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Effects of thawing-induced softening on fracture behaviors of frozen rock

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Journal of Rock Mechanics and Geotechnical Engineering 2024年第3期16卷 979-989页

作者： Ting Wang Hailiang Jia Qiang Sun xianjun tan Liyun tang College of Geology and Environment Xi’an University of Science and TechnologyXi’an710054China College of Architecture and Civil Engineering Xi’an University of Science and TechnologyXi’an710054China State Key Laboratory of Geomechanics and Geotechnical Engineering Institute of Rock and Soil MechanicsChinese Academy of SciencesWuhan430064China

Due to the presence of ice and unfrozen water in pores of frozen rock,the rock fracture behaviors are susceptible to *** this study,the potential thawing-induced softening effects on the fracture behaviors of frozen rock is evaluated by testing the tension fracture toughness(KIC)of frozen rock at different temperatures(i.e.-20℃,-15℃,-12℃,-10℃,-8℃,-6℃,-4℃,-2℃,and 0℃).Acoustic emission(AE)and digital image correlation(DIC)methods are utilized to analyze the microcrack propagation during *** melting of pore ice is measured using nuclear magnetic resonance(NMR)*** results indicate that:(1)The KIC of frozen rock decreases moderately between-20℃ and-4℃,and rapidly between-4℃ and 0℃.(2)At-20℃ to-4℃,the fracturing process,deduced from the DIC results at the notch tip,exhibits three stages:elastic deformation,microcrack propagation and microcrack ***,at-4℃e0℃,only the latter two stages are observed.(3)At-4℃e0℃,the AE activities during fracturing are less than that at-20℃ to-4℃,while more small events are reported.(4)The NMR results demonstrate a reverse variation trend in pore ice content with increasing temperature,that is,a moderate decrease is followed by a sharp decrease and-4℃ is exactly the critical ***,we interpret the thawing-induced softening effect by linking the evolution in microscopic structure of frozen rock with its macroscopic fracture behaviors as follow:from-20℃ to-4℃,the thickening of the unfrozen water film diminishes the cementation strength between ice and rock skeleton,leading to the decrease in fracture ***-4℃ to 0℃,the cementation effect of ice almost vanishes,and the filling effect of pore ice is reduced significantly,which facilitates microcrack propagation and thus the easier fracture of frozen rocks.

关键词： Frozen sandstone Different thawing temperature Fracture toughness Microcrack propagation process Unfrozen water content

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

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Journal of Rock Mechanics and Geotechnical Engineering 2023年第10期15卷 2626-2638页

作者： Hui Li Weizhong Chen xianjun tan State Key Laboratory of Geomechanics and Geotechnical Engineering Institute of Rock and Soil MechanicsChinese Academy of SciencesWuhan430071China

Displacement-monitoring-based back analysis is a popular method for geomechanical parameter ***,due to the delayed installation of multi-point extensometers,the monitoring curve is only a part of the overall one,leading to displacement ***,the monitoring and construction time on the monitoring curve is difficult to *** the literature,the final displacement was selected for the back analysis,which could induce unreliable *** 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 *** 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 *** 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 ***,the hybrid optimization algorithm is applied to an engineering *** 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.

关键词： Rock mass Intelligent back analysis Geomechanical parameters Displacement loss Underground engineering

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

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International Journal of Mining Science and Technology 2022年第5期32卷 1087-1096页

作者： Chaoxuan Zhang xianjun tan Hongming Tian Weizhong Chen State Key Laboratory of Geomechanics and Geotechnical Engineering Institute of Rock and Soil MechanicsChinese Academy of SciencesWuhan 430071China University of Chinese Academy of Sciences Beijing 100049China

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 ***,the lengthy curing and defoaming problems caused by the cast-in-place method of large-volume foamed concrete remain *** 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 *** show that FC-PE pipes exhibit typical three-stage deformation characteristics,comprising the elastic stage,the plastic plateau,and the densification ***,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,*** the density of the foamed concrete increases,the plateau stress and energy absorption increase ***,the length of the plastic plateau and energy absorption efficiency ***,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.

关键词： Soft rock Yielding layer Foamed concrete Polyethylene pipe Lateral compression Energy absorption

Reinventing MoS2 Co-catalytic Fenton reaction:Oxygen-incorporation mediating surface superoxide radical generation

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Nano Research 2022年第3期15卷 1973-1982页

作者： xianjun tan Wenhui Ding Zhenying Jiang Linxiao Sun Yuxiong Huang Environmental Science and New Energy Technology Research Center Tsinghua-Berkeley Shenzhen Institute(TBSI)Tsinghua Shenzhen International Graduate SchoolTsinghua UniversityShenzhen 518055China

To better understand the mechanisms of hydrogen peroxide(H_(2)O_(2))’s decomposition and reactive oxygen species(ROS)’s formation on the catalyst’s surface is always a critical issue for the environmental application of Fenton/Fenton-like *** here report a new approach to activate H_(2)O_(2) in a co-catalytic Fenton system with oxygen incorporated MoS2,namely MoS_(2−x) O_(x) *** MoS_(2−x) O_(x) nanosheets assisted co-catalytic Fenton system exhibited superior degradation activity of emerging antibiotic contaminants(e.g.,sulfamethoxazole).Combining density functional theory(DFT)calculation and experimental investigation,we demonstrated that oxygen incorporation could improve the intrinsic conductivity of MoS_(2−x) O_(x) nanosheets and accelerate surface/interfacial charge transfer,which further leads to the efficacious activation of H_(2)O_(2).Moreover,by tuning the oxygen proportion in MoS_(2−x) O_(x) nanosheets,we are able to modulate the generation of ROS and further direct the oriented-conversion of H_(2)O_(2) to surface-bounded superoxide radical(·O_(2−surface)).It sheds light on the generation and transformation of ROS in the engineered system(e.g.,Fenton,Fenton-like reaction)for efficient degradation of persistent pollutants.

关键词： Co-catalytic Fenton reaction MoS2 nanosheets reactive oxygen species(ROS) superoxide radical antibiotics’degradation

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

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Journal of Rock Mechanics and Geotechnical Engineering 2022年第5期14卷 1545-1555页

作者： Zhouzhou Su xianjun tan Weizhong Chen Hailiang Jia Fei Xu State Key Laboratory of Geomechanics and Geotechnical Engineering Institute of Rock and Soil MechanicsChinese Academy of SciencesWuhan430071China University of Chinese Academy of Sciences Beijing100049China College of Architecture and Civil Engineering Xi’an University of Science and TechnologyXi’an710054China Structural Health Monitoring and Control Institute Shijiazhuang Tiedao UniversityShijiazhuang050043China

The unfrozen water content of rock during freezing and thawing has an important influence on its physical and mechanical *** 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 *** 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 *** 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 ***,the influences of Hamaker constant and surface relaxation parameter on the model results were *** 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.

关键词： Freezing and thawing Unfrozen water content Super-cooling and hysteresis Nuclear magnetic resonance(NMR) Unfrozen water calculation model Red sandstone

Revisiting the methods for gas permeability measurement in tight porous medium

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Journal of Rock Mechanics and Geotechnical Engineering 2019年第2期11卷 263-276页

作者： Diansen Yang Wei Wang Weizhong Chen xianjun tan Lige Wang State Key Laboratory of Geomechanics and Geotechnical Engineering Institute of Rock and Soil MechanicsChinese Academy of Sciences University of Chinese Academy of Sciences Geotechnical and Structural Engineering Research Center Shandong University School of Engineering University of Sheffield

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.

关键词： Permeability measurement Steady state method Pulse decay method(PDM) Pressure oscillation method(POM) Effective porosity Tight porous medium

Direct conversion of methane to methanol over Cu exchanged mordenite:Effect of counter ions

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Chinese Chemical Letters 2020年第1期31卷 235-238页

作者： Chuang Ma xianjun tan Haijiao Zhang Qun Shen Nannan Sun Wei Wei Institute of Nanochemistry and Nanobiology School of Environmental and Chemical EngineeringShanghai UniversityShanghai 200444China CAS Key Lab of Low-Carbon Conversion Science and Engineering Shanghai Advanced Research InstituteChinese Academy of SciencesShanghai 201210China School of Physical Science and Technology ShanghaiTech UniversityShanghai 201210China

Direct conversion of methane(CH4)to methanol(DMTM)is a promising,but very challenging process for the utilization of abundant CH4 as a low carbon *** this context,Cu loaded zeolites,mordenite(MOR)in particular,were recognized as the most effective system to perform *** this work,different Cu salts were used to exchange with MOR,by which the effect of counter ions on the catalytic performance towards DMTM was *** prepared catalysts were characterized and evaluated *** was found that the counter ions affected the speciation of Cu sites,probably due to their capability in extraction of protons from MOR and the influence on the hydrolysis state of the Cu2+in aqueous *** behaviors adjusted the association between Cu2+and the exchangeable protons in *** a result,varied DMTM performance was *** the used Cu salts,Cu(CH3COO)2 exchanged MOR showed the highest performance,achieving stable CH3 OH yield of 117±28μmol/g in 5 consecutive cycles,these values are among the highest for Cu loaded MOR zeolites in open publications.

关键词： Methane Methanol Zeolite Mordenite MOR Cu

Photo-induced surface frustrated Lewis pairs for promoted photocatalytic decomposition of perfluorooctanoic acid

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Frontiers of Environmental Science & Engineering 2023年第1期17卷 27-32页

作者： xianjun tan Zhenying Jiang Yuxiong Huang Tsinghua-Berkeley Shenzhen Institute(TBSI) Shenzhen International Graduate SchoolTsinghua UniversityShenzhen 518055China

Heterogeneous photocatalysis has gained substantial research interest in treating per-and polyfluoroalkyl substances(PFAS)-contaminated ***,sluggish degradation kinetics and low defluorination efficiency compromise their practical ***,we report a superior photocatalyst,defected Bi_(3)O(OH)(PO_(4))_(2),which could effectively degrade typical PFAS,perfluorooctanoic acid(PFOA),with high defluorination *** UV light irradiation could in situ generate oxygen vacancies on Bi_(3)O(OH)(PO_(4))_(2) through oxidation of the lattice hydroxyls,which further promotes the formation of Lewis acidic coordinately unsaturated bismuth ***,the Lewis acidic sites couple with the proximal surface hydroxyls to constitute the surface frustrated Lewis pairs(SFLPs).With the in-depth spectroscopic analysis,we revealed that the photo-induced SFLPs act as collection centers to effectively adsorb PFOA and endow accessible pathways to transfer photogenerated holes to PFOA ***,activation of the terminal carboxyl,a ratelimiting step for PFOA decomposition,could be easily achieved over the defected Bi_(3)O(OH)(PO_(4))_(2) *** results suggest that SFLPs exhibit great potential in developing highly efficient photocatalysts to degrade persistent organic pollutants.

关键词： Heterogeneous photocatalysis Surface frustrated Lewis pairs Perfluorooctanoic acid Defluorination efficiency Environmental remediation

A fully coupled thermo-hydro-mechanical model for unsaturated porous media

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Journal of Rock Mechanics and Geotechnical Engineering 2009年第1期1卷 31-40页

作者： Weizhong Chen xianjun tan Hongdan Yu Guojun Wu Shanpo Jia State Key Laboratory of Geomechanics and Geotechnical Engineering Institute of Rock and Soil Mechanics Chinese Academy of Sciences Wuhan 430071 China

In examining potential host rocks for such purposes as the disposal of high-level radioactive wastes,it is important to understand the coupled thermo-hydro-mechanical（THM） behavior of a porous medium.A rigorous and fully unified coupled thermo-hydro-mechanical model for unsaturated porous media is required to simulate the complex coupling mechanisms *** on modified Darcy＇s and Fourier＇s laws,equations of mechanical equilibrium,mass conservation and energy conservation are derived by introducing void ratio and volumetric liquid water content into the *** newly derived model takes into account the effects of temperature on the dynamic viscosity of liquid water and void ratio,the influence of liquid flow on temperature gradient（thermo-osmosis）,the influence on mass and heat conservation equations,and the influence of heat flow on water pressure gradient and thermal *** new coupled THM constitutive model is constructed by a finite element program and is used to simulate the coupled behavior of a tunnel during excavation,ventilation and concrete lining *** and gas engineering,underground disposal of nuclear waste and tunnel engineering may be benefited from the development of the new model.

关键词： porous media unsaturated media coupled thermo-hydro-mechanical (THM) model