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The microscopic parameters in the numerical method have an important influence on the results and computational efficiency of the models. The existing calibration methods of microscopic parameters in the finite-discrete element method (FDEM) are based on two-dimensional (2D) FDEM model, and there is a lack of calibration methods for microscopic parameters suitable for three-dimensional (3D) FDEM model. Therefore, this paper proposes a fast and convenient calibration method for the microscopic parameters of the 3D FDEM model. First, a tangential contact force calculation algorithm based on the total normal force is proposed and verified by the slider model. Subsequently, assuming that the penalty parameter of the solid element is equal to the penalty parameter of the joint element, the relationship between the normal penalty parameter and the tangential penalty parameter, and the relationship between the normal penalty parameter and the Young's modulus are studied using several numerical models. Moreover, the tensile strength and crack propagation path of the Brazilian disc model under different fracture energy parameter combinations are studied, and the fracture energy parameters are calibrated. Then, the triaxial compression model under different confining pressures is used to calibrate the cohesion c and the internal friction angle φ. In addition, the effects of loading rate, mesh size and time step on the model strength and calculation time are considered, respectively. Finally, the numerical simulation of dynamic Brazilian splitting test is carried out to verify the reliability of the parameter calibration method proposed in this paper. Although the calibration method of microscopic parameters is not unique, the microscopic parameter calibration method has important reference significance and is conducive to the application of 3D FDEM model. Highlights: A tangential contact force calculation algorithm based on the total normal contact force is proposed and verified by the slider model. The tangential penalty parameter in the 3D FDEM model needs to be greater than the normal penalty parameter, and the threshold of the normal penalty parameter is 50 times Young 's modulus. The tensile strength of the Brazilian disc model always begins to converge when the fracture energy GII is equal to 10GI, and the crack propagation path is along the central diameter direction. [ABSTRACT FROM AUTHOR]

To investigate the asymmetric failure mechanism and failure mode of layered rock tunnels, a novel mixed-mode power exponent cohesive zone model (M-PECZM) is proposed in this paper, which can capture the crack propagation process under single-mode loading, tension-shear loading, and compression-shear loading conditions. The parameters in the formula can be obtained from pure tensile and shear tests, and the introduction of the post-peak characteristic parameter α makes the M-PECZM suitable for post-peak softening curves of different kinds of rocks. The proposed M-PECZM is embedded in FDEM to carry out uniaxial compression, direct tension, and triaxial compression simulations. By comparison, the numerical and experimental results show a good agreement, which verifies the reliability and effectiveness of the M-PECZM. Besides, the FDEM is adopted to simulate the excavation of gently inclined layered surrounding rock tunnel, and the influence of shear stress field and buried depth on the EDZ evolution process and convergence displacement is studied. Highlights: A novel mixed-mode power exponent cohesive zone model (M-PECZM) for FDEM is proposed. The introduction of the post-peak characteristic parameter α makes the M-PECZM suitable for various rocks. Comparisons with experiments verify the accuracy and completeness of the M-PECZM. The influence of shear stress field and buried depth on the EDZ evolution process and convergence displacement is analyzed particularly. The asymmetrical deformation mechanisms of the tunnel resulted from the coupling action between the layered soft rock and tectonic shear stress. [ABSTRACT FROM AUTHOR]

Floor heave is a disaster that is frequently encountered in tunnel engineering. Existing explanations of floor heave mechanisms have many limitations, and the most important of which is that the stress concentration, release and transfer phenomena and the influences of the in-situ stress lateral coefficient and tensile strength are ignored. Therefore, the combined finite-discrete element method (FDEM) is used to study the failure process of floor rock masses and propose a new mechanical mechanism of floor heave that can consider the influences of the in-situ stress lateral coefficient and tensile strength. The type I fracture energy corresponding to different tensile strengths is calibrated using a direct tensile simulation test. Then, the floor heave mechanism is investigated under different lateral coefficients and tensile strengths, and five different floor heave modes are proposed under different in-situ stress lateral coefficients and tensile strengths. The floor heave modes controlled by the various in-situ stress lateral coefficients and tensile strengths are different, but they can all be explained by the maximum concentrated tangential stress. [ABSTRACT FROM AUTHOR]

Due to the variability and randomness of the geotechnical media, it is difficult to determine the constitutive parameters of the geotechnical materials in a numerical model. In this paper, a novel probabilistic back-analysis framework to update geotechnical parameters and better predict displacement due to shield excavations has been proposed. The surrogate model for the three-dimensional finite element model of shield tunneling is proposed to improve the computational efficiency based on proper orthogonal decomposition and artificial neural network (POD-ANN). In view of the cumbersome process of training the surrogate model, a training framework based on ABAQUS-PSO is presented. Considering the uncertainty factors such as the prior information of the geotechnical parameters and observation errors, probabilistic back-analysis based on Bayesian theory is implemented. The POD-ANN surrogate model and Bayesian theory are integrated to achieve an efficient back-analysis, and Delayed Rejection Adaptive Metropolis is used to solve the joint posterior distribution of the geotechnical parameters. To corroborate the effectiveness of the proposed framework, it was applied to the displacement prediction of shield tunneling under a railway project. The results show that the proposed framework can significantly improve computational efficiency and prediction accuracy. [ABSTRACT FROM AUTHOR]

A large amount of slates is distributed along Kangding No. 2 tunnel of Sichuan–Tibet Railway (China). The bedding of the Kangding slate is rich, showing apparent anisotropy of strength. For underground tunnels excavated in the anisotropic rock mass, the rock material is vulnerable to damage in tension because of its low tensile strength. Therefore, the tensile strength and fracture modes are important for the support design of layered surrounding-rock tunnel. In this study, first, a series of direct tensile tests were carried out on slate samples with five kinds of bedding dip angles. Second, the effect of bedding dip angle on the slate's tensile strength, failure modes, and acoustic emission characteristics was analyzed. Third, based on the Nova–Zaninetti criterion and the experiment results, a new phenomenological anisotropic criterion was proposed by introducing anisotropic coefficient, which could describe the nonlinear variation trend of tensile strength with foliation angles. Compared with four typical tensile strength criteria, the accuracy and universality of the new criterion were verified. Finally, the new criterion was implemented into the combined finite-discrete element method (FDEM) to conduct direct tensile simulation of slate with different foliation angles. The results indicated that the direct tensile strength followed an S-shaped increasing trend with the variation of foliation angles. The direct tensile failure modes of slate samples with different foliation angles could be divided into layer activation failure, mixed failure, and rock matrix failure. The acoustic emission process of slate with different bedding inclination under direct tension could be roughly divided into the following three stages: quiet period—stepped saltatory increase—drastic increase. The fitting effect of the new criterion was the highest among Kangding slate and other six typical layered rocks, which showed that the new criterion was suitable for predicting its Brazilian strength and direct tensile strength. At the same time, the numerical simulation results were in good agreement with the experimental results, which further verified the accuracy of the new criterion. Highlights: The acoustic emission characteristic parameters helped to reveal the direct tensile failure characteristics of layered rocks. A new phenomenological anisotropic tensile failure criterion was proposed. The direct tensile test data and the Brazilian splitting test data were used to study the accuracy and universality of the new anisotropic tensile failure criterion. FDEM was used to study the accuracy of the new anisotropic tensile failure criterion. [ABSTRACT FROM AUTHOR]

Microseismic denoising is of great significance for source localization and source parameter inversion, which lays a solid foundation for rock burst early warning. This study developed a novel hybrid complete ensemble empirical mode decomposition with adaptive noise-lifting wavelet transform (CEEMDAN-LWT)-based microseismic denoising approach. Firstly, the microseismic signal is decomposed into multiple different modes through the CEEMDAN. Then, the correlation coefficient between each mode and the microseismic signal is calculated to identify the valid, intermediate, and invalid modes. To address the issue of the coexistence of noise and useful information, the LWT is used to enhance the quality of intermediate modes. After that, the microseismic signal is reconstructed from the valid modes and the enhanced intermediate modes. In order to check the denoising capabilities of the proposed approach, a numerical experiment was carried out, and the results illustrated that the CEEMDAN-LWT achieved the highest signal-to-noise ratio (SNR) and the smallest absolute reconstruction error (ARE) in comparison with the other eight denoising methods (i.e., CEEMD-LWT, EEMD-LWT, EMD-LWT, CEEMDAN, CEEMD, EEMD, EMD, and LWT). Finally, the CEEMDAN-LWT was applied to field microseismic monitoring of a water diversion tunnel project, which further verified its effectiveness, applicability, and superiority in microseismic denoising. [ABSTRACT FROM AUTHOR]

In this paper, the coupled local fractional sine-Gordon equations are studied in the range of local fractional derivative theory. The study of exact solutions of nonlinear coupled systems is of great significance for understanding complex physical phenomena in reality. The main method used in this paper is the local fractional homotopy perturbation method, which is used to analyze the exact traveling wave solutions of generalized nonlinear systems defined on the Cantor set in the fractal domain. The fractal wave with fractal dimension ε = l n 2 / l n 3 is numerically simulated. Through numerical simulation, we find that the obtained solutions are of great significance to explain some practical physical problems. [ABSTRACT FROM AUTHOR]

Pavement roughness monitoring has been a concern in road asset management. Nevertheless, the adoption of laser profilometers for measuring pavement surface roughness poses challenges due to its high cost and inconvenience. The International Roughness Index (IRI) has been widely deployed to evaluate pavement surface roughness. Hence, there is a necessity to create a cost-efficient and simplified method for estimating IRI to assist pavement maintenance management. This study has developed a cost-effective portable roughness measurement system primarily leveraging a low-cost three-axis accelerometer and a Global Positioning System (GPS) sensor. These components are integrated with an Arduino board and installed within a vehicle to monitor road conditions effectively. Before training the model with collected data, preprocessing techniques like Kalman fusion and Fourier transform were applied to reduce errors and expand input variables. Subsequently, a Random Forest Regression (RFR) model is established to predict the IRI using optimized pavement response data. The results shows that the proposed RFR model surpasses other reference models in terms of pavement roughness estimation accuracy, exhibiting a coefficient of determination (R 2) of 0.967 and a mean square error (MSE) of 0.036. Its low cost and user-friendly nature hold promising implications for supporting decision-making in pavement maintenance within road asset management. • Develop a portable roughness measurement device based on a quarter-car model. • Integrate pavement response data with feature analysis using advanced algorithms. • Construct a machine learning model with optimized features for predicting roughness. [ABSTRACT FROM AUTHOR]

We consider a branching random walk on the real line with a stationary and ergodic environment (ξ n) indexed by time, in which a particle of generation n gives birth to a random number of particles of the next generation, which move on the real line; the joint distribution of the number of children and their displacements on the real line depends on the environment ξ n at time n. Let Z n be the counting measure at time n , which counts the number of particles of generation n situated in a Borel set of the real line. For the case where the corresponding branching process is supercritical, we establish limit theorems such as large and moderate deviation principles, central and local limit theorems on the counting measures Z n , convergence of the free energy, law of large numbers on the leftmost and rightmost positions at time n , and the convergence to infinite divisible laws. The varying environment case is also considered. [ABSTRACT FROM AUTHOR]

Many methods have been proposed to predict the field excavation performance of tunnel boring machine (TBM). They can usually predict the general trends of the field rock cutting force and efficiency when cutter penetration depth increases. However, in many cases, the predicted values are not so close (sometimes even very different) to the field values. This study is to check, compare and then correlate the prediction results of three widely used methods in predicting the field TBM excavation performance. These three methods are the laboratory LCM (linear cutting machine) method, the semi-theoretical CSM (Colorado School of Mines) method and the empirical NTNU (Norwegian University of Science and Technology) method. First, the basic procedures of these three methods are reviewed, and their prediction results are obtained concerning the TBM excavation performance in Chongqing Yangtze River Tunnel Project. Then, the quantitative comparison and correlation between the field measured result with the laboratory, semi-theoretical and empirical prediction results are conducted. After that, combined with the previous studies, some empirical formulas are proposed to predict the field TBM excavation performance at the optimum rock cutting condition more reliably and accurately. These empirical formulas can take the laboratory, semi-theoretical and empirical prediction results into comprehensive consideration. Finally, the south lot of the Qinling Tunnel in Yinhanjiwei Water Diversion Project is set as the case study, and the machine parameters and TBM excavation performance in this project are predicted and compared to the field values to verify the applicability and accuracy of the new proposed empirical formulas. Results show that the use of these new proposed empirical formulas can offer more acceptable prediction results for TBM cutterhead design and operation optimization. [ABSTRACT FROM AUTHOR]

The anisotropic behavior of layered surrounding rock has always been a hot topic in underground engineering. This paper aims to investigate the deformation characteristics and crack evolution process of layered surrounding rock under excavation unloading conditions using the three-dimensional (3D) FDEM method. Firstly, the principle of 3D FDEM method is briefly introduced, and the transversely isotropic constitutive equation is embedded in the 3D FDEM method. At the same time, by implementing the GPU parallel algorithm based on CUDA, the code is optimized to improve the computational efficiency of the 3D FDEM method. Subsequently, the Brazilian splitting specimens and uniaxial compression specimens of layered rocks are numerically simulated to study the strength and deformation anisotropy characteristics of rock specimens with different bedding dip angles. The results indicate that the tensile strength of the model gradually decreases as the bedding dip angle increases. Moreover, the compressive strength of the model exhibits a U-shaped trend with an increase in the bedding dip angle. Notably, crack propagation within the model is significantly influenced by the bedding plane. Next, the 3D FDEM method is utilized to investigate the deformation and failure characteristics of horizontally layered surrounding rock in the Jiajinshan tunnel project. It is found that there are three types of failure cracks in the surrounding rock: conjugate shear cracks, shear cracks along the bedding plane, and tensile cracks perpendicular to the bedding plane. The deformation of surrounding rock is basically consistent with the field measurement value. Furthermore, a sensitivity analysis is conducted to examine the deformation and failure characteristics of the surrounding rock under different bedding angles. This research contributes to a comprehensive understanding of the anisotropic behavior of layered surrounding rock, especially for tunnel engineering, which is of great significance in adjusting the supporting measures for the surrounding rock. [ABSTRACT FROM AUTHOR]

• An efficient Kriging-based calibration framework for FDEM is proposed. • A 3D FDEM numerical example validates the proposed method. • The proposed method employs fewer FDEM simulations to improve computational efficiency. The combined finite-discrete element method (FDEM) is a powerful numerical tool to simulate the transition of materials from continuous deformation to discontinuous fracturing and fragmentation. Calibrating parameters using laboratory data is crucial for applying FDEM to engineering-scale analysis. Considering the high computational costs in existing calibration schemes, this study proposes an effective FDEM calibration framework employing the Kriging surrogate model rooted in Uniaxial Compressive Strength (UCS) and Brazilian Tensile Strength (BTS) tests. The sensitivity analysis is first conducted on mesh size, loading rate, and numerical parameters to find a suitable set that balances computational efficiency and accuracy. Subsequently, an efficient mapping relationship between input fracture parameters and simulated strengths is established based on the Kriging surrogate model, replacing the expensive FDEM program for forward calculations. With the fracture parameters treated as unknown variables and experimental strengths available, the objective function is formulated and then solved to estimate fracture parameters. The effectiveness of the proposed method is validated through a numerical example. Compared to the conventional methods, the proposed approach requires fewer simulations of UCS and BTS, which highlights a significant computational efficiency advantage. [ABSTRACT FROM AUTHOR]

A coupled thermo-mechanical (TM) model based on the combined finite-discrete element method (FDEM) was proposed to simulate the thermal cracking of rock and granular materials. For heat conduction, it links continuous and contact heat transfer simultaneously through the continuum and discrete thermal elements, and can handle thermal contacts explicitly. For thermally induced stresses, the new TM model uses the concept of multiplicative decomposition of deformation gradient, which is consistent with the finite strain theory used in FDEM – for handling large strains and rotations. For thermal cracking, the coupling of the new TM model occurs in two directions, such as cracking in mechanical calculation affects thermal conduction, and friction caused by contact interactions generates heat, thus can capture the dynamic process of thermally induced fracturing. Four verification examples were given to validate its performance in simulating the thermal expansion in the steady-state, thermal stress in transient states, thermal cracking, and complex-shaped multibody thermal contact. The new TM model exhibits attractive features: robust to capture heat transfer for multibody thermal contact problems; better handle large strains and thermal cracking; better capture the progressive process of fracturing affects thermal conductivity; applicable to not only the steady-state but also the transient TM response. [Display omitted] • New TM model based on FDEM was proposed to model the thermal cracking of rock and granular materials. • Robust to capture multibody contact heat transfer. • Better handle large strains and thermal cracking by using multiplicative decomposition of deformation gradient. • Better capture the progressive process of thermal cracking affects heat transfer. • Applicable to not only the steady-state but also the transient TM response. [ABSTRACT FROM AUTHOR]

The degradation of rock mechanical behavior after cyclic wetting and drying could affect the stability of rock slope, embankment, and tunnel significantly. A series of tests were first conducted on sandstone collected from a reservoir bank slope. The results showed that the mechanical parameters (including tensile strength, uniaxial compressive strength, elastic modulus, and internal friction angle) decrease as the cyclic number of wetting and drying increases. Then, a damage variable, which can consider the combined influence of cyclic wetting-drying and loading, was first proposed based on test results. Further, an improved damage model, which considers the effect of cyclic wetting-drying on internal friction angle and the nonlinear deformation characteristics in the fissure closure stage, was established with statistical damage mechanics. The determination method for the parameters in the proposed damage model was also introduced. Finally, the effectiveness of proposed model was verified by comparing with experimental data. The verification indicates that the results from the improved model agree well with test results, and the improved model can enhance the prediction accuracy over the original model. [ABSTRACT FROM AUTHOR]

The study of coal oxidation and weight gain at low temperatures is helpful in understanding the spontaneous combustion of coal and its mechanisms. In this study, we comprehensively investigated the low-temperature oxidation properties and the oxygen adsorption weight gain kinetics of Chinese Shenhua subbituminous coal (SH). Using thermogravimetric experiments with various particle sizes, heating rates, and coal ranks, the oxygen adsorption mass gain stages of coal oxidation at low temperatures were investigated. According to the results of these experiments, as the particle size of SH coal decreased, the dry cracking temperature (T1) decreased, the ignition temperature (T2) changed slightly, the weight gain increased, and the spontaneous combustion tendency increased. The three-dimensional diffusion model (Zhuralev-Lesokin-Tempelman) (D5) is suitable for SH coal samples with different particle sizes. A higher heating rate is not conducive to the formation of carbon-oxygen complexes. The D5 model can also be used to fit the kinetics of the SH coal samples at 5 K/min, 10 K/min, and 30 K/min. Unlike the SH coal samples, the Shengli lignite (SL) and Tavan Tolgoi anthracite (TT) samples fit the three-dimensional diffusion model (Jander) (D3). Based on the fitting results of the Achar differential method and the Coats-Redfern integral method, the activation energy E of the low-temperature oxidation weight gain of the coal samples decreases with decreasing coal particle size and with increasing oxidation rate and coal rank. [ABSTRACT FROM AUTHOR]

The design of rock engineering projects requires an estimation of the strength of intact rock blocks. These blocks can be significantly larger than the typical laboratory test specimen; thus, understanding the specimen size effect on mechanical properties is essential. In this paper, a series of uniaxial compression tests and Brazilian disc tests were conducted on cylindrical samples with diameters varying from 20 to 150 mm, and direct shear tests were conducted on cubic samples with side lengths varying from 50 to 200 mm. The results showed that the uniaxial compressive strength (UCS), cohesion, and Young's modulus decrease with increasing specimen size, whereas the tensile strength initially increases and then decreases. Moreover, the applicability of different size effect models to experimental data was assessed. It was concluded that the fitting equations of UCS and cohesion are almost the same, whereas that of tensile strength is significantly different. The size effect law of rock mechanics parameters may be affected by the failure mode. [ABSTRACT FROM AUTHOR]

To address the problem of cyan-green light deficiency in fluorescent converters for laser diode (LD) illumination applications, Ca 3-x Sc 2 Si 3 O 12 :xCe3+ (CSS:xCe3+) cyan-green fluorescent ceramics and CSS:Ce3+ phosphor in glass (CSS:Ce3+-PiG) fluorescent converter were successfully prepared. Among them, the CSS:0.08Ce3+ cyan-green fluorescent ceramic and 20 wt% CSS:Ce3+-PiG fluorescent converter had the highest luminescence intensity. At 450 nm excitation, the emission spectra of both materials showed an asymmetric broadband band between 470 nm and 690 nm. And the two fluorescent converters are not appear of luminescence temperature quenching until more than 538 K. The performance of the white LDs synthesized with ceramic and PiG converters was investigated. Under different power excitation, the green emission intensity of both wLD is enhanced with increased incident laser power. The wLDs based on CSS:Ce3+ fluorescent ceramics have a luminous flux of 880 l m and the maximum luminescence efficiency of 176 l m/W at an incident power of 5 W. And the wLDs of PiG fluorescent converters have a maximum luminous flux of 584 l m and luminescence efficiencies of up to 117 l m/W. CSS:Ce3+ ceramics and CSS:Ce3+-PiG are green fluorescent converter with good luminescence performance and thermal stability. It will play an important role in the compensation of the cyan light in LD illumination. [ABSTRACT FROM AUTHOR]

Grouting reinforcement technology is a vital component of geotechnical engineering, which plays a crucial role in repairing surrounding rock that is damaged and improving its strength. To analyze the impact of grouting on the mechanical properties of rock fractures, specimens of mudstone fractures were selected before and after grouting reinforcement for direct shear tests. The purpose was to investigate the changes in mechanical properties under normal and tangential loading conditions. Furthermore, the microscopic–mesoscopic and macroscopic aspects of grouting reinforcement were discussed to explore its influence on the interface structure, deformation resistance, and strength of the fractured rock mass. By analyzing the test results of the fracture's mechanical properties before and after grouting, a constitutive model and strength criterion were proposed to accurately describe the mechanical behavior of the fracture surface. Building on a numerical software platform, the custom model was compiled with the VC++ integral programming environment and embedded in UDEC software. Finally, these findings were successfully applied to a typical deep roadway surrounding rock grouting reinforcement project, which showcased the practical implications of this paper. The results demonstrate that grouting reinforcement significantly impacts the normal and tangential mechanical properties of the fracture surface and the shrinkage and dilatation mechanical behaviors. The grout filling and cementation process enhances the rock mass fracture's resistance to deformation, effectively preventing the gradual weakening and slip in the fracture field. This improves the overall integrity and stability of the rock mass. The proposed mechanical model effectively captures the compression, shear, shrinkage, and dilatation mechanical behaviors before and after grouting. Similarly, the custom fracture grouting mechanical model could be a useful tool to simulate the behavior of grouting reinforcement in engineering rock masses. [ABSTRACT FROM AUTHOR]

Pressure arch utilises the self-stabilizing capacity of surrounding rock and is benefit to the roof stability of underground excavations. The analysis of it provides a new stability assessment tool for underground engineering. In this paper, a series of numerical simulations were carried out to investigate the formation and properties of pressure arch and the self-stabilisation mechanism of surrounding rock. It is found that stress redistribution results in the formation of the pressure arch. The inner and outer boundary of arching area are determined as the principal stress trajectories through the inflection points of the principle stress-depth curves on the centre line of caverns. Furthermore, parametric analysis illustrates that in situ stress ratio and excavation size have more significant effect on the inner and outer boundaries and the arch thickness than roof shape and overburden depth. Finally, it can be observed that the various trends of the inner boundary height with different influence factors are same with the displacement of the crown, and it could be used as an indicator for stability assessment. Based on the observed phenomena, a design scheme is proposed to determine the maximum size of the underground openings cross-section without support in agreement with the geomechanical conditions. [ABSTRACT FROM AUTHOR]

• A novel thermo-mechanical coupling scheme is developed based on the combined finite-discrete element method (FDEM) to capture the mechanical response of the rock to the isotropic/anisotropic thermal conduction process. • The mechanisms of the creation and development of the excavation damaged zone (EDZ) around the wellbore subject to excavation unloading, drilling mud support, and thermal change in the surrounding rock are analyzed. • The influences of the thermal-mechanical properties of the rock mass, such as the isotropic/anisotropic rock strength and thermal conductivity, thermal expansivity, as well as drilling mud-rock thermal interaction process, on the EDZ development, are discussed. Insights into fracture development and excavation damaged zone (EDZ) formation around wellbore excavation sites are essential for understanding wellbore stability. In this study, a novel thermo-mechanical scheme is implemented in the 2D combined finite-discrete element method (FDEM) to investigate the fracturing process around a wellbore in a high-temperature subsurface environment. The developed scheme captures the isotropic/anisotropic thermal conduction characteristics within the rock formation. The coupled scheme and stress distributions around the wellbore subject to in-situ stress, drilling mud pressure, and temperature changes are validated by closed-form solutions. Fracture development and progressive EDZ formation by various mechanisms are analyzed. The results show that for an unsupported wellbore, fractures initiate in the region of the most severe stress concentration due to excavation unloading and constitute an EDZ that resembles the logarithmic-spiral rupture zone captured by experimental observations and Mohr-Coulomb models, resulting in potential water inrush due to the significantly increased fracture transmissivity of the EDZ and wellbore collapse. The shape and extent of the EDZ for wellbore excavation in the layered rock mass are dominated by the stress redistribution and the presence of low-strength bedding planes favorably oriented for bedding slippage. The excavation unloading-induced stresses can be effectively counteracted by properly applying drilling mud pressure, and the disturbance of the stress field occurs only within a small region, greatly reducing the extension of the EDZ. Thermal contraction of the surrounding rock due to its convective interaction with the cold drilling mud induces extra fractures around the wellbore. The extension of the EDZ is greater with increased thermal expansivity of the rock formation. Overall, the results indicate that the adopted thermo-mechanical FDEM simulation can provide unique geomechanical insight into wellbore stability behavior analysis, in which explicit consideration of the fracturing and fragmentation processes is of great significance. [ABSTRACT FROM AUTHOR]

In this study, quadratic element formulations (i.e., ten-node tetrahedral elements and twelve-node cohesive elements) are proposed to improve the computational accuracy of the three-dimensional combined finite-discrete element method (3D FDEM). The ten-node tetrahedral element formulation is developed based on the isoparametric transformation. As for the twelve-node cohesive element formulation, the opening displacement is described by quadratic interpolation within the element, which is fully compatible and connected with the adjacent ten-node tetrahedral elements. To integrate quadratic element formulations into FDEM, a novel and more generalized updated Lagrangian framework (UL-FDEM) is developed to replace the non-Cartesian framework in the original FDEM. The equilibrium equation of UL-FDEM is established based on the principle of virtual work. Subsequently, the governing equation of UL-FDEM is derived by employing the isoparametric discretization techniques. Several numerical examples are provided to illustrate the effectiveness of the proposed approach. The results demonstrate that this approach is well-suited for the geometrically nonlinear analysis and achieves higher accuracy in stress and fracturing predictions than the original FDEM under the same mesh size. The proposed approach can use fewer elements to perform fracturing analysis, thus improving computational efficiency. [ABSTRACT FROM AUTHOR]

With the rapid development of deep underground engineering, grouting technology is widely used to enhance the stability of the surrounding rocks in tunnels, where ingress water, large site disturbance, and deformation are the main challenges. In this paper, a three-dimensional (3D) numerical grouting system, which is based on TOUGH2 and the finite element method (FEM), is developed to study the diffusion and consolidation of grout slurry during the cyclic grouting process. It is observed that the grouting technology can reduce the rock permeability and porosity, increase the degree of compactness, and improve the strength of the rock mass. This numerical grouting system is validated by three numerical tests. The grout diffusion and consolidation process are investigated by simulating grouting experiments. Finally, a detailed mining tunnel grouting schedule is designed, and the corresponding numerical model is established to mimic stopping the water ingress. The results show that the grouting system presented in this study is potentially useful to improve the grout characteristics and tunnel designs, as well as construction. [ABSTRACT FROM AUTHOR]

The excavation in layered rocks is an issue for a number of geoengineering applications; these kinds of rocks all exhibit transverse isotropic features due to the process of metamorphic differentiation. This paper focuses on providing two methods, i.e., the 3D printing technology and the combined finite-discrete element method, to simulate the anisotropic characteristics of layered rocks. The results showed that both the 3D-printed samples and the FDEM numerical models are considered as a good match, and both revealed that as the inclined angle increased, the UCS of the sample first decreased and then increased, showing a U-shaped pattern. The results of this paper served as a reference to the promotion of the 3D printing technology and the combined finite-discrete element method in the geotechnical engineering field and laboratory test research. [ABSTRACT FROM AUTHOR]

The dynamic behavior of the tumor suppressor p53 as an important signal in response to various stresses can influence cellular fate decisions. Programmed cell death 5 (PDCD5) and wild type p53-induced phosphatase 1 (Wip1) regulate p53 dynamics as its activator and inhibitor, respectively. In the present study, we add Wip1 to p53-Mdm2 (Murine double minute 2) module with PDCD5 and focus on p53 dynamics depending on PDCD5 and ataxia telangiectasia mutated (ATM) degradation rate regulated by Wip1. The bifurcation results reveal that p53 dynamics varies with these two parameters. p53 exhibits monostability and bistabiltiy for smaller and larger PDCD5 level while p53 shows oscillation or coexistence of oscillation and steady states in a narrow parameter range. These dynamics are further explored by time series and potential landscapes. Our results may be useful for regulating cell fate upon DNA damage. [ABSTRACT FROM AUTHOR]

Let (N , A 1 , A 2 , ...) be a sequence of random variables with N ∈ N ∪ { ∞ } and A i ∈ R + . We are interested in asymptotic properties of non-negative solutions of the distributional equation Z = (d) ∑ i = 1 N A i Z i , where Z i are non-negative random variables independent of each other and independent of (N , A 1 , A 2 , ...) , each having the same distribution as Z which is unknown. For a solution Z with finite mean, we prove that for a given α > 1 , P (Z > x) is a function regularly varying at ∞ of index − α if and only if the same is true for P (Y 1 > x) , where Y 1 = ∑ i = 1 N A i . The result completes the sufficient condition obtained by Iksanov & Polotskiy (2006) on the branching random walk. A similar result on sufficient condition is also established for the case where α = 1. [ABSTRACT FROM AUTHOR]

This study is to investigate the change in resultant force, cutting coefficient and normalized resultant force of the TBM (tunnel boring machine) disc cutter when using different cutting conditions and different linear cutting machines. Full-scale linear cutting tests on three rocks of different compressive strengths were conducted. The experimental results, combined with other previously published data, were compared to the prediction results of the semi-theoretical CSM (Colorado School of Mines) prediction model. The influences of rock compressive strength, disc cutter diameter and machine frame stiffness on the comparison results were analysed. From the general view, experimental resultant forces tend to be underestimated while experimental cutting coefficients and normalized resultant forces both tend to be overestimated when using the semi-theoretical CSM prediction model, and the underestimation or overestimation degrees are different when the above three influencing factors are different. The reason responsible for these phenomena can be mainly attributed to the lower actual cutter penetration depth compared to the pre-set one during the rock–machine interaction process. The results of this study can offer more accurate understanding of the full-scale linear cutting tests using different cutting conditions and different linear cutting machines, and thus it can contribute to the more reliable and accurate prediction on disc cutter cutting forces. [ABSTRACT FROM AUTHOR]

To study the toughening effect and the anchoring mechanism of rock bolts, fractured rock specimens with different crack angles and different crack lengths are made of cement mortar. The prefabricated specimens are applied with different anchoring modes for reinforcement, containing no-anchoring, full-length bonded anchoring and pre-stressed anchoring. The uniaxial compression tests of fractured rock specimens under different anchoring modes are carried out, and then the mechanical properties and the failure modes of fractured rock specimens before and after anchoring are analysed. The 'Cavity Damage Effect' is defined and the test results show that the peak strength of the fractured specimens are roughly proportional to the crack inclination angle due to the 'Cavity Damage Effect', the crack is equivalent to a 'cavity damage' inside the prefabricated specimen if the opening of the crack is larger. The crack length can significantly affect the strength and deformation characteristics of no-anchoring specimens, while has little influence on the anchoring specimens. The full-length bonded anchoring and the pre-stressed anchoring can both significantly increase the mechanical parameters (the peak strength, residual strength and elastic modulus) of the specimens, enhance the resistance to deformation of fractured rock mass, and inhibit the expansion and coalescence of cracks. [ABSTRACT FROM AUTHOR]

• An analytical viscoelastic model is established to solve stress based on RSR method. • The explicit stress on interfaces of rock-grout and grout-transducer was obtained. • The stress first increases and then keeps constant as diameter ratio increases. • The rheological time increases as viscosity coefficient and the modulus ratio increase. The rheological stress recovery (RSR) method was proposed to measure the in-situ stress of rock mass with time-dependent property by drilling a hole and embedding transducers into it. To solve the stress distribution on the transducer, a viscoelastic axisymmetric plane model was firstly built considering an arbitrary stress boundary condition. The analytical solution was developed by dividing the stress boundary conditions into axisymmetric and anti-axisymmetric combining with Laplace transformation technique. The explicit stress expressions on interfaces of rock–grout and grout–transducer was obtained using Burgers and Boltzmann viscoelastic models, respectively. Furthermore, the variations of transducer surface final stress, which is related to rheological time, geometric and mechanical properties of rock mass, grout parameter, and transducer materials, was proposed for calculating the measured stress by RSR method. For both of Burgers and Boltzmann viscoelastic model, final stress increases as elastic modulus ratio increases when elastic modulus ratio under 20, and the final stress could be ignored when diameter ratio is over 1.4. The rheological time increases with increasing of viscosity coefficient and the modulus ratio, but decreases as the shear modulus increases. The results in here provide a simple method for stress analyzing and have great value for understanding the relationship between the initial stress of rock mass and the measured stress for the RSR method. [ABSTRACT FROM AUTHOR]

Calcium has been proved to be efficient for the catalytic steam gasification of lignite. In this study, we studied the steam gasification of lignite with Ca(OH) 2 added by wet impregnation for to produce hydrogen. The effect of calcium on the microstructural evolution and char gasification behavior in the presence of steam were studied. The distribution of the gaseous products was examined by using fixed-bed micro reactor equipment for steam gasification. Partially gasified chars obtained at different temperatures (400, 500, 600, and 700 °C) in the gasification process were characterized by scanning electron microscopy coupled with energy dispersive spectroscopy, 13C nuclear magnetic resonance, Fourier-transform infrared spectroscopy, and Raman spectroscopy. The results suggested that a "Ca-carboxylate-like structure" was formed due to the addition of calcium to lignite. This Ca-carboxylate-like structure increased the thermal stability of the original carboxylic structure in lignite. As a result, the calcium-added coal retained more oxygen-containing structures, formed more defects, and possessed significantly lower aromatic structures due to the formed Ca-complexes during steam gasification. Therefore, it can be inferred that the Ca-complexes in the lignite char increased the gasification reactivity of char. • Reduced gasification temperature, enhanced reactivity and H 2 by adding calcium. • Strongly changes of char texture under reaction state by added calcium. • Indispensable effect of Ca-carboxylate evolution on the structure of lignite char. • Dependence of gasification characteristics on structural evolution. • Catalytic mechanism of gasification process on structural evolution. [ABSTRACT FROM AUTHOR]

Summary: This paper focuses on the efficiency of finite discrete element method (FDEM) algorithmic procedures in massive computers and analyzes the time‐consuming part of contact detection and interaction computations in the numerical solution. A detailed operable GPU parallel procedure was designed for the element node force calculation, contact detection, and contact interaction with thread allocation and data access based on the CUDA computing. The emphasis is on the parallel optimization of time‐consuming contact detection based on load balance and GPU architecture. A CUDA FDEM parallel program was developed with the overall speedup ratio over 53 times after the fracture from the efficiency and fidelity performance test of models of in situ stress, UCS, and BD simulations in Intel i7‐7700K CPU and the NVIDIA TITAN Z GPU. The CUDA FDEM parallel computing improves the computational efficiency significantly compared with the CPU‐based ones with the same reliability, providing conditions for achieving larger‐scale simulations of fracture. [ABSTRACT FROM AUTHOR]

Determination of the TBM disc cutter performance at the optimum rock cutting condition is very important, but the existing theoretical, laboratory, numerical or empirical methods still have some shortcomings. Full-scale rock cutting test is regarded as the most accurate and reliable method in the laboratory, but it still requires large rock blocks and specific testing equipment, which make the use of this method very limited and costly. Thus, by collecting, analyzing and formulizing the results of many full-scale linear cutting tests, this study partly overcomes the shortcoming of the full-scale rock cutting test and proposes some new empirical formulas to predict TBM disc cutter performance in a much easier and less costly way. First, this study reveals the general rules to characterize the change of rock cutting results with the increase of rock uniaxial compressive strength and cutter penetration depth by conducting full-scale linear cutting tests on five different rock types. Then, by analyzing a large amount of full-scale linear cutting test results, this study correlates the TBM disc cutter performance at the optimum rock cutting condition with rock uniaxial compressive strength and a widely used semi-theoretical prediction model. The new proposed empirical formulas in this study only use rock properties, cutter geometries and cutting geometries to design the machine specifications and select the TBM operation parameters, which is a much easier and less costly method. [ABSTRACT FROM AUTHOR]

In this work, the propagation of higher-dimensional nonlinear Rossby waves under the generalized beta effect is considered. Using the methods of weak nonlinear perturbation expansions and the multiple scales, we obtain a new (2 + 1)-dimensional generalized Boussinesq equation from the barotropic potential vorticity equation for the first time. Furthermore, a new dispersion relation for the linear Rossby waves is given corresponding to the linearized Boussinesq equation. More importantly, based on the methods of the traveling wave setting and the Jacobi elliptic function expansions, several kinds of exact traveling wave solutions for the higher-dimensional nonlinear Rossby waves, including the periodic solutions, solitary solutions and others are obtained. Finally, we simulate the solitary solutions obtained by using the method of the Jacobi elliptic function. The numerical results show that the amplitude of the Rossby solitary waves is decreasing with the increase of generalized beta effect. [ABSTRACT FROM AUTHOR]

Identifying the surrounding rock loads acting on the external shield surface is critical to the safe construction of deep and long tunnels excavated by TBMs (tunnel boring machines). However, it is rather difficult or even impossible to carry out monitoring outside the TBM shield to directly determine the surrounding rock loads. In the present paper, based on modified Newton iteration and numerical simulation, an inverse analysis approach to identify the surrounding rock loads is proposed. This inverse problem is solved by minimizing the objective function that incorporates the difference between the monitored and calculated strains of discrete points on the internal TBM shield surface. During the inverse analysis, the external TBM shield surface is discretized into rectangular regions, and the nodal loads of each region are taken as the inverse parameters. Then, the distributed loads are approximately calculated by the interpolation of the nodal loads of each region. The proposed approach is calibrated with two numerical examples and then applied to analyze in situ monitoring data. The results show that the proposed approach is robust and efficient for identifying the distribution and magnitude of surrounding rock loads, and it is possible to carry out timely countermeasures to avoid shield jamming according to the identified loads. [ABSTRACT FROM AUTHOR]

Taking the tunnel face effect and time-dependent properties of soft surrounding rock into consideration, the spatial and temporal effects of squeezing deformation in the shield region are studied, and their determining influences on the interaction of contact-squeezing-friction between surrounding rock and shield is analysed. Then the mechanism of TBM shield jamming is revealed as follows: firstly, the radial convergence in the shield area increases with the increasing distance to the tunnel face and the growing stoppage downtime gradually; secondly, the convergence may exceed the overcut gap at a certain distance from the face where the surrounding rock starts to contact and squeeze the shield; as a result, frictional resistance is produced between the surrounding rock and shield; if the thrust supplied by the TBM propulsion system is insufficient to overcome the frictional forces when TBM advances forward, then the shield of TBM will become entrapped. Subsequently, based on the Convergence–Confinement method and the previously established constitutive model for squeezing soft rock, the calculation methods for the interaction curves (Longitudinal Deformation Profile, Ground Response Curve and Support Characteristic Curve) between soft ground and shield are put forward. Then the forecasting model for shield jamming inoculation process, the trigger condition and criterion for shield jamming are established. These forecasting models are illustrated and verified by a case study finally. [ABSTRACT FROM AUTHOR]

In this study, determination of some machine parameters and performance prediction for tunnel boring machine (TBM) are conducted based on laboratory rock cutting test. Firstly, laboratory full-scale linear cutting test is carried out using 432-mm CCS (constant cross section) disc cutter in Chongqing Sandstone. Then, the input parameters for TBM cutterhead design are extracted; some TBM specifications are determined and then compared to the manufactured values. Finally, laboratory full-scale linear cutting test results are compared with the field TBM excavation performance data collected in Chongqing Yangtze River Tunnel. Results show that laboratory full-scale linear cutting test results, combined with some engineering considerations, can be used for the preliminary and rough design of TBM machine capacity. Meanwhile, combined with some modification factors, it can also well predict the field TBM excavation performance. [ABSTRACT FROM AUTHOR]

Deep reinforcement learning (DRL) is gaining attention as a machine learning tool for effective active control strategy development. This study focuses on employing DRL to develop an efficient active control strategy for flow around three circular cylinders arranged in an equilateral-triangular configuration in a two-dimensional channel. The analysis of control outcomes reveals that DRL induces vortices of varying sizes between the cylinders, resulting in large elliptical vortices at the rear. This enhancement in flow stability leads to a significant 40.40% reduction in cylinder drag force and an approximate 8.23% decrease in overall drag oscillations. Our research represents a pioneering application of DRL for stabilizing complex flow around multiple cylinders, yielding remarkable control effectiveness. The noteworthy outcomes in controlling the stability of complex flows highlight the capability of DRL to grasp intricate nonlinear flow dynamics, showcasing its potential for investigating active control strategies within complex nonlinear systems. [Display omitted] • Demonstrating deep reinforcement learning in non-linear, complex flow problems. • Remarkable 40.40% drag reduction, 8.23% less overall drag fluctuations. • Efficient implementation of real-time, multi-point active control for complex flow. [ABSTRACT FROM AUTHOR]

Rockbursts have become one of the main engineering disasters in deep-buried tunnel, seriously threatening the safety of worker and equipment. To monitor microseismic (MS) events and predict rockburst, in the present study, a MS monitoring system was established in a deep-buried tunnel excavated by tunnel boring machine (TBM). Characteristics of MS events were studied and a prediction method for intense rockburst was proposed by analyzing the temporal–spatial distribution, source parameters, and failure mechanism. The results indicated that most of MS events occurred during the tunneling process and within 15 min after a tunneling cycle completed. The MS events mainly distributed within 15 m before and after the tunneling face, and within approximate 2.0 times of the tunnel diameter. The energy of these MS events mainly ranged from 30 to 100 kJ. The prediction method based on cumulative energy index of per day and cumulative apparent volume cannot predict intense rockburst accurately in the present study, the forecast accuracy less than 60%. The proposed prediction index based on the energy index of per MS event and the apparent volume of per MS event can effectively sharpen the forecast accuracy (> 85%). The failure mechanism of MS events was predominated by tensile failure. While as the rockburst segment transited from mild to intense, the percentage of MS events of mixed failure and shear failure increased, especially shear failure events. Highlights: The temporal and the spatial distribution characteristics of rockburst segment in a deep-buried tunnel were revealed. Microseismic event count, energy, energy index, apparent volume, failure mechanism, and the development process of mild, moderate, and intense rockburst segments were studied. A prediction index based on energy index and apparent volume of per microseismic event was proposed to forecast intense rockburst. [ABSTRACT FROM AUTHOR]

White light solid-state lighting applications still face significant challenges due to insufficient efficient and stable red light emitting materials. Therefore, a series of orange-red fluorescent materials, CaLu 2-x Mg 2 Si 3 O 12 :xCe3+ (CLMS:xCe3+; x = 0.02, 0.04, 0.06, 0.08, 0.10, 0.12) were prepared in this paper. Luminescence spectra testing revealed that the optimal concentration of Ce3+ ions in the crystal lattice is x = 0.04. At 460 nm excitation, the emission wavelength is approximately 592 nm. To enhance the thermal stability and luminescence performance of CLMS:Ce3+, the CaLu 1.96-y Me y Mg 2 Si 3 O 12 :0.04Ce3+ (Me = Sr, Ba; y = 0, 0.02, 0.05, 0.10, 0.15, 0.20) fluorescent materials were successfully prepared. It was found that phosphor's fluorescence intensity was enhanced after the introduction of Sr2+ or Ba2+ ions. Meanwhile, the phosphors were tested for thermal stability, and the emission intensities of CLMS:0.04Ce3+, CLMS:0.04Ce3+,0.10Sr2+, and CLMS:0.04Ce3+,0.05Ba2+ phosphors decreased to 77.60%, 85.53%, and 87.63% at 423 K, respectively. This proves that Sr2+ and Ba2+ ions have a positive effect on the thermal stability performance of CLMS:0.04Ce3+ phosphor. Testing of the w-LED devices, the CCT was reduced. The CRI was improved to 80.4 and 81.6 and luminescence efficiency was improved to 107.71 lm/W and 115.04 lm/W after Sr2+ or Ba2+ ions were introduced. In summary, this study demonstrates that CaLu 2-x-y Me y Mg 2 Si 3 O 12 :xCe3+ (Me = Sr, Ba) is an auspicious fluorescent material with high thermal stability, which is potentially informative for the field of white-light illumination. [ABSTRACT FROM AUTHOR]

White light solid-state lighting applications still face significant challenges due to insufficient efficient and stable red light emitting materials. Therefore, a series of orange-red fluorescent materials, CaLu 2-x Mg 2 Si 3 O 12 :xCe3+ (CLMS:xCe3+; x = 0.02, 0.04, 0.06, 0.08, 0.10, 0.12) were prepared in this paper. Luminescence spectra testing revealed that the optimal concentration of Ce3+ ions in the crystal lattice is x = 0.04. At 460 nm excitation, the emission wavelength is approximately 592 nm. To enhance the thermal stability and luminescence performance of CLMS:Ce3+, the CaLu 1.96-y Me y Mg 2 Si 3 O 12 :0.04Ce3+ (Me = Sr, Ba; y = 0, 0.02, 0.05, 0.10, 0.15, 0.20) fluorescent materials were successfully prepared. It was found that phosphor's fluorescence intensity was enhanced after the introduction of Sr2+ or Ba2+ ions. Meanwhile, the phosphors were tested for thermal stability, and the emission intensities of CLMS:0.04Ce3+, CLMS:0.04Ce3+,0.10Sr2+, and CLMS:0.04Ce3+,0.05Ba2+ phosphors decreased to 77.60%, 85.53%, and 87.63% at 423 K, respectively. This proves that Sr2+ and Ba2+ ions have a positive effect on the thermal stability performance of CLMS:0.04Ce3+ phosphor. Testing of the w-LED devices, the CCT was reduced. The CRI was improved to 80.4 and 81.6 and luminescence efficiency was improved to 107.71 lm/W and 115.04 lm/W after Sr2+ or Ba2+ ions were introduced. In summary, this study demonstrates that CaLu 2-x-y Me y Mg 2 Si 3 O 12 :xCe3+ (Me = Sr, Ba) is an auspicious fluorescent material with high thermal stability, which is potentially informative for the field of white-light illumination. [ABSTRACT FROM AUTHOR]

The large deformation mechanisms and predictions of soft rock tunnels have always been important but difficult to solve problems in the field of geotechnical engineering. A combined finite–discrete element numerical simulation method (FDEM) was used to study large deformation mechanism, classification and prediction. The deformations or failure mechanisms of tunnel surrounding rock were revealed, and the failure modes and displacement value prediction of surrounding rock with different strength-stress ratios were also investigated. The following conclusions were obtained: (1) Critical hysteresis damping can be adopted to simulate the progressive large deformation process of soft rock tunnels, which can obtain the final deformation of unsupported tunnels and avoid a dynamic response. (2) Under concentrated tangential stress, the surrounding rock undergoes X-shaped conjugate shear fracture, and this type of fracture network continues to propagate toward the depth of the surrounding rock until the model reaches a stable state; the reduction in tunnel cross-section is mainly caused by the macroscopic movement and volume expansion of rock fragments, and the latter is due to the generation of a large number of macroscopic voids. (3) As the strength-stress ratio decreases, the deformation or failure modes of the surrounding rock can be divided into four categories: elastic–plastic deformation, closed fracturing, shear dilation and broken expansion. (4) Finally, a prediction equation for isotropic and homogeneous soft rock unsupported tunnel deformation with general size driven by hydrostatic in situ stress is obtained, which indicates that with an increasing strength-stress ratio, the surrounding rock displacement decreases as an exponential function, with a correlation coefficient of R 2 = 0.997. In addition, the robustness and reliability of the prediction equation is verified. [ABSTRACT FROM AUTHOR]

• A new phenomenological tensile failure criterion with an anisotropic coefficient was proposed. • Direct tensile test of the Kangding slate was carried out to verify the accuracy of the new criterion. • The tensile strength data of eight typical layered rocks were collected and compared with the other six typical tensile strength criteria to verify the universality and superiority of the new criterion. • Based on the sensitivity analysis of tensile rate, the loading rate of 0.01 m/s was recommended for the samples with various foliation angles. • Layer thickness has little effect on tensile strength, but a significant effect on tensile failure modes. The tensile strength is a key parameter for the design of many geotechnical engineerings such as tunnel support, slope support, and petroleum drilling. The tensile strength in layered rocks, however, is anisotropic due to the existence of bedding planes. In this paper, to study the anisotropic tensile behaviors, a series of direct tensile tests were conducted using Kangding slate with five different foliation angles (β = 0°, 30°, 45°, 60°, and 90°). Based on the N-Z criterion, a new tensile failure criterion with the anisotropic coefficient was proposed. The tensile strength data of nine typical layered rocks were collected to evaluate the prediction ability of seven anisotropic tensile failure criteria including the new criterion. Embedding the new criterion into FDEM, the loading rate-dependent and layer thickness-dependent tensile mechanism of layered rock under direct tensile test were simulated. The experimental and numerical simulation results showed that the foliation angle significantly affected the tensile strength and failure modes of the slate. With the increase of foliation angle (β), the tensile strength of nine typical layered rocks, including Kangding slate, presented a non-linear increase trend. Compared with the other six typical anisotropic tensile failure criteria, the new criterion has the best prediction capability on the tensile strength of rocks with four different anisotropic degrees, and therefore the new criterion was recommended. The new criterion was embedded in FDEM to carry out direct tensile simulation of slate with different β. The numerical simulation results were in good agreement with the experimental results, further verifying the accuracy of the new criterion. The loading rate sensitivity analysis indicated that a tensile rate of 0.01 m/s was recommended to assure quasi-static loading of the specimen. Through the sensitivity analysis of layer thickness, it is concluded that layer thickness has very little influence on tensile strength, but has a very significant influence on the final failure modes of the specimens. [ABSTRACT FROM AUTHOR]

The combined finite-discrete element method (FDEM) is an advanced finite element and discrete element coupling method, which is commendably suitable for simulating the slope's entire evolution process from cracking, expansion, penetration, sliding, collision to deposition under seismic load. The original FDEM has apparent shortcomings in simulating the dynamic instability process of earthquake-induced landslides, and some targeted improvements are made to the original program. Numerical tests are carried out to prove the accuracy and robustness of the improved FDEM, and the influence of the structural plane on the dynamic evolution mechanism and process of the slope is studied. The results show that the improved FDEM can accurately reproduce the entire dynamic evolution processes and failure forms of different jointed rock slopes under seismic load and can quantitatively evaluate the dynamic stability of jointed rock slopes (dynamic safety factor and critical failure surface). In addition, the results also emphasize that the slope failure degree significantly affects the dynamic response of the slope and suggest that the combination of the cut-through of the failure surface and the increase of kinetic energy should be used as the criteria for slope dynamic instability simulation by FDEM. This study provides scientific and technological support for revealing the failure mechanism of jointed rock slopes and disaster reduction and prevention. [ABSTRACT FROM AUTHOR]

In this paper, we discuss a fifth-order b -family peakon model with cubic nonlinearity, called the fifth-order b -family Novikov (FObFN) model. Interesting solutions are provided including explicit single pseudo-peakons, two-peakons, and N -peakon solutions. In particular, detailed dynamical interactions of two-peakons and three-peakons are investigated numerically. [ABSTRACT FROM AUTHOR]

Accurate simulation of the propagation of hydraulic fractures under in situ stress conditions in three dimensions (3D) is critical for the enhanced design and optimization of hydraulic fracturing in various engineering applications, such as shale gas/oil production and geothermal utilization. To model fracture propagation for geotechnical applications numerically, a maximum principal stress criterion (MPS-criterion) with a weighted average approximation is conventionally applied. However, it is found that the weighted average approximation is inappropriate for hydraulic fracturing under in situ stress conditions, where the presence of both hydraulic pressure and in situ stress can lead to sharp changes of the stress field in the vicinity of the fracture tips. When both hydraulic pressure and in situ stress are considered, the simulated results with the weighted average approximation are inaccurate and are sensitive to the radius of the computational area. In this paper, we present numerical tests to identify this limitation of the weighted average approximation and propose a novel point-based approximation for the MPS-criterion. The performance of the MPS-criterion with the point-based approximation for hydraulic fracturing under in situ stress conditions is confirmed by a numerical test. It can be seen that, compared to the traditional weighted average approximation, the MPS-criterion with the point-based approximation is more stable and accurate for modelling hydraulic fracturing under in situ stress conditions. [ABSTRACT FROM AUTHOR]

• The maximum mesh size and maximum loading rate that can be adopted for different specimens are proposed. • The maximum mesh size and calculation method for tunnel excavation simulation of different diameters are proposed. • The method for determining the critical kinetic energy of the system during excavation simulation is proposed. • The reduction function of the Young's modulus of the core material is proposed. The combined finite-discrete element method (FDEM) is extensively employed to model rocks and rock-like materials, in which calibration against the results from uniaxial/triaxial compression tests, Brazilian tests and shear tests have been widely carried out. However, since different element sizes and loading rates were used, it is difficult to assess the numerical results of these studies if the effects of the element size and loading rate are ignored. This paper discusses the effect of the element size, loading/unloading rate and unloading mode on the cracking processes in laboratory-scale (uniaxial compression tests and Brazilian tests) and field-scale (circle tunnel excavations). The results indicate that the element size and loading rate should not be less than 27–28 meshes in a diameter zone and larger than 0.5 m/s, respectively, in laboratory-scale. In field-scale models, four different tunnel diameters (3, 4, 5 and 6 m) are used in tunnel excavation simulations. The results reveal that the mesh number around the tunnel wall should not be less than 120, meanwhile the element size should not be longer than the length of fracture process zone (l FPZ). The unloading rate for the field-scale model is influenced by the model size and rock density. It cannot be determined directly but a new method is proposed to determine the unloading rate based on crack development curve. To compare the fracture patterns well to those observed from the tunnel simulations, the unloading mode of an exponential formula is apposite. [ABSTRACT FROM AUTHOR]

Since rock mass in many fields of rock engineering usually undergoes a cyclic heating and cooling process, it is very meaningful to investigate the variations of rock micro/macro physical and mechanical properties subjected to cyclic heating and cooling. However, due to the complex and invisible characteristics of rock microstructure, the effect of cyclic heating and cooling on rock macro/micro physical and mechanical properties still requires further investigation. In this study, to explore the microscopic mechanism underlying the variations of rock macroscopic properties during cyclic heating and cooling, uniaxial compression tests and P-wave velocity tests were conducted to obtain the macromechanical properties of red sandstone specimens subjected to varying numbers of heating and cooling cycles. Acoustic emission (AE) tests were also carried out to capture the variations in the microscopic damage process during each heating and cooling cycle. A scanning electron microscope and differential thermal analysis–thermal gravimetric analyzer were used to analyze the development of the microcracks and variations in the micrograin mass after each cyclic heating and cooling. The test results demonstrate that after being heated to 500 °C, some of the minerals (microcline, albite and calcite) in the sandstone decomposed and microcrocks developed due to the uneven thermal stress. When the sandstone was cooled in water, more microdefects were induced to the microstructure due to mineral transformations and uneven contractions, causing further deterioration to the integrity and compactness of the rock matrix. This phenomenon was also reflected in the uniaxial compression tests and AE tests. Due to the damage caused by each heating and cooling cycle, the AE hit rate decreased and the macrophysical and mechanical properties of rock deteriorated as the number of cycles increases. Comparison of the test results obtained from samples subjected to different heating and cooling cycles reveals that although each cycle could cause damage to the rock sample, the first and fifth cycles induced more severe damage, as indicated by the sharp decrease in the physical and mechanical properties of the rock after the first and fifth cycles. [ABSTRACT FROM AUTHOR]

Abstract Fracture grouting is one of the most widely used methodologies to reduce the hydraulic conductivity and enhance the strength of rock masses in geotechnical engineering (e.g., mining, civil engineering and hydraulic engineering). Understanding and controlling the migration process of grout slurry are critical to optimize the grouting process. In this paper, a grouting process simulator is generated for hydro-mechanical (HM) coupling grouting problems, linking the combined finite-discrete element method (FDEM) and a grouting flow simulator, called as FDEM-grouting. The initiation and propagation of fractures as well as the deformation of solid mass are solved by the FDEM. Meanwhile, the grout flow in fractures is modeled based on the principle of the parallel-plate model. This FDEM-grouting can consider the HM coupling effect, the stress-induced fracture aperture variation, the fracture networks evolution and the hardening of grout during the grouting process, which are rarely considered in previous studies. The present FDEM-grouting is validated by intensive numerical tests. Then, several influence factors of grout penetration are discussed. Lastly, we investigate a fracture grouting process with considering the effect of in-situ stress and the interference between grouting holes. Results show that this FDEM-grouting is potentially useful to optimize the fracture grouting process. [ABSTRACT FROM AUTHOR]