak point and has multi-variation at post-peak slip stage. From the results, such conclusion can be drawn that the variation of permeability can be monitored by AE parameters or stress change. [ABSTRACT FROM AUTHOR]