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The construction of an underground coal mine reservoir plays an essential role in the ecological environment of arid areas. The moisture content and loading angle inclination significantly impact the strength and stability of the safety coal pillar of underground reservoirs. Water-bearing coal was investigated under a coupled compression–shear load using inclined uniaxial compression tests on coal samples with varying water contents (ω = 0%, 2.42%, 5.53%, 7.55%, and 10.08%) and acoustic emission (AE) technology. The weakening mechanism of the mechanical property parameters and the crack evolution law, combined with the characteristics of the stress–strain curve, the cumulative AE count, and the cumulative AE energy methods, were used. Therefore, the evolution law of the coal’s crack closure (CC) threshold, crack initiation (CI) threshold, and crack damage (CD) threshold was analyzed. The results indicate that coal samples’ peak stress and elastic modulus decreased when the water content or inclination angle increased. Peak shear stress decreased as the water content rose, and the overall characteristics gradually rose as the inclination angle increased. The exception was when the ratio was 10.08%; when the inclination angle was 0°, the failure mode of the coal sample progressively changed from tension failure (ω = 0%, 2.42%) to tension–shear composite failure (ω = 5.53%), and finally to shear failure (ω = 7.55%, 10.08%). When the inclination angle was 5°, the coal sample was dominated by tension–shear composite failure at any moisture content. When the inclination angle was 10° and 15°, the coal specimens showed shear failure at any moisture content. The evolution law of tensile and shear cracks determined by AE characteristic parameters was consistent with the macrofracture characteristics of the coal specimens. When the water content or inclination angle increased, the crack closure threshold, crack initiation threshold, and damage threshold of the coal samples decreased. Therefore, these results show that their peak stress ratio does not depend on the water content or inclination angle.

The mechanical behaviors of commercially pure titanium (CP-Ti) sheets under uniaxial and reverse loadings along various in-plane directions are investigated by crystal plasticity modeling together with experiments. The elastic viscoplastic self-consistent (EVPSC) crystal plasticity model, that incorporates an enhanced twinning and detwinning (TDT) scheme to consider multiple twinning modes, is employed for the crystal plasticity modeling. The in-plane anisotropic, the tension-compression asymmetric, and the unique work hardening behaviors of the CP-Ti sheets are ascribed to available deformation mechanisms. In addition to various deformation slips (e.g., prismatic, basal and pyramidal c + a slips), deformation twinning and detwinning of extension ( { 10 1 ¯ 2 } ) and contraction ( { 11 2 ¯ 2 } ) twinning modes are deliberated in particular. The effect of the mechanisms on the evolution of the stress strain relation, hardening rate, texture, relativity activities, and twin volume fractions, etc. is explored. It is found that twinning and detwinning of both extension and contraction twins, as well as deformation slips, affect significantly the behaviors of the CP-Ti sheets. The modeling results agree well with the corresponding experiments. The difference of the mechanical behaviors between the two sheets and the difference among various loading conditions are ascribed to the different combination of the operative deformation mechanisms, especially the contribution from twinning and detwinning of extension and contraction twins.

The increasing anthropogenic CO2 emission and global warming has challenged the China and other countries to seek new and better ways to meet the world’s increasing need for energy while reducing greenhouse gas emissions. The overall proposition of this research is to develop a brand-new CO2 physical and chemical sequestration method by using solid waste of coal mining and cementitious material which are widely used for goaf backfilling in coal mining. This research developed a new testing system (constant temperature pressurized reaction chamber (CTPRC)) to study the effects of different initial parameters on mineral carbonation such as different initial water-binder ratio, initial sample porosity and initial carbon dioxide pressure. The experimental results show that the CO2 consumption ratio is 15%, 10% and 7% higher with relatively high initial water-binder ratio, initial sample porosity and initial CO2 pressure within 48 h. In addition, some physical and chemical evidence was found through the electron microscope scanning and XRD test to further explain the above test results. This proposed research will provide critical parameters for optimizing CO2 sequestration capacity in this cementitious backfilling material with forming agent.

The pore structure of coal reservoirs determines the reserves of coalbed methane, and the gas permeability determines the level of the production capacity. In this study, the SEM images of coal samples were analyzed by various means. First, the grayscale threshold of binarization of the coal sample image is determined by a suitable algorithm. Comparing several different algorithms, the porosity based on Yen algorithm is closer to the results of vacuum saturation method and nuclear magnetic resonance (NMR) (8.35% vs. 7.51% vs. 8.92%). Further, the pore size distribution (PSD) of the coal sample is obtained according to discrete and continuous algorithms. By comparing the SEM results with the NMR results, it is found that the calculation results based on the continuous algorithm (CPSD) are better than the discrete algorithm (DPSD) and closer to the NMR results. For the effect of scale, we found that the image resolution has a certain influence on the minimum pore size characterized, such as sample C1: 0.29 μm ( × 1000) vs 0.58um ( × 500). At high resolution, more micro-pores are observed. Further, we predict the permeability of coal samples based on SEM images. It is found that the calculation results based on the continuous algorithm and the Hagen–Poiseuille equation are closer to the measured values (e.g., 16.97 (DPSD) vs. 0.45(CPSD) vs. 0.59 mD (Lab), sample C2, magnification of × 1000). In general, this method can effectively evaluate the pore structure characteristics and permeability of coal samples.

Permeability is one of the important parameters to evaluate the long-term sealing performance of Callovo-Oxfordian (COx) argillite for high-level radioactive waste repository. In this stud...

Strain rate is not only an important influence factor for deformation property but also an important parameter for analyzing the dynamic mechanical behavior of rock material. In this study, the dynamic compressive mechanical properties of saturated yellow sandstone at four strain rates and six freeze-thaw temperatures are investigated by using the SHPB test system. The coupling effect of strain rate and freeze-thaw temperatures on the mechanical parameters of rock material are discussed in detail, and the relationship formula of peak strain and dissipated energy with strain rate and freeze-thaw temperature are also established. Finally, the fractal dimension characteristic of fracture specimens with the strain rate and temperature are analyzed by using the fractal dimension method. The research results indicate that (1) with the increase of strain rate, the increase speed of peak strain, peak strength, and dissipated energy at medium strain rate level was obviously higher than that at high strain rate level, indicating that the strain rate effect weakened at high strain rate. (2) Freeze-thaw temperature can improve the brittleness-ductile transformation rate of saturated specimens. (3) According to the strain rate sensitivity coefficient, at room temperature, the strain rate effects on peak strain and peak strength are weakest, while at -20°C ~ -30°C, they are most significant. In addition, the strain rate effect on dissipated energy is significant at room temperature, while weakest at -30°C. (4) The fractal dimension gradually increases with strain rate increasing or freeze-thaw temperature decreasing, indicating that the freeze-thaw environment has a positive function for increasing the damage and fracture degree of specimens for saturated specimen. Our research results can provide an extremely important theoretical basis for the dynamic disaster prevention and structural design of rock engineering in cold regions.

Solid backfill coal mining (SBCM) is a green mining technology which can effectively alleviate the environmental problems induced by traditional coal mining techniques, such as surface subsidence, water resources loss, coal gangue occupation, and pollution. In this study, a multilayer Winkler foundation beam model for the overburden key strata is proposed, and the model with two key strata is solved. The subsidence, rotating angle, inner force, and stress of the overburden key strata are systematically analyzed under various backfill elastic modulus, mining height, and soft layer thickness. The results show that the subsidence of the key strata exhibit “basin”-shape curves, and the backfill elastic modulus, mining height, and the thickness of the soft strata have significant influences on the subsidence of the key strata. The shear stress, horizontal stress, and vertical stress of key stratum can be effectively reduced by increasing the backfill elastic modulus. The increase of mining height has little influence on the stress of key stratum that close to the coal seam (key stratum #1), but has a significant effect on the stress of key stratum that above the soft layers (key stratum #2). On the contrary, the effect of increasing soft layer thickness on the stress of key stratum is opposite to that of increasing mining height. In addition, the shear failure of key stratum #1 at mining boundary and the tensile failures on both sides of mining boundary should be preferentially considered in SBCM engineering design. Due to the low shear stress level of key stratum #2, the tensile failure on both sides of the mining boundary should be mainly considered.

In this paper, the dynamic loading tests of sandstone after heat treatment at 25-800?C are carried out by using the split Hopkinson pressure bar test system. Combined with the theory of energy dissipation, the dynamic fracture and energy consumption characteristics of coal-series sandstone are systematically studied. The test results illustrate that the dynamic fracture and energy consumption characteristics of sandstone are mainly related to the changes of internal moisture and cementing materials.

Two mean-field crystal plasticity models of the Taylor model and the Affine model have been employed to study the large strain behaviors of OFHC copper under uniaxial compression, uniaxial tension, plane strain compression, simple shear and fixed-end thin-walled tubular torsion. The effect of latent-hardening on the predictability of the models is assessed through comparing the simulated results with the corresponding experiments. Both the stress strain curves at macroscale and the deformed textures associated with microscopic deformation mechanisms are investigated. From the assessment, Affine model with isotropic latent hardening effect gives the overall best performance among all the models and latent hardening factors examined.

This study presents the particle size distribution of aggregate effects on the mechanical and structural properties of cemented rockfill. The uniaxial compression tests with acoustic emission (AE) monitoring, ultrasonic tests and scanning electron microscope (SEM) tests were carried out on the cemented rockfill, for which the aggregate particles satisfied the Talbot gradation theory. The particle flow model was constructed in the numerical software of PFC3D to reproduce the crack evolution and particle failure of cemented rockfill specimen. The AE characteristics, microstructures, numbers and distributions of initiated cracks and particle failure models of cemented rockfill under different particle size distributions of aggregates were discussed. The influence mechanism of the particle size distribution of aggregate on the strength, dilatancy and ultrasonic properties of cemented rockfill was analyzed. The results showed that the cemented rockfill with the overly fine or coarse particle size distribution of aggregate not only presented the more deteriorative microstructures, but also had the more early damaged areas with active AE signals and more initiated cracks during loading. However, the strength of cemented rockfill related to the crack distribution in the structure in addition to the number of initiated cracks. The concentration of cracks in the structure also caused the particle failure mode to present a certain dilatancy to further affect the loading capacity of the cemented rockfill. Among all the specimens, the cemented rockfill with Talbot index of 0.6 performed the relatively dense microstructures, superior structural properties and symmetric and uniform distribution of initiated cracks leading to optimize its strength, deformation and ultrasonic properties.

Geomaterials generally show strain-softening characteristics after peak-load. Based on the triaxial test for sandy mudstone, a simple elastopeak plastic-strain-softening-damage model (EPSDM) was proposed. Compared with the traditional strain-softening model, EPSDM shows obvious plastic bearing characteristics before strain softening. Then, the closed-formed solution of circular opening was deduced based on the newly proposed model. A plastic shear strain increment was introduced as the extension constraint condition of peak plastic zone. The solution correctness of EPSDM was also verified by comparing with other research results. In addition, the solution based on EPSDM could degenerate for a series of results obtained by elastobrittle plastic model (EBM), elasto-strain-softening model (ESM), and elasto-perfectly plastic model (EPM) under certain conditions. Hence, it could be regarded as a unified solution. Finally, the research results denoted that when the inner pressure was fully released, the maximum postpeak failure radii and surface displacement of surrounding rock indicated the characteristics of EBM>ESM>EPSDM>EPM. Therefore, the plastic bearing behavior could effectively decrease the postpeak failure zone radii and surface displacement. The dilation coefficient noticeably influenced postpeak failure range and surface displacement, particularly the damage zone radii and tunnel wall convergence. The research results can provide very important theoretical bases for evaluating the tunnel stability and support design reliability for underground engineering.

The gas outburst potential is typically high when roadways uncover the gassy coal seams associated with outburst hazards. This paper describes the complex stress and displacement evolution that occurs in roadway tunnelling through coal seams under different original stress conditions, which is helpful for better understanding how the stress leads to an outburst accident, and proposing some relevant control measures. The stress concentration is primarily resulted from the strength difference between coal and rock, and the abutment stress increases gradually as the forward residual rock thickness decreases when the roadway excavation enters a coal seam from rock stratum. When the abutment stress is sufficiently high, the forward residual rock will suddenly be broken after the next cycle, and the stress will decrease rapidly to release elastic energy and generate new fractures. Meanwhile, the coal and rock in front of the heading face will move rapidly towards the free space. Therefore, an outburst accident may occur immediately when the gas pressure in front of the heading face is high enough. Once the outburst accident is triggered, the gas expansion energy and elastic energy distant from the heading face will contribute to developing the accident. The stress perpendicular to the roadway is the primary factor causing such outbursts. The abutment stress concentration will be higher when the maximum original stress is perpendicular to the roadway, which will increase the outburst potential. Therefore, it is suggested that arranging roadways parallel to the maximum original stress, if possible, can also reduce the outburst threat. Outbursts are triggered by the elastic energy near the heading face and developed by the gas expansion energy and elastic energy distant from the heading face. In this study, the method of “strong-weak” coupling circle-layers was proposed to reduce the outburst hazard when roadways excavated through gassy coal seams. This method was proven to be valid by the comparative experiment. The weak circle can be realized by boreholes and hydraulic cutting. It could not only reduce the elastic energy near the heading face but also prevent the distant energy from contributing to the outburst accident. In addition, the strong circle can be made by injecting water slurry and applying anchors. It could help to reduce the strength difference between coal and rock, thereby decreasing the local stress concentration, resisting the residual outburst energy near the heading face, and preventing the outburst from being triggered. The “strong-weak” coupling structure was successfully applied in Bailongshan coal mine when uncovering the #7,8 coal seam. This structure can effectively promote gas drainage, reduce the coal and gas outburst risk. As a result, the mining efficiency improves a lot, and the uncovering time greatly decreases from the expected 2 years to 5 months.

Gas migration/breakthrough in saturated bentonite is an important issue for the evolution of the sealing ability of the engineered barrier in deep geological repositories. The main contribution of our study is to provide insights into the water and gas transport properties in a compacted bentonite/sand mixture, which was wrapped by a flexible Viton™ membrane directly before being put into a triaxial cell. The experimental results indicate that the water permeability is very low and the magnitude is in the order of 10−20 m2. Gas breakthrough tests show that no continuous gas flow was detected during the entire gas breakthrough test (until the gas pressure of 10 MPa), which indicates that the compacted bentonite/sand mixture has a good sealing ability after full saturation. Another important finding is that the gas migration properties are closely related to the stress state around the sample, the internal pore fluid pressure, and the creep effects caused by the two factors.

This study investigated the thermal expansion characteristics of coaly mudstone specimens at temperatures ranging from room temperature up to 800 °C. The experiments were performed by an MTS810 electro-hydraulic servo system and an MTS653.02 high-temperature furnace. Results revealed that mudstone experienced thermal expansion at high temperature, and that the relationship curve between thermal expansion strain and testing time could be divided into three stages. With increasing temperature, mudstone’s thermal strain and expansion coefficient exhibited an upward trend. With 400 °C as the critical temperature, the curve could be divided into (1) rapid increase stage, (2) flat stage, and (3) rapid increase stage. The major causes behind thermal expansion are changes in internal pores and fissure, as well as the thermochemistry effect of mineral components.

Comprehensive understanding of the effects of temperature and inclination angle on mechanical properties and fracture modes of rock is essential for the design of rock engineering under complex loads, such as the construction of nuclear waste repository, geothermal energy development and stability assessment of deep pillar. In this paper, a novel inclined uniaxial compression (inclined UCS) test system was introduced to carry out two series of inclined uniaxial compression tests on granite specimens under various inclination angles (0&ndash, 20&deg, ) and treated temperatures (25&ndash, 800 &deg, C) at 5&deg, inclination. Experimental results revealed that the peak compression stress and elastic modulus gradually decreased, while peak shear stress increased nonlinearly with the increasing inclination angle, the peak compression and shear stress as well as elastic modulus slightly increased from 25 to 200 &deg, C, then gradually decreased onwards with the increasing temperature. The effect of temperature on peak axial strain was the same as that on peak shear displacement. Acoustic emission (AE) results suggested that the relationship between crack initiation stress, inclination angle and treated temperature followed a similar trend as that of the peak compression stress and elastic modulus. Particularly, the crack initiation (CI) stress threshold and shear stress corresponding to CI threshold under 800 &deg, C were only 7.4% of that under 200 &deg, C and revealed a severe heat damage phenomenon, which was consistent with the results of the scanning electron microscopy (SEM) with the appearance of a large number of thermal pores observed only under 800 &deg, C. The failure modes tended to shear failure with the increasing inclination angle, indicating that the shear stress component can accelerate sliding instability of rocks. On the other hand, the failure patterns with different temperatures changed from combined splitting-shear failure (25&ndash, 400 &deg, C) to single shear failure (600 and 800 &deg, C). The study results can provide an extremely important reference for underground thermal engineering construction under complex loading environment.

In this paper, mudstone in coal measure rock strata was investigated to understand the brittle–ductile transition characteristics of mudstone under high temperature. An electrohydraulic ser...

Magnesium and its alloys are characterized by a strong basal texture, resulting in severe anisotropy at low temperature. To investigate the deformation behavior of a rolled magnesium alloy AZ31 at room temperature, uniaxial compression and tension experiments along four directions were performed and modeled using both the EVPSC-TDT and the VPSC-TDT models. The required threshold stress parameters were determined by curve fitting. Similar parameters were found to fit relatively well for all the experimental flow curves for both models. The predictions of the two models are also very similar beyond the elastic strain. The simulations reveal only a very limited increase with strain of the threshold stress for basal slip, which is favorable for basal texture development, whereas the threshold stresses for other deformation modes increase significantly. A discrepancy between experiments and simulations suggests that depending on loading condition strain accommodation between grains by basal slip varies in ease. A deformation-path dependent discrepancy between the modeled stress and the experimental curves is also found for the threshold stress for {10−12} twinning. This discrepancy is assumed to be related to the larger number of twin variants activated in tension as compared to compression, due to twin boundary hardening. A {10−12} twin-associated hardening, primarily on pyramidal slip and prismatic slip systems, evaluated to be about 15 MPa for both through thickness tension and in-plane compression, is included in the model via the use of a higher latent hardening modulus these slip systems by twinning.

The microscopic morphology and pore structure characteristics of concrete with composite admixtures (fly ash and mineral powder) after chlorine salt erosion were analyzed via scanning electron microscopy (SEM) and mercury injection porosimetry (MIP), providing the basis for the design and maintenance of concrete shafts in coal mines. The above-mentioned characteristics were compared with the macroscopic characteristic of concrete fractures under uniaxial compression. The results show that the macroscopic fracture characteristics of concrete under uniaxial compression change from longitudinal split fracture and oblique section shear fracture to conjugate cant fracture, and the degree of breakage increases. Interface cracks, cement paste cracks, spherical surface cracks, and aggregate cracks appear in concrete under uniaxial compression. In the early stages of corrosion, the original cracks which are obvious are repaired. When the corrosion becomes more serious, cement paste cracks appear, and the number of harmful holes increases while the number of harmless holes decreases. This study also reveals the relationship between the macroscopic properties and microscopic structure of concrete under chloride salt erosion. Finally, the paper preliminarily discussed the relationship between the macroscopic properties and mesoscopic characteristics of concrete under chlorine salt erosion. Keywords: Concrete, Chlorine salt erosion, Mesoscopic characteristic, Damage fracture

In plane tension of magnesium alloy sheets is accommodated by prismatic and basal slip, whereas {10−12} twinning is activated when grains are elongated along the axis. The plastic behavior of Mg-3Al-1Zn in tension has been investigated using a thick rolled plate with a strong basal texture. Tensile tests were performed along five directions distributed between the normal direction and the transverse direction, allowing various amount of {10–12} twinning, basal, and prismatic slip to take place. The twinning behavior has been investigated using EBSD measurement and EVPSC modeling, and Schmid factor analysis was performed. The observed amount of variants with a Schmid factor of high rank is higher than predicted, emphasizing the necessity of strain accommodation between grains and twins. Compared with compression, even when twinning activity is low, more {10–12} twin variants are predicted in tension. This study confirms extension twinning as a major deformation mechanism in all tensile directions and an efficient way to harden Mg alloys by twin-twin boundaries. Keywords: Magnesium alloy, AZ31, Twinning, Crystal plasticity, EVPSC

The characters of limestone in weak interlayer of a high rocky slope in Xuzhou, China, are studied by shear static test and shear creep test. The results show that limestone specimens have attenuation creep properties and constant rate creep properties, almost have no accelerated creep properties. The exponential type empirical formula is selected to fit creep grading curves by polynomial regression analysis method, and the square sums of the fitting results residual are in the order of 10−7. Then grade creep curves at every shear loads are set up. Combining creep rate-time curve, the creep properties of limestone are analyzed. As the physical meaning of component model is clearer, the Poytin–Thomson model is set up. Through the least square method, the optimal parameters of Poytin–Thomson model are obtained, and the sums of squared residuals belong to 10−3 order of magnitude, which can meet the accuracy requirements of engineering calculation. So the Poytin–Thomson model can reflect the shear creep characteristics of limestone very well. Keywords: Limestone, Shear creep property, Empirical formula, Poytin–Thomson model

A model accommodating multi-scale pores containing kerogen within an inorganic matrix is used to explore the complex multi-mechanistic transport mechanisms of shale gas reservoirs. These include the complex evolution of pressure, diffusion and flow within both kerogen and inorganic components and their interaction with effective stresses. A general poromechanical model is proposed considering desorption and molecular diffusion in the kerogen, viscous flow in the inorganic matrix and fracture system, and composite deformation of the triple porosity assemblage. The model is verified by history matching against field data for gas production rate. The simulation results indicate that the pattern of gas flow is sequential during gas depletion – pressure first declines in the fracture, followed by the inorganic phase and then in the kerogen. The evolution of permeability is pressure dependent and the evolution of pressure is closely related to the intrinsic gas diffusion coefficient in the kerogen, inorganic matrix intrinsic permeability and fracture intrinsic permeability. A series of sensitivity analyses are completed to define key parameters affecting gas production. The study shows that dominant influence of the fracture network in acting as the main permeable conduit. The intrinsic permeability and porosity of the fracture have a positive correlation with gas production, while fracture spacing has a negative correlation to gas production. Kerogen also plays a critical role in gas production for shale reservoirs with higher total organic carbon. The enhancement of inorganic matrix permeability and gas diffusion coefficient in kerogen could efficiently guarantee a long-term gas production with a higher rate.

Many projects such as the underground gasification of coal seams and coal-bed methane mining (exploitation) widely involve the dynamic problems of coal measures sandstone achieved via thermal treatment. This study examines the dynamic mechanical properties of coal measures sandstone after thermal treatment by means of an MTS653 high-temperature furnace and Split Hopkinson pressure bar test system. Experimental results indicate that 500 °C is a transition point for the dynamic mechanical parameters of coal measures sandstone. The dynamic elastic modulus and peak strength increase linearly from 25 to 500 °C while the dynamic peak strain decreases linearly over the same temperature range. The dynamic elastic modulus and peak strength drop quickly from 500 to 800 °C, with a significant increase in the dynamic peak strain over the same temperature range. The rock mechanics are closely linked to material composition and mesoscopic structure. Analysis by X-ray diffraction and scanning electron microscopy indicate that the molecules inside the sandstone increase in density due to the thermal expansion of the material particles, which effectively improves the deformation resistance and carrying capacity of the sandstone and reduces the likelihood of axial deformation. With heat treatment that exceeds 500 °C, the dynamic mechanical properties rapidly weaken due to the decomposition of kaolinite; additionally, hot cracking of the mineral particles within the materials arises from coal sandstone internal porosity, and other defects gradually appear.

Effects of hoisting parameters (effective load, acceleration and deceleration) on dynamic contact characteristics between the rope and friction lining in a deep coal mine were analyzed in this study. Effects of hoisting parameters on dynamic tensions during hoisting with variable acceleration and deceleration were explored employing Simulink simulations. Roles of hoisting parameters on contact states, slip amplitude and stress distributions along the contact path were investigated using finite element analyses. The results show distinct tensions and tension differences at both rope ends with different hoisting parameters. Dynamic contact states consist of sticking, slip and mixed regimes during hoisting. Increases of hoisting parameters induce overall increased possibilities of the gross slip, increased stress concentrations and accelerated wear between contacting bodies.

A detailed understanding of damage evolution in rock after high-temperature treatment in unloading conditions is extremely important in underground engineering applications, such as the disposal of highly radioactive nuclear waste, underground coal gasification, and post-disaster reconstruction. We have studied the effects of temperature (200, 400, 600 and 800 °C) and confining pressure (20, 30 and 40 MPa) on the mechanical properties of sandstone. Scanning electron microscopy studies revealed that at temperatures exceeding 400 °C, new cracks formed, and original cracks extended substantially. When the confining pressure was 20 MPa, a temperature increase from 400 to 800 °C resulted in a 75.2% increase in peak strain, a decrease in Young’s modulus and peak strength of 62.5 and 35.8 %, respectively, and transition of the failure mechanism from brittleness to ductility. In the triaxial compression tests, the specimen deformed in a more obvious ductile failure manner at higher confining pressure, whereas in the unloading confining pressure experiments, brittle failure was more obvious when the initial confining pressure was higher. We focused on the effects of temperature and initial confining pressure on peak effective loading stress and peak ductile deformation during unloading. At temperatures of >400 °C, the peak ductile deformation increased rapidly with increases in the high temperature treatment or initial confining pressure. The peak effective loading stress decreased sharply with increased temperature but barely changed when the initial confining pressure was varied.

In this study, the patterns of chloride ion erosion of unsaturated concrete subjected to the coupling action of cyclic loading and salt spray corrosion were experimentally studied, and Fick&rsquo, s Second Law was used to fit the variation patterns of chloride concentration to obtain the chloride diffusion coefficient. Accordingly, we have established a mathematical model that describes chloride transport in unsaturated concrete and accounts for the effects of gas flow, water migration, convection diffusion, and capillary action. This model is composed of three equations&mdash, the gas flow equation, the solution flow equation, and the solute convection&ndash, diffusion equation. The COMSOL numerical analysis software was subsequently used to obtain solutions for this model, based on parameters such as porosity and the chloride diffusion coefficient. Subsequently, the saturation, relative permeability, and the chloride ion concentration during the first corrosion cycle were analyzed. The numerical results were consistent with the experimental values and were therefore superior to the values obtained using Fick&rsquo, s Second Law.

In this study, water retention tests under free swelling conditions were performed to investigate the water intake (or loss) behaviour of compacted GMZ bentonite. First, the water retention characteristics were investigated, and then the microscopic pore structure was observed by environmental scanning electron microscope (ESEM). The results indicate that GMZ bentonite has a strong swelling (or a limited shrinkage ability) due to water intake (loss). The suction behaviour of GMZ bentonite is similar to MX80 bentonite and FEBEX bentonite. We also find that the confinement conditions can affect the suction behaviour of the material, especially at high relative humidity (RH). Additionally, a mathematic model can fit the mass change data very well. Microscopic tests show that the granular sensation of GMZ bentonite is obvious for a sample at low RH. With the increase in RH, the surface of GMZ bentonite becomes more smooth. The differences in the porosities calculated by the macroscopic and microscopic tests can be attributed to image resolution. The inter-laminar pores and intra-aggregate pores cannot be observed by the ESEM method. In addition, ESEM observation can provide an intuitive basis for the further research of the seepage property of GMZ bentonite.

It is of great significance, for economic, environmental and security reasons, to investigate the strength characteristic of underground cemented paste backfill (CPB). Consequently, an ultrasonic test, uniaxial and triaxial compression experiment, and acoustic emission (AE) monitoring were carried out on CPB, for which the particles satisfied Talbot gradation. The homogeneity of CPB specimens was evaluated by ultrasonic pulse velocity (UPV). The stress&ndash, strain behavior and AE characteristic of CPB specimens under different Talbot indices and confining pressures were investigated. The effects of the particle size distribution and the confining pressure on the peak strength of CPB were analyzed. The strength parameter model of CPB under the coupled influence of the particle size distribution and the confining pressure was constructed based on the Mohr&ndash, Coulomb strength criterion. The results show that the peak strength of CPB is positively linear with confining pressure, however, the relationship between its strength parameters and the Talbot index can be characterized by a quadratic polynomial function. This suggests that there is an optimal gradation of particles reflected in the maximum strength of CPB.