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Temperature is a major factor affecting physical and mechanical rock properties. With increasing temperature, a series of variations enlarge the internal defects within rocks, resulting in physical and mechanical rock property variations. To explore the influence of temperature on the physical and micro-structure of limestone, the weighing test and P-wave velocity test were conducted on limestone after exposure to high temperature to reveal the evolution of the limestone mass and P -wave velocity. XRD, XRF, SEM, and mercury intrusion tests were also carried out to examine the mineral composition and content, micro-fracture morphology, porosity, and fractal dimension. The limestone mass and P-wave velocity decrease with increasing temperature. When T ≤ 400 °C, there is no obvious change in chemical composition and crystal structure; when T = 400–500 °C, the diffraction intensity of partial calcite decreases, and dolomite decomposes gradually; when T > 500 °C, illite decomposes gradually, while dolomite decomposes completely; and the diffraction intensity of calcite is significantly reduced. When T ≤ 200 °C, changes in trace minerals or impurities containing K2O and Na2O and the decomposition of illite oxide are dominant; when T = 400–600 °C, illite oxide, trace minerals, or impurities containing K2O and calcium hydroxide begin to decompose. When T = 600–800 °C, magnesite and dolomite begin to decompose. When T ≤ 200 °C, micro-fracture surfaces change slightly. When T = 200–500 °C, micro-fractures begin to develop and propagate gradually, most of which are intergranular cracks with a small number of transgranular cracks. When T > 500 °C, transgranular cracks occur in samples with locally broken crystals, and the cracking of the crystal structure occurs with increasing pore size. With increasing temperature, the limestone pore fractal dimension decreases gradually, and the higher the temperature, the greater the decrease. 400 °C to 500 °C is the temperature threshold interval that causes the pore structure change. These new pores, resulting from the increasing temperature, are primarily mesopores with a pore diameter of 1.0–10.0 μm. This research provides a scientific basis for the design and construction of rock engineering projects to be subjected to high temperatures, deep geological radioactive nuclear waste disposal sites, deep mines, and the exploitation of geothermal resources.

This study derived the analytical solutions for the deflection, bending moment and shear force of a hard roof under an arbitrary front abutment pressure for both the initial and periodic fracture problems using the elastic foundation beam model. With the assumption that the overburden pressure is constant in a small section, the roof subjected to arbitrarily distributed pressures is divided into a number of sufficiently small sections, whose closed-form solutions can be obtained easily. The proposed analytical solutions are validated by comparisons with those calculated using a model reported in the literature, in which the overburden pressure is assumed to follow a normal distribution. The parametric studies on the foundation stiffness, front abutment pressure and support resistance show that: (1) with the decrease of elastic foundation stiffness, the deflection and the maximum bending moment significantly increase, and the shear force significantly changes in the unmined region; (2) as the peak point position moves inside the coal wall, the deflection of the goaf roof, as well as the maximum bending moment and shear force, obviously decrease; (3) with the increase of support resistance, the maximum bending moment and deflection significantly decrease, and the shear force significant decreases in the hydraulic support region; (4) when the coal seam is soft and peak position of the front abutment pressure is near the coal wall, initial fracture occurs at the midspan; otherwise, it occurs inside the coal wall. For the periodic fracture condition, the fracture position is closer to the coal wall when the coal seam is harder, and the fracture length increases when the peak position of front abutment pressure moves inside the coal wall.

During the failure process, granite always exhibits strain-softening behavior and confining pressure-dependent effect. Based on triaxial cyclic loading and unloading compression tests, the evolutions of cohesive strength, internal friction angle, and elastic modulus with axial plastic strain and confining pressure were obtained. The results show that both the cohesive strength and the internal friction angle first increase and then decrease with an increase in the axial plastic strain. Meanwhile, the elastic modulus increases with an increase in the confining pressure and decreases with an increase in the axial plastic strain. Considering the evolutions of the cohesive strength, the internal friction angle and the elastic modulus, an improved strain-softening constitutive model was proposed. The proposed model was further embedded in the Fast Lagrangian Analysis of Continua (FLAC) procedure, based on which the conventional triaxial cyclic loading and unloading tests were simulated. The simulated results have shown a good agreement to the experimental results.

Understanding the mechanical behavior of rock under conditions of high temperature and pressure is critical when it comes to implementing underground coal gasification, deep disposal of highly radioactive nuclear waste, development and utilization of deep underground space, development and utilization of geothermal resources, etc. To understand the effect of confining pressure on limestone at high temperature, uniaxial and triaxial compression testing was conducted on limestone under high temperature (20–800 °C) using the MTS 815 rock mechanics testing system. Using this system, the change in the strength and deformation parameters of the limestone at varying temperature and confining pressure conditions were studied. The results show that the triaxial compression stress-strain curve of limestone at high temperatures is divided into five stages: compaction stage, elastic stage, plastic deformation stage, post-peak failure stage, and residual stage. In addition, the rock brittleness and ductility decrease as the temperature increases. The peak stress and residual strength of the limestone at high temperatures increase as the confining pressure increases, and the strength of the rock specimens decreases as the temperature increases. The internal friction angle (φ) first increases and then decreases as the temperature increases, but the relationship of the cohesive force (c) to temperature is opposite that of φ, indicating that the shear strength of limestone at high temperatures is determined by both c and φ. The elastic modulus of limestone at high temperatures increases with the increase in confining pressure and decreases as the temperature increases, and the peak strain of limestone at high temperatures increases as the confining pressure and temperature increase. The effect of temperature on the failure of limestone is not obvious, and the failure of rock specimens during uniaxial compression testing was mostly through axial splitting, while the failure of rock specimens under triaxial compression testing was mostly through shear failure. As the confining pressure increases, the fracture type of the rock specimens gradually changes from brittle tensile fracture to shear fracture, and the instability type of the rock specimen changed from the sudden instability type to the progressive failure type. Our research results are especially useful in areas where engineering is performed on rocks under high temperature.

A piecewise-linear large-strain radial consolidation model, called VRCS1, is developed for soft soil stabilized by prefabricated vertical drain (PVD) assisted by vacuum-surcharge combined preloading incorporating non-Darcian flow and nonlinear compressibility and permeability relationships. VRCS1 accounts for large strain, soil self-weight, smear effect, partial drain penetration, time-dependent surcharge loading, time- and depth-dependent vacuum pressure, unload/reload effects, radial and vertical flows, hydraulic conductivity anisotropy, non-Darcian flow and nonlinearly varying relationships of compressibility and permeability. The compressibility and permeability constitutive relationships are specified using discrete data points and, as a result, VRCS1 is more flexible than other existing models in terms of considering a variety of different constitutive relationships. VRCS1 shows excellent agreement with other exiting solutions and field measurements involving Darcian flow and non-Darcian flow, surcharge loading and surcharge-vacuum combined loading, and small and large strains. A series of numeric examples indicates that compressibility and permeability relationships can have significant effect on the rate of radial consolidation. Results also indicate that solutions based on small-strain theory can be in significant error for large strain conditions, especially when non-Darcian flow and nonlinear constitutive relationships are encountered.

This paper presents a large strain numerical solution of a circular tunnel for the ground reaction curve (GRC) in strain-softening rock masses. Both the stress equilibrium equation and deformation compatibility equation are considered in a current coordinate. A series of examples are employed to validate the proposed solutions, and the results show that: (1) the displacement, softening and residual radii of larger strain solution are smaller than that of small strain solution, and their difference significantly increases with a decrease in the Young’s modulus. (2) the increasing Poisson’s ration and critical shear plastic strain decrease the displacement, softening and residual radii.