Pre-stressed bolt anchorage is the key technology for jointed rock masses in rock tunnelling, slope treatment and mining engineering. To investigate the mechanical properties and reinforcement effect of jointed rock masses with pre-stressed bolts, in this study, uniaxial compression tests were conducted on specimens with different anchoring types and flaw inclination angles. ABAQUS software was used to verify and supplement the laboratory tests. The laws of the uniaxial compressive strength (UCS) obtained from the numerical simulations and laboratory tests were consistent. The results showed that under the same flaw angle, both the UCS and elastic modulus of the bolted specimens were improved compared with those of the specimens without bolts and the improvements increased with an increase in the bolt pre-stress. Under the same anchoring type, the UCS and elastic modulus of the jointed specimens increased with an increase in the flaw angle. The pre-stressed bolt could not only restrain the slip of the specimens along the flaw surface but also change the propagation mode of the secondary cracks and limit the initiation of cracks. In addition, the plot contours of the maximum principal strain and the Tresca stress of the numerical models were influenced by the anchoring type, flaw angle, anchoring angle and bolt position.

It is of great significance for safety reason to obtain the triaxial compressive properties of cemented tailings backfill(CTB). The influence of cement content, curing age and confining pressure on strength and deformation properties of CTB was examined and discussed. Results indicate that the triaxial compressive and deformation behavior of CTB is strongly affected by the cement content, curing age and confining pressure. The increase in cement content, curing age and confining pressure leads to a change in stress-strain behavior and an increase in the axial strain at failure and post-peak strength loss. The cohesion of CTB rises as the curing age and cement content increase. However, the enhancement in internal friction angle is trivial and negligible. It should be noted that the failure pattern of CTB samples in triaxial compression is mainly along a shear plane, the confining pressure restrains the lateral expansion and the bulging failure pattern is dominantly detected in CTB samples as curing age length and cement content increase. The results will help to better understand the triaxial mechanical and deformation behavior of CTB.

The stability control of surrounding rock for large or super-large section chamber is a difficult technical problem in deep mining condition. Based on the in-site geological conditions of Longgu coal mine, this paper used the dynamic module of FLAC^3D to study the response characteristics of deep super-large section chamber under dynamic and static combined loading condition. Results showed that under the static loading condition, the maximum vertical stress, deformation and failure range are large, where the stress concentration coefficient is 1.64. The maximum roof-to-floor and two-sides deformations are 54.6 mm and 53.1 mm, respectively. Then, under the dynamic and static combined loading condition: (1) The influence of dynamic load frequency on the two-sides is more obvious; (2) The dynamic load amplitude has the greatest influence on the stress concentration degree, and the plastic failure tends to develop to the deeper; (3) With the dynamic load source distance increase, the response of surrounding rock is gradually attenuated. On this basis, empirical equations for each dynamic load conditions were obtained by using regression analysis method, and all correlation coefficients are greater than 0.99. This research provided reference for the supporting design of deep super-large section chamber under same or similar conditions.

A large amount of acid-leaching residue is produced during the conventional Zn hydrometallurgy process, and this residue has a large concentration of a variety of valuable metals. The purpose of this study was to evaluate the ability of a procedure that entails the use of sulfation roasting, water leaching, and chlorination leaching (blowing oxygen technique) to recover Pb and Ag, followed by cooling crystallization and the replacement of Ag with lead sheet, to realize the full recovery of all valuable metals from zinc acid-leaching residue; consequently, good results were achieved. The best results were obtained under the following conditions: a sulfuric acid at 70% of the raw material quality, roasting temperature of 300 °C and roasting time of 2 h, followed by the process of leaching the roasted residue for 1 h by applying a water-to-solid ratio of 5:1 at room temperature. The recovery rates of Zn and Fe were 98.69% and 92.36%, respectively. The main parameters of the chlorine salt leaching system were as follows: Cl⁻ concentration of 300 g/L, Fe³⁺ concentration of 25 g/L, acid concentration of 2 mol/L, liquid-to-solid ratio of 9 mL:1 g, temperature of 90 °C, and leaching time of 0.5 h; this leaching process was followed by filtration separation. These conditions resulted in high extents of leaching for Pb and Ag (i.e., 98.87% and 96.74%, respectively). Finally, the kinetics of the process of Ag leaching using Cl⁻ ions in an oxygen-rich medium was investigated. It was found that the leaching process was controlled by the diffusion of the product layers, and the activation energy was 19.82 kJ/mol.

The method to fluorinate the terminal group has achieved remarkable success and been widely used to fine-tune the intrinsic properties of organic acceptor materials. Referring to chlorination, however, it gets less attention and remains ambiguous effect on organic photovoltaic (OPV) cells. Herein, a new non-fullerene acceptor named Y19 was reported with benzotriazole as the electron-deficient core and 2Cl-ICs as the strong electron-withdrawing end groups. Y19 exhibits a wide film absorption band from 600 nm to 948 nm and low LUMO (the lowest unoccupied molecular orbital) energy level of −3.95 eV Photovoltaic devices based on PM6:Y19 show high-power conversion efficiency (PCE) of 12.76 % with high open-circuit voltage (V_oc) of 0.84 V, short-circuit current density (J_sc) of 22.38 mA/cm² and fill factor (FF) of 68.18 %. Broad external quantum efficiency (EQE) response of over 60 % in the range of 480–860 nm can be obtained. This study demonstrates that chlorination, as a low-cost molecular design strategy, has its own superiorities to improve device performance and promote the potential application in OPV.

Under various electromagnetic induction heating powers, different Al₃Ti/Al composites were fabricated by in-situ synthesis method from aluminum and titanium fibers. Microstructures and particles distribution of the composites were examined by XRD, SEM and EDS. The results show that no other intermetallic compounds beside Al₃Ti can be in-situ synthesized. Around the titanium fibers, the reaction zones and diffusion zones can be obviously found. Due to the stirring of the electromagnetic function, the formation of the micro-cracks inside the reaction zone was conducive to the peeling off of the Al₃Ti particles, and ensures the continuous reaction between liquid aluminum and titanium fibers, as well as the diffusion of Al₃Ti particles. At the same time, there were secondary splits of Al₃Ti particles located in diffusion zones. Two-body abrasion test shows that with the increase of induction heating power, the wear rates of the composites reduced and the number of grooves decreased.

Activated carbon (AC) particles sandwiched reduced graphene oxide sheets (rGO) film has been successfully fabricated via a facile self-assemble approach. The as-formed AC/rGO film is self-standing, flexible and mechanically robust, allowing to be transferred to any substrate on demand without rupture. Since AC particles effectively suppressed the restacking of the rGO sheet, AC/rGO film exhibits loose layer-by-layer stacking structures with various gaps between AC particles and rGO sheets, which is different from compact structures of pure graphene films. The as-formed gaps provide fast diffusion channels for electrolyte ions and enhanced accessible surface area of rGO. Therefore, the AC/rGO electrode delivers improved electrochemical performance over the voltage range of 0.0—3.0 V. This work offers a promising strategy to design free-standing supercapacitor electrodes based on traditional nanocarbon materials.

Ni-P/SiC/PTFE coating was obtained on the surface of 316L stainless steel by electrodeposition of Ni-P/SiC coating and immersion of PTFE (polytetrafluoroethylene). The surface morphology and composition were analyzed by scanning electron microscope and energy dispersive spectrometer. The corrosion resistance of the coating in 0.5 mol/L H₂SO₄+2×10⁻⁶ HF solution was studied by electrochemical method. Surface contact angle was used to test the hydrophobic properties of the coating. The results indicated that the Ni-P/SiC/PTFE coating prepared on the surface of stainless steel was uniform and compact, which significantly improved the self-corrosion potential of stainless steel. The self-corrosion current density decreased from 7.62 to 0.008 µA/cm². The durability performance of coating was tested under 0.6 V voltage and the stable corrosion current density value was 0.19 µA/cm², then wetting angle was tested after durability experiment and the value is 134.5 °.

Hexagonal porous Nb₂O₅ was synthesized for the first time via a facile solid-state reaction. The structure and electrochemical properties have been optimized through tuning heating temperature. X-ray diffraction results indicate that pseudo hexagonal Nb₂O₅ (TT-Nb₂O₅) and orthorhombic Nb₂O₅ have been synthesized at different temperatures. Hexagonal sheet and porous structure of Nb₂O₅ were characterized by scanning electron microscopy and N₂-adsorption-desorption isotherms. The as-prepared TT-Nb₂O₅ (heated at 600 °C) shows the best performance with a remarkable charge capacity of 178 mA·h/g at 0.2C, which is higher than that of T-Nb₂O₅. Even at 20C, TT-Nb₂O₅ offers unprecedented rate capability up to 86 mA·h/g. The high rate capacity is due to pseudocapacitive Li⁺ intercalation mechanism of TT-Nb₂O₅. The reported results demonstrate that Nb₂O₅ with good crystal structure and high specific surface area is a powerful composite design for high-rate and safe anode materials.

TiN, which is ubiquitous in Ti-bearing steel, has a critical influence on both the mechanical properties and the welding process of steel, and therefore researche on the precipitation behavior of TiN in molten steel bath is of great significance. In this paper, Ti-bearing peritectic steel was taken as the study object and FactSage was adopted to explore how the precipitation behavior of typical inclusions in steel was affected by the steel composition. Furthermore, microsegregation models were used to analyze the precipitation process of TiN at solidification front, and the calculation results were finally verified by scanning electron microscope (SEM). Research showed that a multitude of dispersed particles of high melting oxide MgAl₂O₄ or MgO always existed in molten steel after magnesium treatment. In consideration of the segregation and enrichment of solute elements at the solidification front, the Ohnaka microsegregation model was employed to compute the precipitation during solidification. In the event of the solid fraction reaching 0.95 or more, the concentration product of [Ti][N] at the solidification front exceeded the equilibrium concentration product, then TiN began to precipitate. MgO or MgAl₂O₄ cores were generally found in TiN particles of peritectic steel after the magnesium treatment, which was consistent with the thermodynamic calculation results. Moreover, the average size of TiN particles was reduced by approximately 49%. This demonstrated that Mg-rich high melting inclusions were formed after the magnesium treatment, by which the heterogeneous nucleation of TiN was promoted it; therefore, favorable nucleation sites were provided for further refining the high-temperature ferrite phase.

In order to solve the problem of pressure shock on the continuous rotary electro-hydraulic servo motor, the mathematical models of pressure gradient under the structure of pre-compressed chamber and U-shaped groove were established. The optimal structure dimensions of the pre-compressed chamber and the U-shaped groove were determined. The fluid models were established by Solidworks under the four structures of triangular groove, triangular groove with pre-compression chamber, U-shaped groove and U-shaped groove with pre-compression chamber. Simulation analysis of depressurization process of fluid models was performed based on FLUENT. The pressure nephograms of different buffer structures were compared and analyzed, and the pressure change curves and pressure gradient change curves in the process of depressurization were obtained. The results show that the optimal edge length of the pre-compressed chamber of continuous rotary electro-hydraulic servo motor is 20 mm in the process of decompression. The pressure reduction effect is the best when the width of the U-shaped groove is 1.5 mm and the depth is 1.65 mm. The U-shaped groove structure with pre-compression chamber is more conducive to alleviate the pressure shock phenomenon of the motor compared with different combine buffer structures.

The investigation was carried out on the technical problems of finishing the inner surface of elbow parts and the action mechanism of particles in elbow precision machining by abrasive flow. This work was analyzed and researched by combining theory, numerical and experimental methods. The direct simulation Monte Carlo (DSMC) method and the finite element analysis method were combined to reveal the random collision of particles during the precision machining of abrasive flow. Under different inlet velocity, volume fraction and abrasive particle size, the dynamic pressure and turbulence flow energy of abrasive flow in elbow were analyzed, and the machining mechanism of particles on the wall and the influence of different machining parameters on the precision machining quality of abrasive flow were obtained. The test results show the order of the influence of different parameters on the quality of abrasive flow precision machining and establish the optimal process parameters. The results of the surface morphology before and after the precision machining of the inner surface of the elbow are discussed, and the surface roughness R_a value is reduced from 1.125 µm to 0.295 µm after the precision machining of the abrasive flow. The application of DSMC method provides special insights for the development of abrasive flow technology.

A dynamic model of a flexible rotor supported by ball bearings with rubber damping rings was proposed by combining the finite element and the mass-centralized method. In the proposed model, the rotor was built with the Timoshenko beam element, while the supports and bearing outer rings were modelled by the mass-centralized method. Meanwhile, the influences of the rotor’s gravity, unbalanced force and nonlinear bearing force were considered. The governing equations were solved by precise integration and the Runge-Kutta hybrid numerical algorithm. To verify the correctness of the modelling method, theoretical and experimental analysis is carried out by a rotor-bearing test platform, where the error rate between the theoretical and experimental studies is less than 10%. Besides that, the influence of the rubber damping ring on the dynamic properties of the rotor-bearing coupling system is also analyzed. The conclusions obtained are in agreement with the real-world deployment. On this basis, the bifurcation and chaos behaviors of the coupling system were carried out with rotational speed and rubber damping ring’s stiffness. The results reveal that as rotational speed increases, the system enters into chaos by routes of crisis, quasi-periodic and intermittent bifurcation. However, the paths of crisis, quasi-periodic bifurcation, and Hopf bifurcation to chaos were detected under the parameter of rubber damping ring’s stiffness. Additionally, the bearing gap affects the rotor system’s dynamic characteristics. Moreover, the excessive bearing gap will make the system’s periodic motion change into chaos, and the rubber damping ring’s stiffness has a substantial impact on the system motion.

In order to track the desired path as fast as possible, a novel autonomous vehicle path tracking based on model predictive control (MPC) and PID speed control was proposed for high-speed automated vehicles considering the constraints of vehicle physical limits, in which a forward-backward integration scheme was introduced to generate a time-optimal speed profile subject to the tire-road friction limit. Moreover, this scheme was further extended along one moving prediction window. In the MPC controller, the prediction model was an 8-degree-of-freedom (DOF) vehicle model, while the plant was a 14-DOF vehicle model. For lateral control, a sequence of optimal wheel steering angles was generated from the MPC controller; for longitudinal control, the total wheel torque was generated from the PID speed controller embedded in the MPC framework. The proposed controller was implemented in MATLAB considering arbitrary curves of continuously varying curvature as the reference trajectory. The simulation test results show that the tracking errors are small for vehicle lateral and longitudinal positions and the tracking performances for trajectory and speed are good using the proposed controller. Additionally, the case of extended implementation in one moving prediction window requires shorter travel time than the case implemented along the entire path.

Necking defects have long troubled the application of cross-wedge rolling technology in aluminium alloy shaft parts. To accurately predict necking defects, new judgement conditions are established based on the thermal performance of 6082 aluminium alloy. The limit-sectional shrinkage without necking defects is achieved by combining theoretical calculation and finite-element model analysis, which couples heat transfer and deformation. In this paper, a 6082 aluminium alloy extruded rod with a 40 mm diameter rolled at a preheated temperature of 500 °C and a rolling angular velocity of 1 rad/s is taken as an example. The simulation and experimental results show that necking defects do not occur on the rolled pieces if the sectional shrinkage is below the limit-sectional shrinkage but will occur when the sectional shrinkage is above it. The results prove that the prediction model of necking defects in cross-wedge rolling of 6082 aluminum alloy is feasible, and this research provides a theoretical basis for the qualified aluminum alloy shafts produced by the cross-wedge rolling.

In order to meet the precision requirements and tracking performance of the continuous rotary motor electro-hydraulic servo system under unknown strong non-linear and uncertain strong disturbance factors, such as dynamic uncertainty and parameter perturbation, an improved active disturbance rejection control (ADRC) strategy was proposed. The state space model of the fifth order closed-loop system was established based on the principle of valve-controlled hydraulic motor. Then the three parts of ADRC were improved by parameter perturbation and external disturbance; the fast tracking differentiator was introduced into linear and non-linear combinations; the nonlinear state error feedback was proposed using synovial control; the extended state observer was determined by nonlinear compensation. In addition, the grey wolf algorithm was used to set the parameters of the three parts. The simulation and experimental results show that the improved ADRC can realize the system frequency 12 Hz when the tracking accuracy and response speed meet the requirements of double ten indexes, which lay foundation for the motor application.

As a new neural network model, extreme learning machine (ELM) has a good learning rate and generalization ability. However, ELM with a single hidden layer structure often fails to achieve good results when faced with large-scale multi-featured problems. To resolve this problem, we propose a multi-layer framework for the ELM learning algorithm to improve the model’s generalization ability. Moreover, noises or abnormal points often exist in practical applications, and they result in the inability to obtain clean training data. The generalization ability of the original ELM decreases under such circumstances. To address this issue, we add model bias and variance to the loss function so that the model gains the ability to minimize model bias and model variance, thus reducing the influence of noise signals. A new robust multi-layer algorithm called ML-RELM is proposed to enhance outlier robustness in complex datasets. Simulation results show that the method has high generalization ability and strong robustness to noise.

This paper proposes a novel reconfigurable Goldberg 6R linkage, conformed to the construction of variant serial Goldberg 6R linkage, while simultaneously satisfying the line-symmetric Bricard qualifications. The isomeric mechanism of this novel reconfigurable mechanism is obtained in combination with the isomerization method. The geometrically constrained conditions result in variable motion branches of the mechanism. Based on the singular value decomposition of the Jacobian matrix, the motion branches and branch bifurcation characteristics are analyzed, and the schematics of bifurcations in joint space is derived. This novel 6R linkage features one Goldberg 6R motion branch, two line-symmetric Bricard 6R motion branches, and one Bennett motion branch. With regards to the line-symmetric Bricard 6R motion branches, a similar function for the disassembly and recombination process can be achieved by reconstructing an intermediate configuration through bifurcation. Then, the isomerized generalized variant Goldberg 6R linkage is explicated in a similar way. Acting as a bridge, reconfigurability connects two families of overconstrained mechanisms.

In order to deal with the complex association relationships between classes in an object-oriented software system, a novel approach for identifying refactoring opportunities is proposed. The approach can be used to detect complex and duplicated many-to-many association relationships in source code, and to provide guidance for further refactoring. In the approach, source code is first transformed to an abstract syntax tree from which all data members of each class are extracted, then each class is characterized in connection with a set of association classes saving its data members. Next, classes in common associations are obtained by comparing different association classes sets in integrated analysis. Finally, on condition of pre-defined thresholds, all class sets in candidate for refactoring and their common association classes are saved and exported. This approach is tested on 4 projects. The results show that the precision is over 96% when the threshold is 3, and 100% when the threshold is 4. Meanwhile, this approach has good execution efficiency as the execution time taken for a project with more than 500 classes is less than 4 s, which also indicates that it can be applied to projects of different scales to identify their refactoring opportunities effectively.

The purpose of this study was to examine the sedimentary facies characteristics of lower Cambrian Niutitang Formation (∈₁n) in South China, to reveal the mechanism of organic matter enrichment, and to guide exploration of shale gas. Macro investigation and experimental analyses were used to assess the lithology in detail, total organic matter mass fraction w(TOC), mineral composition, and trace element characteristics of ∈₁n. The influencing factors of organic matter enrichment were discussed extensively, and a sedimentary facies mode was suggested. In the early stage of ∈₁n, the locations of Well E’yangye 1, Well Ciye 1, Well Changye 1, and Well Anye 1 respectively develop, platform inner sag, outer shelf, Jiangnan slope belt, and South China detention basin. In the late stage of ∈₁n, the sedimentary facies evolve with decreasing sea level. The study area presents a complete three-step basin in the Early Cambrian. In the early stage of ∈₁n, the first step is the Yangtze carbonate platform, the second step is the outer shelf and slope, and the third step is the deep-water basin. From the Yangtze carbonate platform to the deep-water basin, w(TOC) and the mass fraction of quartz gradually increase, the mass fraction of carbonate mineral decreases, and the mass fraction of clay mineral is higher in the second step. The sea level fluctuation results in a higher w(TOC) vertically in the lower ∈₁n shale, and the paleogeographic (provenance) conditions lead to better horizontal development of organic matter in the outer shelf, slope and detention basin. Trace elements are abundant in the lower ∈₁n, and w(TOC) is correlated positively with many trace elements. In the outer shelf, slope, and adjacent areas, hydrothermal activity and upwelling current bring nutrient-rich material and promote organic matter enrichment under a strong reducing condition. Deep-shelf, slope and deep-water basin are the best facies for the formation and preservation of organic matter, especially deep-water basin facies. It remains necessary to strengthen the exploration of shale gas in the deep-water basin of ∈₁n in central Hunan, China.

Asphalt mixture pavement reheating is one of the important steps in hot in-place recycling (HIR). To improve the heating speed of asphalt pavement in HIR, based on the numerical analysis model of asphalt mixture heating process, a new multi-layer low-temperature heating method (MLHM) was proposed. Considering input heat flux, the thermal capacity and thermal resistance of asphalt mixture, the heat transfer model was established based on energy conservation law. By heating the asphalt mixture in layers, it changes the situation that the heat energy can only be input from the upper surface of the asphalt mixture pavement. Through the simulation of the heating method of asphalt mixture in the existing technology, the result shows that the existing heating methods lead to serious aging or charring of the asphalt mixture. By MLHM, the upper and the bottom of the asphalt mixture are heated at the same time, and the heating temperature is lower than other heat methods, which not only reduces the heating thickness and increases the heating area of the asphalt mixture pavement, but also improves the heating speed, saves the energy resource and ensures the heating quality. Especially, by MLHM, the heating uniformity is better and speed is faster.

Fibre-reinforced polymer (FRP) has the advantages of high strength, light weight, corrosion resistance and convenient construction and is widely used in repairing and strengthening damaged concrete columns. Most of the existing strength models were built by regression analysis of experimental data; however, in this article, a new unified strength model is proposed using the Hoek-Brown failure criterion. To study the strength of FRP-confined damaged and undamaged concrete columns, 900 test data were collected from the published literature and a large database that contains the cross-sectional shape of each specimen, the damage type, the damage level and the FRP-confined stiffness was established. A new strength model using the Hoek-Brown failure criterion was established and is suitable for both circular and square columns that are undamaged, load-damaged and fire-damaged. Based on the database, most of the existing strength models from the published literature and the model proposed in this paper were evaluated. The evaluation shows that the proposed model can predict the compressive strength for FRP-confined pre-damaged and undamaged concrete columns with good accuracy.

This study aims to evaluate the performance of silica fume (SF) and nano-silica (NS) on enhancing the sulfuric acid resistance of mortar mixtures. The NS and SF were added as substitutions for cement at various dosages. The cured samples were immersed in the sulfuric acid solution with a pH of 2 for 75 d. A compressive strength test and absorption and voids tests were conducted before sulfuric acid immersion. It was found that the addition of SF and NS reduced the volume of permeable voids and increased compressive strength. A thermo-gravimetric analysis was carried out to investigate the hydration of mixtures. The mixtures with SF showed a higher level of pozzolanic reaction compared with mixtures with NS. After the 75 d of immersion, the mixtures with 5% SF and 1% NS showed the best resistance against sulfuric acid because they showed the lowest mass change and length change.

Considering both the compaction effect of pile surrounding soil and the stress diffusion effect of pile end soil, this paper theoretically investigates the torsional vibration characteristics of tapered pile. Utilizing the complex stiffness transfer model to simulate compaction effect and tapered fictitious soil pile model to simulate stress diffusion, the analytical solution for the torsional impedance at tapered pile top is obtained by virtue of Laplace transform technique and impedance transfer method. Based on the present solution, a parametric study is conducted to investigate the rationality of the present solution and the influence of soil and pile properties on the torsional vibration characteristics of tapered pile embedded in layered soil. The results show that, both the compaction effect and stress diffusion effect have significant influence on the torsional vibration characteristics of tapered pile, and these two factors should be considered during the dynamic design of pile foundation.

For the Guanshui Road Station tunnel project of Guiyang Metro Line 2, the wind pavilion group was moved out of the main tunnel to reduce the number of openings in the main tunnel, and the wind pavilion group was excavated in a triangular configuration at the entrance of the main tunnel. Based on the finite element software ABAQUS, a three-dimensional model is established to study the influence of different triangular-distribution tunnels excavation schemes on the surface settlement and tunnel stability. The objective of this study is to reveal the change rules of surface settlement, deformation and force in the support structures and the surrounding rock and identify the best excavation scheme for this tunnel configuration. Results show that to control the surface settlement and the deformation of the support structures, the optimal excavation sequence involves excavating the upper fresh air exhaust tunnel before the lower running tunnel. To control the stress of the support structures, the optimal excavation involves excavating the lower running tunnel before the upper fresh air exhaust tunnel. In this project, the most reasonable excavation sequence of the tunnel is from top to bottom. The most reasonable thickness of tunnel penetration is 5 m.

The fracture initiation behavior for hydraulic fracturing treatments highlighted the necessity of proposing fracture criteria that precisely predict the fracture initiation type and location during the hydraulic fracturing process. In the present study, a Mohr-Coulomb criterion with a tensile cut-off is incorporated into the finite element code to determine the fracture initiation type and location during the hydraulic fracturing process. This fracture criterion considers the effect of fracture inclination angle, the internal friction angle and the loading conditions on the distribution of stress field around the fracture tip. The results indicate that the internal friction angle resists the shear fracture initiation. Moreover, as the internal friction angle increases, greater external loads are required to maintain the hydraulic fracture extension. Due to the increased pressure of the injected water, the tensile fracture ultimately determines the fracture initiation type. However, the shear fracture preferentially occurs as the stress anisotropy coefficient increases. Both the maximum tensile stress and equivalent maximum shear stress decrease as the stress anisotropy coefficient increases, which indicates that the greater the stress anisotropy coefficient, the higher the external loading required to propagate a new fracture. The numerical results obtained in this paper provide theoretical supports for establishing basis on investigating of the hydraulic fracturing characteristics under different conditions.

In this paper, organic montmorillonite (OMMT) was added into crumb rubber modified asphalt (CRMA) to improve its high temperature performance, anti-aging performance and storage stability. The effects of different OMMT content on properties of CRMA were studied. The rutting factor obtained by dynamic shear rheological (DSR) test was adopted to evaluate the high-temperature performance. The creep stiffness and m value determined by the bending beam rheometer (BBR) test were employed to evaluate the low-temperature performance. The softening point, ductility, rutting factor before and after rolling thin film ovens test (RTFOT) and pressure aging vessel test (PAV) were compared to characterize the aging properties. Moreover, the segregation test after being reserved for 48 h and 7 d was conducted, and the softening point and rutting factor of upper and lower layers of segregation pipe were adopted to evaluate the storage stability. The results indicated that the high-temperature performance and anti-aging performance were developed with the increasing content of OMMT, while the low-temperature performance deteriorated. The storage stability was improved with the increasing content of OMMT before the content exceeded 4%, after which the storage stability declined. Taking account of all factors, it is suggested that the optimum content of OMMT is 3%–4%.