Study of hydro-mechanical behaviours of rough rock fracture with shear dilatancy and asperities using shear-flow model

The geometric properties of fracture surfaces significantly influence shear-seepage in rock fractures,introducing complexities to fracture modelling.The present study focuses on the hydro-mechanical behaviours of rough rock fractures during shear-seepage processes to reveal how dilatancy and fracture asperities affect these phenomena.To achieve this,an improved shear-flow model(SFM)is proposed with the incorporation of dilatancy effect and asperities.In particular,shear dilatancy is accounted for in both the elastic and plastic stages,in contrast to some existing models that only consider it in the elastic stage.Depending on the computation approaches for the peak dilatancy angle,three different versions of the SFM are derived based on Mohr-Coulomb,joint roughness coefficient-joint compressive strength(JRC-JCS),and Grasselli’s theories.Notably,this is a new attempt that utilizes Grasselli’s model in shearseepage analysis.An advanced parameter optimization method is introduced to accurately determine model parameters,addressing the issue of local optima inherent in some conventional methods.Then,model performance is evaluated against existing experimental results.The findings demonstrate that the SFM effectively reproduces the shear-seepage characteristics of rock fracture across a wide range of stress levels.Further sensitivity analysis reveals how dilatancy and asperity affect hydraulic properties.The relation between hydro-mechanical properties(dilatancy displacement and hydraulic conductivity)and asperity parameters is analysed.Several profound understandings of the shear-seepage process are obtained by exploring the phenomenon under various conditions.

Estimation of tunnel axial orientation in the interlayered rock mass using a comprehensive algorithm

The axial selection of tunnels constructed in the interlayered soft-hard rock mass affects the stability and safety during construction.Previous optimization is primarily based on experience or comparison and selection of alternative values under specific geological conditions.In this work,an intelligent optimization framework has been proposed by combining numerical analysis,machine learning(ML)and optimization algorithm.An automatic and intelligent numerical analysis process was proposed and coded to reduce redundant manual intervention.The conventional optimization algorithm was developed from two aspects and applied to the hyperparameters estimation of the support vector machine(SVM)model and the axial orientation optimization of the tunnel.Finally,the comprehensive framework was applied to a numerical case study,and the results were compared with those of other studies.The results of this study indicate that the determination coefficients between the predicted and the numerical stability evaluation indices(STIs)on the training and testing datasets are 0.998 and 0.997,respectively.For a given geological condition,the STI that changes with the axial orientation shows the trend of first decreasing and then increasing,and the optimal tunnel axial orientation is estimated to be 87.This method provides an alternative and quick approach to the overall design of the tunnels.

Recent developments in superjunction power devices

Abstract:Superjunction(SJ)is one of the most innovative concepts in the field of power semiconductor devices and is often referred to as a"milestone"in power MOS.Its balanced charge field modulation mechanism breaks through the strong dependency between the doping concentration in the drift region and the breakdown voltage V_(B)in conventional devices.This results in a reduction of the trade-off relationship between specific on-resistance R_(on,sp)and V_(B)from the conventional R_(on,sp)∝V_(B)^(2.5)to R_(on,sp)∝W·V_(B)^(1.32),and even to R_(on,sp)∝W·V_(B)^(1.03).As the exponential term coefficient decreases,R_(on,sp)decreases with the cell width W,exhibiting a development pattern reminiscent of"Moore's Law".This paper provides an overview of the latest research developments in SJ power semiconductor devices.Firstly,it introduces the minimum specific on-resistance R_(on,min)theory of SJ devices,along with its combination with special effects like 3-D depletion and tunneling,discussing the development of R_(on,min)theory in the wide bandgap SJ field.Subsequently,it discusses the latest advancements in silicon-based and wide bandgap SJ power devices.Finally,it introduces the homogenization field(HOF)and high-K voltage-sustaining layers derived from the concept of SJ charge balance.SJ has made significant progress in device performance,reliability,and integration,and in the future,it will continue to evolve through deeper integration with different materials,processes,and packaging technologies,enhancing the overall performance of semiconductor power devices.

On the critical particle size of soil with clogging potential in shield tunneling

Shield tunneling is easily obstructed by clogging in clayey strata with small soil particles.However,soil clogging rarely occurs in strata with coarse-grained soils.Theoretically,a critical particle size of soils should exist,below which there is a high risk of soil clogging in shield tunneling.To determine the critical particle size,a series of laboratory tests was carried out with a large-scale rotary shear apparatus to measure the tangential adhesion strength of soils with different particle sizes and water contents.It was found that the tangential adhesion strength at the soilesteel interface gradually increased linearly with applied normal pressure.When the particle size of the soil specimen was less than 0.15 mm,the interfacial adhesion force first increased and then decreased as the water content gradually increased;otherwise,the soil specimens did not manifest any interfacial adhesion force.The amount of soil mass adhering to the steel disc was positively correlated with the interfacial adhesion force,thus the interfacial adhesion force was adopted to characterize the soil clogging risk in shield tunneling.The critical particle size of soils causing clogging was determined to be 0.15 mm.Finally,the generation mechanism of interfacial adhesion force was explored for soils with different particle sizes to explain the critical particle size of soil with clogging risk in shield tunneling.

Real-time prediction of mechanical behaviors of underwater shield tunnel structure using machine learning method based on structural health monitoring data

Predicting the mechanical behaviors of structure and perceiving the anomalies in advance are essential to ensuring the safe operation of infrastructures in the long run.In addition to the incomplete consideration of influencing factors,the prediction time scale of existing studies is rough.Therefore,this study focuses on the development of a real-time prediction model by coupling the spatio-temporal correlation with external load through autoencoder network(ATENet)based on structural health monitoring(SHM)data.An autoencoder mechanism is performed to acquire the high-level representation of raw monitoring data at different spatial positions,and the recurrent neural network is applied to understanding the temporal correlation from the time series.Then,the obtained temporal-spatial information is coupled with dynamic loads through a fully connected layer to predict structural performance in next 12 h.As a case study,the proposed model is formulated on the SHM data collected from a representative underwater shield tunnel.The robustness study is carried out to verify the reliability and the prediction capability of the proposed model.Finally,the ATENet model is compared with some typical models,and the results indicate that it has the best performance.ATENet model is of great value to predict the realtime evolution trend of tunnel structure.

Spatial deduction of mining-induced stress redistribution using an optimized non-negative matrix factorization model

Investigation of mining-induced stress is essential for the safety of coal production.Although the field monitoring and numerical simulation play a significant role in obtaining the structural mechanical behaviors,the range of monitoring is not sufficient due to the limits of monitoring points and the associated numerical result is not accurate.In this study,we aim to present a spatial deduction model to characterize the mining-induced stress distribution using machine learning algorithm on limited monitoring data.First,the framework of the spatial deduction model is developed on the basis of non-negative matrix factorization(NMF)algorithm and optimized by mechanical mechanism.In this framework,the spatial correlation of stress response is captured from numerical results,and the learned correlation is employed in NMF as a mechanical constrain to augment the limited monitoring data and obtain the overall mechanical performances.Then,the developed model is applied to a coal mine in Shandong,China.Experimental results show the stress distribution in one plane is derived by several monitoring points,where mining induced stress release is observed in goaf and stress concentration in coal pillar,and the intersection point between goaf and coal seam is a sensitive area.The indicators used to evaluate the property of the presented model indicate that 83%mechanical performances have been captured and the deduction accuracy is about 92.9%.Therefore,it is likely that the presented deduction model is reliable.

An integrated split and dummy gates MOSFET with fast turn-off and reverse recovery characteristics

A power MOSFET with integrated split gate and dummy gate(SD-MOS) is proposed and demonstrated by the TCAD SENTAURUS.The split gate is surrounded by the source and shielded by the dummy gate.Consequently,the coupling area between the split gate and the drain electrode is reduced,thus the gate-to-drain charge(Q_(GD)),reverse transfer capacitance(C_(RSS)) and turn-off loss(E_(off)) are significantly decreased.Moreover,the MOS-channel diode is controlled by the dummy gate with ultra-thin gate oxide t_(ox),which can be turned on before the parasitic P-base/N-drift diode at the reverse conduction,then the majority carriers are injected to the N-drift to attenuate the minority injection.Therefore,the reverse recovery charge(Q_(RR)),time(T_(RR)) and peak current(I_(RRM)) are effectively reduced at the reverse freewheeling state.Additionally,the specific on-resistance(R_(on,sp)) and breakdown voltage(BV) are also studied to evaluate the static properties of the proposed SD-MOS.The simulation results show that the Q_(GD) of 6 nC/cm^(2),the C_(RSS) of 1.1 pF/cm^(2) at the V_(DS) of 150 V,the QRR of 1.2 μC/cm^(2) and the R_(on,sp) of 8.4 mΩ·cm^(2) are obtained,thus the figures of merit(FOM) including Q_(GD) ×R_(on,sp) of50 nC·mΩ,E_(off) × R_(on,sp) of 0.59 mJ·mΩ and the Q_(RR) × R_(on,sp) of 10.1 μC·mΩ are achieved for the proposed SD-MOS.

Displacement-based back analysis of mitigating the effects of displacement loss in underground engineering

Displacement-monitoring-based back analysis is a popular method for geomechanical parameter estimation.However,due to the delayed installation of multi-point extensometers,the monitoring curve is only a part of the overall one,leading to displacement loss.Besides,the monitoring and construction time on the monitoring curve is difficult to determine.In the literature,the final displacement was selected for the back analysis,which could induce unreliable results.In this paper,a displacement-based back analysis method to mitigate the influence of displacement loss is developed.A robust hybrid optimization algorithm is proposed as a substitute for time-consuming numerical simulation.It integrates the strengths of the nonlinear mapping and prediction capability of the support vector machine(SVM)algorithm,the global searching and optimization characteristics of the optimized particle swarm optimization(OPSO)algorithm,and the nonlinear numerical simulation capability of ABAQUS.To avoid being trapped in the local optimum and to improve the efficiency of optimization,the standard PSO algorithm is improved and is compared with other three algorithms(genetic algorithm(GA),simulated annealing(SA),and standard PSO).The results indicate the superiority of OPSO algorithm.Finally,the hybrid optimization algorithm is applied to an engineering project.The back-analyzed parameters are submitted to numerical analysis,and comparison between the calculated and monitoring displacement curve shows that this hybrid algorithm can offer a reasonable reference for geomechanical parameters estimation.

Mechanical properties and associated seismic isolation effects of foamed concrete layer in rock tunnel

Foamed concrete has a good energy absorption capability and can be used as seismic isolation material for tunnels. This study aims to investigate the mechanical properties and associated seismic isolation effects of foamed concrete layer in rock tunnel. For this, a series of uniaxial/triaxial compression tests was conducted to understand the effects of concrete density, confining stress and strain rate on the mechanical properties of foamed concrete. The direct shear tests were also performed to investigate the effects of concrete density and normal stress on the nonlinear behaviors of foamed concrete layer-lining interface. The test results showed that the mechanical properties of foamed concrete are significantly influenced by the concrete density. The foamed concrete also has high volumetric compressibility and strain-rate dependence. The peak stress. residual stress. shear stiffness and residual friction coefficient of the foamed concrete layer-lining interface are influenced by the foamed concrete density and normal stress applied. Then, a crushable foam constitutive model was constructed using ABAQUS software and a composite exponential model was also established to study the relationship between shear stress and shear displacement of the interface, in which their parameters were fitted based on the experimental results. Finally, a parametric analysis using the finite element method(FEM) was conducted to understand the influence of foamed concrete layer properties on the seismic isolation effect, including the density and thickness of the layer as well as the shear stiffness and residual friction coefficient of the interface. It was revealed that lower density and greater thickness in addition to smaller shear stiffness or residual friction coefficient of the foamed concrete layer could yield better seismic isolation effect, and the influences of the first two tend to be more significant.

Revisiting the methods for gas permeability measurement in tight porous medium

Permeability is a key parameter to describe fluid transport properties of porous medium; however, the permeability measurement is extremely difficult for tight porous medium, e.g. fine-grained rock or dense soil. In this paper, three methods for gas permeability measurement, i.e. steady state method, pulse decay method(PDM) and pressure oscillation method(POM), are first reviewed and then their advantages and drawbacks are discussed. Both analytical and numerical solutions of gas permeability are presented for the tight porous medium. The results show that the analytical method is relatively simple but only valid under certain conditions, whilst the numerical method is more robust and generic, which can take into account several factors such as porosity, saturation, gas leakage, and unconventional boundary conditions. The influence of the effective porosity on the permeability determination is further analyzed using the proposed numerical method. In this study, new pressure data interpretation procedures for PDM and POM are proposed, and the obtained results can serve as a guidance to define a proper method for permeability measurement of the tight porous medium.

Lateral compression and energy absorption of foamed concrete-filled polyethylene circular pipe as yielding layer for high geo-stress soft rock tunnels

Foamed concrete as energy absorption material for high geo-stress soft rock tunnels has been proven to be feasible due to its high compressibility and lightweight.However,the lengthy curing and defoaming problems caused by the cast-in-place method of large-volume foamed concrete remain unsolved.In this study,we propose a novel energy absorber composed of foamed concrete-filled polyethylene(FC-PE)pipe and analyze its deformation and energy absorption capacity via quasi-static lateral compression experiments.Results show that FC-PE pipes exhibit typical three-stage deformation characteristics,comprising the elastic stage,the plastic plateau,and the densification stage.Furthermore,the plateau stress,energy absorption,and specific energy absorption of the specimens are 0.81–1.91 MPa,164–533 J,and 1.4–3.6 J/g,respectively.As the density of the foamed concrete increases,the plateau stress and energy absorption increase significantly.Conversely,the length of the plastic plateau and energy absorption efficiency decrease.Moreover,based on the vertical slice method,progressive compression of core material,and the 6 plastic hinges deformation mechanism of the pipe wall,a theoretical calculation method for effective energy absorption is established and achieves good agreement with experimental results,which is beneficial to the optimization of the composite structure.

Experimental study on the physico-mechanical properties of Tamusu mudstone — A potential host rock for high-level radioactive waste in Inner Mongolia of China

Tamusu mudstone, located in Bayin Gobi Basin in Inner Mongolia of China, has been selected as a potential host rock for high-level radioactive waste(HLW) disposal in China. A series of tests has been carried out, including X-ray diffraction(XRD) tests, scanning electron microscopy(SEM) tests, disintegration tests, permeability tests and triaxial compression tests, to estimate the physico-mechanical properties of Tamusu mudstone in this work. The mineral composition of Tamusu mudstone was analyzed and it was considered as a stable rock due to its low disintegration rate, i.e. approximately 0.11%after several wet/dry cycles. Based on the results of permeability test, it was found that Tamusu mudstone has a low permeability, with the magnitude of about 10—20m^(2). The low permeability makes the mudstone well prevent nuclide migration and diffusion, and might be influenced by temperature.The triaxial tests show that Tamusu mudstone is a stiff mudstone with high compressive strength, which means that the excavation disturbed zone would be smaller compared to other types of mudstone due to construction and operation of HLW repositories. Finally, the properties of Tamusu mudstone were compared with those of Opalinus clay, Callovo-Oxfordian(COx) argillite, and Boom clay to further discuss the possibility of using Tamusu mudstone as a potential nuclear waste disposal medium.

A model of unfrozen water content in rock during freezing and thawing with experimental validation by nuclear magnetic resonance

The unfrozen water content of rock during freezing and thawing has an important influence on its physical and mechanical properties.This study presented a model for calculating the unfrozen water content of rock during freezing and thawing process,considering the influence of unfrozen water film and rock pore structure,which can reflect the hysteresis and super-cooling effects.The pore size distribution cu rves of red sandsto ne and its unfrozen water conte nt under different temperatures during the freezing and thawing process were measured using nuclear magnetic resonance(NMR) to validate the proposed model.Comparison between the experimental and calculated results indicated that the theoretical model accu rately reflected the water content change law of red sandstone during the freezing and thawing process.Furthermore,the influences of Hamaker constant and surface relaxation parameter on the model results were examined.The results showed that the appropriate magnitude order of Hamaker constant for the red sandstone was 10J to 10J;and when the relaxation parameter of the rock surface was within 25-30 μm/ms,the calculated unfrozen water content using the proposed model was consistent with the experimental value.

Characterization of microstructural features of Tamusu mudstone

Tamusu mudstone formation, located in the Alxa area in western Inner Mongolia, is considered a potential host formation for high-level radioactive waste(HLW) underground disposal in China. In this study, complementary analyses with X-ray diffraction(XRD), field emission scanning electron microscopy(FE-SEM), mercury intrusion porosimetry(MIP), and N_(2) physisorption isotherm were conducted on the Tamusu mudstone to characterize its physical characteristics and microstructural features, such as mineral compositions and pore structure. Several minerals, including carbonates, feldspar, clays and analcime, were identified in Tamusu mudstone by XRD. Images from FE-SEM show that pores in the Tamusu mudstone were dominantly on nanometer scale and generally located within their mineral matrix or at the interface with non-porous minerals. The combination of the MIP and N_2 physisorption curves indicated that the Tamusu mudstone has diverse pore sizes, a porosity varying from 2.34% to 2.84%, and a total pore volume in the range of 0.0065—0.0222 cm^(3)/g with the average pore diameter ranging from 9.6 nm to 19.23 nm. The specific surface area measured by MIP(2.572—5.861 m^(2)/g) was generally higher than that by N_(2) physisorption(1.29—3.04 m^(2)/g), due to the pore network effect, pore shape(e.g. ink-bottle shape), or technique limits. The results related to pore information can be applied as an input in the future to model single-or multi-phase fluid flow and the transport of radionuclides in porous geomedium by migration and diffusion.

Multi-scale modelling of gas flow in nanoscale pore space with fractures

In this work,a multi-scale pore network with fractures is developed against experimental data in a wide range of degrees of water saturation.The pore network is constructed based on the measured microstructure information at several length scales.The gas transport is predicted by different gas transport equations(e.g.Javadpour,dusty gas model(DGM),Civan and Klinkenberg),which can consider the fundamental physics mechanisms in tight porous media,such as Knudsen diffusion and viscous flow.Then,the model is applied to simulating the gas permeability of the Callovo-Oxfordian(COx)claystone.The predicted gas permeability is basically in good agreement with the experimental data under different degrees of water saturation.Then the effects of micro-fissures are studied.The results suggest that this model can predict the gas flow in other tight porous media as well and can be applied to other fields such as carbon capture and storage.

PAM-Expanded Streptococcus thermophilus Cas9 C-to-T and C-to-G Base Editors for Programmable Base Editing in Mycobacteria

New therapeutic strategies for the rapid and effective treatment of drug-resistant tuberculosis are highly desirable,and their development can be drastically accelerated by facile genetic manipulation methods in Mycobacterium tuberculosis(M.tuberculosis).Clustered regularly interspaced short palindromic repeat(CRISPR)base editors allow for rapid,robust,and programmed single-base substitutions and gene inactivation,yet no such systems are currently available in M.tuberculosis.By screening distinct CRISPR base editors,we discovered that only the unusual Streptococcus thermophilus CRISPR associated protein 9(St1Cas9)cytosine base editor(CBE)-but not the widely used Streptococcus pyogenes Cas9(SpCas9)or Lachnospiraceae bacterium Cpf1(LbCpf1)CBEs-is active in mycobacteria.Despite the notable C-to-T conversions,a high proportion of undesired byproducts exists with St1Cas9 CBE.We therefore engineered St1Cas9 CBE by means of uracil DNA glycosylase inhibitor(UGI)or uracil DNA glycosylase(UNG)fusion,yielding two new base editors(CTBE and CGBE)capable of C-to-T or C-to-G conversions with dramatically enhanced editing product purity and multiplexed editing capacity in Mycobacterium smegmatis(M.smegmatis).Because wild-type St1Cas9 recognizes a relatively strict protospacer adjacent motif(PAM)sequence for DNA targeting,we engineered a PAM-expanded St1Cas9 variant by means of structureguided protein engineering for the base editors,substantially broadening the targeting scope.We first developed and characterized CTBE and CGBE in M.smegmatis,and then applied CTBE for genome editing in M.tuberculosis.Our approaches significantly reduce the efforts and time needed for precise genetic manipulation and will facilitate functional genomics,antibiotic-resistant mechanism study,and drugtarget exploration in M.tuberculosis and related organisms.

A snapback-free TOL-RC-LIGBT with vertical P-collector and N-buffer design

A reverse-conducting lateral insulated-gate bipolar transistor （NI.2-LltJlS｜） with a trench oxide layer （IUL）, teaturlng a vertical N-buffer and P-collector is proposed. Firstly, the TOL enhances both of the surface and bulk electric fields of the N-drift region, thus the breakdown voltage （BV） is improved. Secondly, the vertical N-buffer layer increases the voltage drop VpN of the P-collector/N-buffer junction, thus the snapback is suppressed. Thirdly, the P-body and the vertical N-buffer act as the anode and the cathode, respectively, to conduct the reverse current, thus the inner diode is integrated. As shown by the simulation results, the proposed RC-LIGBT exhibits trapezoidal electric field distribution with BV of 342.4 V, which is increased by nearly 340% compared to the conventional RC-LIGBT with triangular electric fields of 100.2 V. Moreover, the snapback is eliminated by the vertical N-buffer layer design, thus the reliability of the device is improved.

Effect of nonlinear translations on the pulsation of cavitation bubbles

The pulsations and translations of cavitation bubbles obey combined ordinary differential equations,and their nonlinearities are studied by the bifurcation diagram and the phase diagram in a strong ultrasonic field.Bubble pulsation can change regularly or irregularly with changing driving pressure in the time domain.The bifurcation diagrams of the pulsation versus driving pressure show that the pulsations and translations of bubbles have nonlinear characteristics,and the nonlinear translations of bubbles can disorder the pulsations for certain parameters.Disorder of the pulsation can also be caused by nonlinear pulsation itself.In addition,the phase diagrams also show that the nonlinear translations make a large contribution to the pulsations.The same result can also be obtained when the ambient radii of two bubbles are different.

Characteristics on Seawater Corrosion of Intensely Weathered Surrounding Rock of Subsea Tunnel

Existing studies on the durability of subsea tunnel mainly focus on the concrete deterioration and steel corrosion,while there are few on the infuence of mechanical properties deterioration of surrounding rock on the durability of sub-sea tunnel.To improve the accuracy of long-term stability prediction,seawater corrosion tests of intensely weathered surounding rock of subsea tunnel are car-ried out.In this study,the strength characteristics of remolded samples of inten-sely weathered granite under different seawater concentrations are investigated,the strength attenuation equation under seawater corrosion is established,and the chemical damage evolution equation and model parameters are formulated,The findings provides the basis for analyzing the influence of corosion and weak-ening of surrounding rock on the durability of tunnel within the operation period.

高邮市学龄前儿童体质训练10年前后体质指标比较

目的:比较体质干预训练10年前、后学龄前儿童体质指标,观察训练效果,探索有效的训练模式,促进儿童体质发育。方法:开展学龄前儿童体质训练,比较10年前后学龄前儿童体质指标。结果:形态指标:6岁组儿童身高、体重2018年均优于2008年,差异有统计学意义,其余年龄组均无差异。素质指标:2018年各项素质指标均优于2008年,3岁组6项指标差异均无统计学意义;3.5岁～6岁组,除3.5岁、4岁组走平衡木无差异外,其余年龄组各项素质指标差异均有统计学意义。结论:开展学龄前儿童体质训练,能够提高儿童身体素质,促进儿童健康发展。