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To reveal the damage characteristics and catastrophic failure mechanism of coal rock caused by gas adsorption, physical tests and theoretical methods are employed. The results show that adsorption swelling can damage coal rock, which can be distinguished by fractal dimension. A fitting relationship between the adsorption damage and fractal dimension is proposed by experimental testing and theoretical analysis. High gas adsorption pressure proves to be the dominant factor that leads to coal failure softening and gas outburst disasters. Three main parameters concerning adsorption damage include the change rate of released energy density, the transition difference in the post-peak acoustic emission (AE) b value and the change rate of cumulative AE energy. Results show that all the three parameters present a step-type decreasing change with the increase in fractal dimension, and the fractal dimension shows a linear relationship within the same failure mode. Finally, a method is proposed to evaluate coal rock disaster transformation, based on the aforementioned three main parameters of adsorption damage.

Compression-induced shear-mode cracks play an important role in the failure process of rocks. To gain insight into the compression-induced shear-mode cracks in rocks, the initiation and propagation of compression-induced shear-mode cracks are investigated via physical experiments and numerical simulations. The experimental results show that compression-induced shear-mode cracks are a common fracture mode and often lead to final failure. The initiation and propagation of compression-induced shear-mode cracks, as well as the strength of the specimen, can be influenced by the spacing between the flaw tips. Compression-induced shear-mode cracks easily initiate and propagate when the spacing between the two pre-existing flaws is small, whereas a larger spacing can reduce the possibility of shear fracturing and is propitious to the generation of compression-induced tensile-mode cracks. In addition, compression-induced shear-mode cracks initiate and generate later than compression-induced tensile-mode cracks. Furthermore, the fracture angles of compression-induced shear-mode cracks are diverse and complex and can be influenced by the spacing between pre-existing flaws. Numerical simulation results suggest that compressive-shear failure initiates randomly in a shear stress field, becomes more localized with the increased loading and eventually results in compression-induced shear-mode cracks.

To study the characteristics and mechanism of slip failure in coal rock mass containing weak interlayers in deep underground, UDEC was used to investigate coal rock mass. The results show that the weak interlayer can change the path of stress transfer, and with the increase of thickness of the weak interlayer, the horizontal displacement and stress all show an increasing trend, and the closer the monitoring point is to the wall of roadway, the greater the horizontal displacement. The depth of plastic zone also increases with the growth of the thickness of weak interlayer. Additionally, the lateral pressure coefficient has a similar influence on the horizontal displacement and stress with the thickness of weak thickness. The horizontal and vertical stresses of the coal rock mass with no weak interlayers are often the largest before the peak stress and the smallest after the peak stress. These results can help to understand the formation mechanism of slip failure in coal rock mass in deep underground and is of great significance for evaluating the safety and taking reasonable supporting measures.

The paper investigates the initiation mechanism of debris flow through the survey with detailed analysis for several field debris flow events. The field investigation shows that the debris flow evolution includes distinct three stages: the soil structure changes and forms slide debris, slide debris mobilizes into debris flow, and the debris flow slips a long distance along the slope. In order to reappear and explain the aforementioned phenomenon existing in the initiation procedure of debris flow, the vane shear rheometer device is developed to test the shear rheology properties of debris source. Subsequently, the shear rheological tests with water drained out are performed utilizing the fine sand as tested material. A series of tests are performed and experimental data are obtained including the shear strain, negative pressure, water content, shear velocity, shear resistance, pore water pressure, and line displacements on the shear surface. Based on the changes of water content and negative pressure, the unsaturated permeability coefficients are obtained to explain the water-free infiltration process in the tests. According to the changes of shear velocity and experimental phenomena, the debris flow evolution is divided into three stages including the antecedent rainfall stage, accelerated initiation stage, and long-distance movement stage, which is similar to the three corresponding stages existing in the filed debris flow events. According to the analysis of test results, the mechanics of the debris flow initiation could be explained as the following: the debris source’s shear strength decreased to the value of yield shear strength, the peak shear strength available during undrained loading of a saturated, contractive, sandy soil, after a long period of antecedent rainfall infiltration. The tiny cracks expended to form connecting crack surfaces in the debris source interior, and then the debris source moves rapidly under the continuous rainfall, indicating the debris flow initiation. During the long-distance movement stage, the particles of debris source on the shear surface rearrange and form a smooth slide surface as the values of water content and pore water pressure increase. Therefore, the increase of water content and the decrease of negative pressure caused the soil shear strength decaying, and that is the major reasons of debris flow initiation. In addition, the other key reason is the particles rearranging on the initiation surfaces. The vane shear rheometer apparatus and corresponding test results have provided a more concrete and rational mechanism interpretation for debris flow initiation.

Coal seam water injection has a significant effect on the prevention and control of coal mine rock burst, and the pore characteristics of the coal seam is an important factor affecting the effect o...

Rock burst is a catastrophic dynamic disaster caused by sudden failure and instability of coal, loading paths play an important role in the failure of coal, the coal failure process is associated with charge exception information. Hence, violent coal failure mechanics and time–frequency domain distribution of charge signal such as rock burst under different loading paths should be studied in-depth. In this paper, grade and cyclic loading test were carried out for coal with impact tendency samples produced by blocks cored from 800 depth in Xiaoqing coal mine of the Tiefa coal group in northeast China. Theory discussion was carried out for the result of stress and strain, frequency-spectra analysis was conducted for the wavelet charge data, figures showing the evolution mechanism of mechanical properties and the relationship of time–frequency domain amplitude of charge signals in coal with different loading paths and stage were obtained. The failure process and characteristics of coal under different loading paths were summarized. It found that the loading path changed the manner of energy accelerate–release, there were more plastic strain generation in coal under cyclic loading than that under grade loading, the former was more likely to cause greater damage and failure, then the strength of coal under cyclic loading is generally lower than that under grade loading, an energy conversion mechanical model of stress, damage and deformation was developed and explained the effect of the loading path. Charge signal was primarily distributed in the strengthening and peak stages, where there was a high amplitude pulse at each stress drop. The charge pulse was a type of low frequency signal with a primary frequency distribution range of 1 –100 Hz. Discussion on the charge generating mechanism from the perspective of friction slip, it demonstrated that the charge obtained during the coal failure process directly to stress loaded on and damage, the result verified it better. We propose that the research results in this study could be efficiently applied to daily mining activities, to provide an early warning and effectively avoid rock burst disaster.

The present paper focuses on the mechanical properties, permeability and energy variation within gas contained bump-prone coal, and, based on theoretical and experimental methods, the paper seeks to elucidate the complex mechanical mechanism of gas emissions with gradually varying states of stress and its catastrophic mechanisms. A triaxial test apparatus is developed specifically for stressed coal, taking the properties of gas adsorption and migration into consideration under stress conditions and providing simultaneous measurement of deformation and gas flux. The entire deformation process of coal samples with a danger of bump, obtained from a depth of 580 m in the Xinzhouyao colliery of northern China, was investigated by conventional triaxial compression experiments using various levels of confining pressure and gas. Sieve analysis was used to measure the post-failure coal fragments, and an empirical formula was developed to describe the new surface during coal failure. It was found that the existence of gas reduces cohesion and increases the internal friction angle, the strength decreases with increasing gas pressure, and the elastic modulus is gradually reduced by the influence of confining pressure. The angle of coal damage increases from the failure model of conjugate shear to single shear and tension shear with larger fractal dimensions. Permeabilities showed clear phase characteristics with coal deformation, and the theoretical analysis revealed that the gas energy is mainly derived from free gas in the fissures. With higher gas pressures and porosities of coal, larger amounts of energy were contained in the coal seams. As a consequence, the energy composition has a direct impact on disaster types, initiation and occurrence. A surplus energy evolution model and disaster tendency evaluation index for coal failure was developed and used to determine the instability type. These test results may help us gain insight into the mechanical coupling mechanism between coal and gas, even in deep mining where high in situ stresses and gas pressures may cause bump-outburst compound disasters.

The slippage initiation and induced instability of roadway surrounding rock are highly likely to cause dynamic disasters, severely influencing the safety production of mining. With the optical-mechanical monitoring test of the deformation localization of energy dissipation, this study established the optical index of coal deformation equilibrium degree under load, and obtained the evolution law of coal deformation equilibrium degree. After analyzing the relationship between tensile-sliding effect and mechanical behavior of coal deformation field, it proposed the strain energy ratio coefficient. The results indicate that the strength reduction of coal body is affected by the deformation accumulation of loading displacement field. The sliding displacement of the stable sliding type specimen occurs 5.5s earlier than tensile displacement，which is 4.4s longer than the instantaneous instability type specimen. The instability type of coal is closely related to the tangent angle of the strain energy ratio coefficient and the damage persistence characteristics. The damage accumulation of stable equal amplitude contributes to the stable failure, and the damage accumulation of interval equal amplitude influences the instantaneous instability development. The fracture expansion stage is the main stage of energy consumption damage accumulation. That is, the main energy consumption damage accumulation stage of the stable slip coal is the stable crack expansion stage, with the damage proportion of 35.89%, while the damage proportion of instantaneous instability coal in the unsteady crack expansion stage is 84.226%. The study provides theoretical reference for the fracture law and risk monitoring of coal slippage.

By means of experimental research and theoretical analysis, the nonuniform evolution characteristics of rock friction and sliding were studied. Using digital speckle correlation (DIC) as observation method, the whole process of friction and sliding of a granite specimen in double-sided shear experiment is studied. A spring slider model considering the microscopic characteristics of interface asperities was established to simulate the microscopic process of rock friction and sliding. By comparing the theoretical analysis results with the experimental results, the effect of interface nonuniformity on rock friction sliding instability is studied. The results demonstrated that, with the increase of nonuniformity of sliding interface, the degree of local instability before stick-slip decreases, the stick-slip period shortens, and the value of shear drop during stick-slip period decreases. The nonuniformity of sliding interface will increase after local instability.

Acoustic emission (AE) can be applied to identify crack propagation and damage of materials and structures. However, few studies investigate the multifractal regularity and compressive strength prediction for concrete using AE parameters. Therefore, the major objective of this research is to perform multifractal analysis of damage and develop support vector machine (SVM) for strength prediction based on AE parameters. Meanwhile, fuzzy c-means (FCM) was implemented to identify damage mechanisms. The results showed that the level of damage can be revealed qualitatively and quantitatively by analyzing morphology and parameters of multifractal. In particular, the multifractal parameter α0 has the ability to identify critical damage and primary failure surface. Moreover, damage mechanisms were further distinguished by FCM. Finally, the results showed that the parameters of AE can further expand the application of AE for predicting compressive of concrete. SVM prediction results using AE parameters perform higher precision than the artificial neural network (ANN). Furthermore, a significant reduction in sample size uses AE parameters to predict concrete strength.

Upstream tailing dams, which are commonplace, can easily lead to major accidents under seismic excitation. However, the dynamic response characteristics and causes of instability failure of tailings dams are yet to be investigated fully. In the present study, shaking-table tests were conducted to determine the acceleration, pore pressure, soil pressure, and displacement of a dam body under a seismic wave with different values of the PGA peak ground acceleration. The peak acceleration of the dam exhibited the typical spatial effect. Because of the increased shear strain of the tailings in the dam, reduced stiffness, and increased damping, the acceleration amplification factor increased with increasing elevation and decreased with increasing PGA (peak ground acceleration. The free face of the dam underwent liquefaction more easily, and the pore pressure of the dam exhibited three phases over time, namely rapid increase, sharp decrease, and then slow dissipation. The soil pressure also exhibited three phases over time, namely slow increase, rapid increase, and peak fluctuation. Once the pore pressure had dissipated, the soil pressure exhibited an inflection point at Arias intensity release. The vertical displacement of the dam increased gradually, but it is less than horizontal displacement. The pore pressure, soil pressure, and displacement were closely related to the Arias intensity. The present results have practical importance for understanding the instability of dams and reinforcement under seismic effects.

Integrin αvβ3 was reported as positive regulators of tumorigenesis and highly expressed in cancer stem cells and kinds of cancers, thus, it is an appealing target for cancer treatment. Nanomedicine with targeting delivery ability has developed rapidly and shown its great therapeutic potential in cancer therapy. Proteins are ideal material for nanomedicine regarding to their excellent biocompatibility, and protein-only self-assembled nanoparticles technology provides a robust method to produce protein nanoparticles. Pro-apoptotic proteins or peptides, such as BAK, have attracted increasing attention in the inhibition of tumor growth. However, the self-assembled nanoparticles of BAK targeting to integrin αvβ3 over-expressed tumor cells need to be investigated. In this study, we designed recombinant proteins with BH3 BAK as active domain and RGD peptides as targeting ligands to self-assemble into protein nanoparticles (named as PN2-1 et al.), then experimentally evaluated the nanoparticle size, fluorescence feature, stability, targeting ability and cytotoxicity to tumor cells in vitro. The results showed that the protein nanoparticles containing RGD peptides had a uniform particle size with an diameter of approximately 23 nm. PN2-1 had notable inhibition to cell proliferation of C6 cells, C26 cells and MCF-7 cells, with a lower IC50 than the nanoparticles which only had BAK motif without RGD peptide. PN2-1 had higher cellular uptake into C6 cells than MCF-7 cells. Our results demonstrate that the RGD peptide could enhance the cytotoxicity of BAK nanoparticles to tumor cells and increase their tumor targeting ability. This study provides an insight into the design and development of integrin αvβ3 targeting protein nanoparticle for cancer treatment.

The liquefaction of tailings sand caused by seismic loads is a major problem for the safety of tailings ponds. Its liquefaction characteristics largely determine the stability of the dam. To study the flow characteristics of tailings sand after liquefaction under earthquake action, the flow characteristics of the tailings sand were liquefied by conducting a shaking table test. The flow equation is derived, and the discriminant factor of liquefaction flow is proposed. After liquefaction, the apparent viscosity in the tailings first decreases instantaneously, and then increases with the strain rate, but the apparent viscosity is almost unchanged. According to the experimental research of three types of seismic waves (Traft wave, El Centro wave, and Shanghai wave), the greater the ground motion amplitude is, the more obvious the shear thinning effect of the tailings sand and the more obvious the flow state. The proposed flow model is compared with the existing research results, which shows that the tailings sand is a fluid model after liquefaction and has good applicability. From the perspective of the relationship between the apparent viscosity and shear strain rate, the flow characteristics of saturated sand after liquefaction are studied, showing that the model is practical.

Clay reinforcement through appropriate applications of waste fiber or waste fiber fabric can generate huge economic and environmental benefits. In this study, clay was reinforced using waste polyester fiber filaments and waste polyester fabric blocks, respectively. Triaxial tests (σ1 > σ2 = σ3) were carried out to examine the influence of reinforcement method and the contents (0.0%, 0.5%, 1.0%, 1.5%) on the shear behavior of clay. After reinforcement, the deformation resistance and shear strength of the clay was improved. The optimal contents of fiber filament and fabric block were both 1.0%; as the fiber filament or fabric block content increased from 0.5% to 1.5%, the stiffness of the reinforced clay decreased, while the energy absorption capacity and the cohesive strength first increased and then decreased. Under the optimal content condition, the fiber filament showed better reinforcement than the fabric block. Under the train hardening condition, a hyperbolic model can be used to quantitatively describe the stress-strain relationship of the reinforced clay, and the model parameters can also reflect the strain hardening degree.

Integrin α

Rock burst is a catastrophic dynamic disaster caused by sudden failure and instability of coal, which brings threats to deep coal mining; the AE-charge signals and the fragment distribution are related to both mechanical properties of coal and disaster early warning directly. Hence, the variation of AE and charge induction during coal failure, fractal feature of coal fragments, and their relationship should be studied in depth. In this paper, uniaxial loading test was carried out for coal with bursting tendency samples produced by blocks cored from 800 m depth in Xiaoqing coal mine of the Tiefa Coal Group in northeast China; the fractal characteristics of specimens are obtained by using the statistical fractal method. The mechanics of similarities and differences between acoustic emission and charge signal is investigated by using loading experiments and theoretical analysis. It is found that the fragments of coal have good self-similarity properties; the fractal dimension of the specimens is in the range 2.085–2.521, the maximum range being 2.300–2.468, which is slightly higher than that of rock. The high-amplitude pulses of the acoustic emission and charge are concentrated in the macroscopic fissure development and expansion stage but they have asynchronous characteristics between them. The charge generation process is accompanied by the inhomogeneous deformation and sliding friction; the friction slip is the major one and is analysed theoretically. A theoretical model for the force-electric coupling relationship is established. The statistical results show that both the acoustic emission and the charge signal accumulation have a significantly proportional relationship with the fractal dimension. Both the acoustic emission and charge signal reveal coal breakage evolution process, which will help in obtaining the precursor information on coal failure. Furthermore, the monitoring results can predict the extent of coal mass instability.

Coal seam water injection technology which provides a guarantee for coal mine safety production is significant for the prevention and control of coal mine disasters. The selection of additives is very important for the implementation of coal seam water injection technology. Although the research on additives has been extensive in recent years, the mechanism of additives which can increase the permeability of coal and change mechanical properties of coal is still unclear. After selecting the chelating agent as the water injection additive, we characterized the pore structure of coal by low temperature N2 adsorption, mercury injection, scanning electron microscopy, etc., and tested the strength of coal by uniaxial hydraulic testing machine, as a result, several interesting results were found. Firstly, the minerals in the coal seam will damage the permeability of the coal seam and impede the flow of water in the coal seam. Secondly, the chelating ligand can interact with minerals like calcite and dolomite. When the concentration of the chelating agent is 500 mg/L, Ca2+ can be detected in the immersion solution and the leaching concentration of Ca2+ is 43.76 times greater than that in the ultra-pure water immersion solution. The change of pH has a greater impact on the leaching concentration of Fe and Mg, while the change of solid–liquid ratio has a smaller impact on their leaching concentration. Thirdly, as the dissolution of minerals, the size and volume of pore in coal increase, specific surface area decrease, connectivity of pore become better, the permeability of coal increase by an average of 129%, which has a promoting effect on water injection. Fourthly, the existence of minerals will affect the mechanical strength of coal. The uniaxial compressive strength of coal decreases after the chelating ligands interacted with the coal and the pH of the solution and soaking time also obviously affect the strength of coal. These results are helpful to open up a new direction for the selection of water injection additives that can realize the green and safe mining of coal.

When the rock burst occurs, energy absorption support is an important method to solve the impact failure. To achieve constant resistance performance of energy absorption device, as an important component of the support, the mechanical properties of one kind of prefolded tube is analyzed by quasi-static compression test. The deformation process of compression test is simulated by ABAQUS and plastic strain nephogram of the numerical model are studied. It is found that the main factors affecting the fluctuation of force-displacement curve is the stiffness of concave side wall. The original tube is improved to constant resistance by changing the side wall. The friction coefficient affects the folding order and form of the energy absorbing device. Lifting the concave side wall stiffness can improve the overall stiffness of energy absorption device and slow down the falling section of force-displacement curve. It is always squeezed by adjacent convex side wall in the process of folding, with large plastic deformation. Compared with the original one, the improved prefolded tube designed in this paper can keep the maximum bearing capacity ( Pmax), increase the total energy absorption ( E), improve the specific energy absorption (SEA), and decrease the variance ( S2) of force-displacement curve.

In this study, a series of triaxial tests was performed on a cemented sand improved by adding various contents of basalt fiber. The binding and interfacial interaction between the fiber and cemented sand matrix and the failure model of the interfacial interaction at the sliding surface were examined using scanning electron microscopy (SEM). The triaxial tests show that as the fiber content was increased, the cohesion and residual cohesion first increased and then decreased and the brittleness index decreased, whereas the internal friction angle and residual internal friction angle exhibited no clear variation patterns. Under the optimum fiber content of 0.75%, the cohesion is 406.1 kPa, and the residual cohesion is 145.4 kPa. Compared with cemented sand, the increase is 74.6% and 148.0%, respectively. The SEM tests show that the failure model of the interfacial interaction on the sliding surface included essentially the sliding and pull-out of fibers. The fiber was found to improve shear behavior through the interfacial effect and to affect the failure model through its bridging effect in binding sand particles.

The freeze-thaw cycle is one of the important factors in inducing a dam-break in the permafrost region, so it is of great practical significance to study the mechanism of the failure deformation of tailings dams under freeze-thaw cycles. In this paper, the water-heat-force coupling model of a tailings dam considering frost-thaw damage is established, and the freeze-thaw cyclic ageing deformation of a tailings dam in a seasonally frozen soil area is studied. The correctness of the model is validated by numerical calculation. The research shows under the same water content, the compressive strength and modulus of deformation decrease with an increase in the number of freeze-thaw cycles, the cohesion and internal friction angle decrease, and the amplitude gradually decreases before becoming stable. In the process of cooling, the pore water pressure first increases and then decreases, and the pore water pressure first decreases and then increases during the heating process. The research results can provide a theoretical basis and reference values for the stability analysis of tailings dams in seasonally frozen soil areas.

Discreteness of mechanical property affected by the intimal damage, which emerged with various degrees of material composition and geological structure, is the difference in porosity macroscopically. Although various porosities directly affect fracture activity, damage evolution and mechanical behaviour of coal bring on the bump-prone assessment error, and disaster happened “ahead of time” in deep underground energy source exploration, little research to date has focused on them. In this paper, the mechanical properties of bump-prone coal samples with different porosities were studied by uniaxial compression test and the initial damage caused by gangue and organic fracture in coal observed by CT. The result indicated that the evolution of coal strength and the logarithm of porosity were expressed by a linear negative correlation and the elastic modules decreased with the initial damage increased. A new quantitative description of damage variables is established by theoretical derivation to reflect the process of cracks formation and expiation in coal, based on volumetric strain and initial porosity. According to the Mohr–Coulomb principle, the effective stress of coal sample with higher the porosity is more likely to reach the shear strength and destruction. The amplitudes and accumulation of AE energy and charge pulse indeed vary with the stress loading stages and strength. The frequency of AE waveform is dominated in three bands (1∼50 kHz, 100∼150 kHz, and 175∼200 kHz) and that of charge induction had one frequency band 1∼100 Hz, and the amplitudes of time domain and main frequency components increased with stress improved. Both of them originated from cracks and belong to homologous signals, crack development bound to be accompanied by stress wavelet, not necessarily free charge; meanwhile, charge pulse being emerged means there must be cracks interaction and the acoustic emission signals are generated prior to charge induction.

In this study, the specimens of cemented sand were prepared by reinforcing it separately with different contents (0.5%, 1.0%, 1.5%, and 2.0%) of three different polymer fibers (polyamide, polyester, and polypropylene) prepared as filaments of different lengths (6, 9, and 12 mm). Then, these specimens were tested, and the improvement effects of the three fibers on the engineering-mechanical behavior of the cemented sand were analyzed and compared. The different microstructures and chemical compositions of the fiber-reinforced cemented sand specimens were investigated using electron microscopy and X-ray diffraction. Compression tests were performed to obtain the stress-strain curves of the specimens. Comparative analysis was performed on the variation patterns of the mechanical parameters (such as unconfined compressive strength and peak strain) of the specimens. Quantitative analysis was performed on the effect of fiber content and fiber filament length on the failure mode of the specimens. It was shown that the inclusion of fibers led to a change from brittle failure to ductile failure. The macro- and microexperimental results revealed that polypropylene fiber had the best improvement effect on the mechanical behavior of the cemented sand, followed by polyester fiber and polyamide fiber. In particular, the cemented sand specimen reinforced with 1.5% polypropylene fiber prepared as 9 mm length filaments had a brittleness index of 0.0578, exhibited ductile failure (in contrast to the brittle failure of the nonreinforced cemented sand), and yielded the highest unconfined compressive strength and shear strength among the specimens.

It has been a goal of artificial intelligence to make computers recognize objects and have the vision similar to human beings. After years of development, considerable progress has been made, but it is not satisfactory. It can be said that deep convolutional network is now the best algorithm for image recognition, which is also the reason why this paper decides to adopt deep convolutional network algorithm. The convolutional neural network USES Shared parameters between the convolutional layers, which not only reduces the required memory size, but also reduces the number of parameters to be trained and improves the performance of the algorithm. The difficulty of image recognition is hard to find a way to from the natural environment the boundary shape, texture, angular point, and image characteristics such as concept, and the image itself are highly susceptible to the influence of natural environment and changes in perspective, dimension, twist deformation, interference, light, shade, difficulties of the difference of background doping and within the class, make the computer more difficult to get about abstraction and understand the expression of natural images.

A simplified analytical solution is developed for estimating the thrusts and bending moments of the circular tunnel in half space under the obliquely incident SV wave. The seismic waves impinging on the tunnel is obtained according to the elastic wave motion theory in half space firstly, which is the superposition of the incident and reflected SV waves and reflected P wave. Then, by considering the tunnel lining as a thick-wall cylinder, analytical solutions for internal forces of circular tunnel due to the incident and reflected SV waves and the reflected P wave are deduced, which enables more precise forecasts than previous analytical solutions by the thin shell model. The total tunnel internal forces are obtained finally through the superposition of the above solutions under three kinds of waves. The accuracy of the proposed analytical solution is verified by comparing with the dynamic numerical results. Moreover, the discussion about the effect of critical factors on the accuracy of the proposed analytical solutions is conducted, including the tunnel structure inertia, the seismic wavelength, the lining thickness and the tunnel depth. These results demonstrate that the proposed analytical solution performs well and can be adopted to predict the internal forces of circular tunnel under obliquely incident SV wave in seismic design.

The evolution of the mechanical properties of rock as a function of thermal damage is relevant to various engineering applications, such as nuclear waste repositories, underground coal gasification, dry-fracture shale system and geothermal energy extraction. The thermal properties of heterogeneous rock control heat transmission with differential thermal expansion potentially resulting in significant changes in the mechanical and transport behavior of reservoir rocks. We define a novel dual-damage thermal-mechanical model accommodating the interaction of thermal conductivity, thermally-induced deformation, rock mechanical deformation and damage to define the evolution of the thermal and mechanical properties of rock during thermal treatment. Importantly, the dual-damage constitutive model is capable of using elastic modulus and strength to solve for asynchronous changes in peak strain and peak strength, respectively. The proposed model is validated against analytical solutions and laboratory data. The results indicate that thermally-induced damage increases rock porosity and permeability while simultaneously decreasing elastic modulus and strength. Thermal treatment causes a realignment in the rock microstructure and results in a change in the ultimate failure pattern. Thermally-induced damage causes irreversible increases in rock porosity and permeability even as temperature is restored. Furthermore, it is confirmed that thermally-induced damage in rock is dominated by the type of tensile damage during the thermal expansion. The proposed dual-damage constitutive model better explains the non-proportional relationship between peak strength and peak strain observed in many experiments.

The rational use of drilling parameters is a hot issue in the field of geotechnical engineering and geological engineering. A new method, for evaluating the bearing capacity of soils using drilling parameters was proposed. First, through the mechanical analysis of the drill bit, the preconditions and theoretical formulas for calculating the bearing capacity of soils using the bit’s torque are clearly defined. Next, drilling tests and dynamic cone penetration tests were performed on miscellaneous fill, silty clay, sandy clay, medium coarse sand and gravel sand, and the empirical formula for calculating the bearing capacity of these soils were given. Then, using the new method and the empirical formula, the bearing capacity of the soil under the roadbed was examined. The test results show that the bit’s torque is a good parameter for the evaluation of the bearing capacity of the soil. Finally, the application scope of the new method and the empirical formula is discussed, and the subsequent research directions are pointed out.

In this study, based on the mining of the 13210 working face in the Yima coal mine of the Gengcun village, China, a simplified mechanical model for the analysis of dynamic destabilization of the overlying strata during underground mining was constructed. The numerical simulation was used to analyze the stress patterns in the advanced abutments of the tunnel face and the characteristics of dynamic failures in the overlying strata. Furthermore, similitude experiments were conducted to study the process of stress release and deformation in the overlying strata, and to analyze the effects of overburden destabilization on the ground surface settlement. The theoretical analysis indicated that if the geometric parameters of a working face are fully determined, a stiffness ratio no greater than 1 is required for dynamic destabilization to occur. The numerical simulation results show that the stress in the overlying strata decreases with a decrease in distance from the tunnel face. The stresses in the advanced abutments initially increase with an increase in distance from the tunnel face, followed by a decrease in stress, and an eventual stabilization of the stress levels; this corresponds to the existence of a “stress build-up zone,” “stress reduction zone,” and “native rock stress zone.” In similitude experiments, it was observed that a “pseudoplastic beam” state arises after the local stresses of the overlying strata have been completely released, and the “trapezoidal” fractures begin to form at stress concentrations. If the excavation of the working face continues to progress, the area of collapse expands upward, thereby increasing the areas of the fracture and densification zones. Owing to the nonuniform settlement of the overlying strata and the continuous development of bed-separating cracks, secondary fractures will be generated on both sides of the working face, which increase the severity of the ground surface settlement.

The stability of water-filled dump slope has been one significant geotechnical engineering problem that needs to be urgently resolved. The coupling effects of seepage and damage on the dump slope are critically important for stability analysis. In this paper, a seepage-damage coupled mathematical model is developed for fractured coal rock mass, and the permeability tensor effects from the fracture damage of coal rock mass are investigated. Numerical simulations are conducted for Dongming and Heidaigou dump slope on the stability of water-filled dump slope under the coupling effects of seepage and damage. Numerical results show that the high pore pressure can reduce the positive pressure of the sliding surface and the friction, and can lead to the strength loss of water-filled coal rock mass. It is also demonstrated that with the propagation of the slope crack, the pore pressure gradually dissipate to larger areas, and approaches the slope table. This will result in the further damage of the table rock of slope and the decrease of support force, has a serious impact on the overall slope stability of the system. With the development of seepage, the opened cracks increase gradually. The water pressure not only has restructured the fracture network of coal rock, but also has a huge impact on the main fracture deformation. It is demonstrated that if pore water pressure is difficult to dissipate, effective stress decreases and weak surface increases, and this further leads to instability of coal rock slope. The results also reveal that it is easy to cut out at the foot of the slope. Two failure models of "arc" or "located-sliding" are observed. The numerical results further reveal the percolation mechanism of the softening of coal rock slope. (C) 2013 Elsevier Ltd. All rights reserved.

The interface barrier formation mechanism of micro-cracks of coal and rock mass is investigated by using theoretical analysis and piezoelectric experiments. It is found that the micro-cracks of coal or rock expand constantly under external loads, while the slip, dislocations and inhomogeneous deformation of crack interface and lattice cause charge breakthrough, and then, barrier form on the crystal interface. The generation process of charge is accompanied by the friction of micro-crack slip, and the dislocation and deformation are analyzed theoretically. A theoretical model of micro-crack slip friction charge is established. Furthermore, piezoelectric law of coal or rock deformation and fracture is studied experimentally. The results show that cracks expand vertically more seriously than horizontally, and vertical cracks expand first, followed by horizontal ones, which expand continuously till crashed at the end of the coal sample. Crack interface value of potential barrier increases constantly in the compression process of coal sample. And before the coal sample gets crashed, sliding friction between crack interfaces reaches the peak, together with the potential barrier. Moreover, extreme acceleration of transfer speed of charge is based on extreme multiplying potential value of crack interface. Both crack interface barrier and potential amplitude get change dramatically before the coal sample fracture, which will help to get the precursor information of coal sample rupture. More importantly, the monitoring results can predict the extent and state of coal and rock rupture.