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Thermo-hydro-mechanical behavior of clay rock for deep geological disposal of high-level radioactive waste

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Journal of Rock Mechanics and Geotechnical Engineering 2018年第5期10卷 992-1008页

作者： chun-liang zhang Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) Repository Safety Research Division Theodor-Heuss-Str 4 Braunschweig 38122 Germany

In the context of deep geological disposal of radioactive waste in clay formations, the thermo-hydro- mechanical （THM） behavior of the indurated Callovo-Oxfordian and Opalinus clay rocks has been extensively investigated in our laboratory under repository relevant conditions：（1） rock stress covering the range from the lithostatic state to redistributed levels after excavation; （2） variation of the humidity in the openings due to ventilation as well as hydraulic drained and undrained boundary conditions; （3） gas generation from corrosion of metallic components within repositories; and （4） thermal loading from high-level radioactive waste up to the designed maximum temperature of 90 ~C and even beyond to 150 ~C, Various important aspects concerning the long-term barrier functions of the clay host rocks have been studied：（1） fundamental concept for effective stress in the porous clay-water system; （2） stress- driven deformation and damage as well as resulting permeability changes; （3） moisture influences on mechanical properties; （4） self-sealing of fractures under mechanical load and swelling]slaking of clay minerals upon water uptake; （5） gas migration in fractured and resealed claystones; and （6） thermal impact on the hydro-mechanical behavior and properties, Major findings from the investigations are summarized in this paper,

关键词： Repository Clay rock Deformability Swelling Self-sealing Water permeability Gas migration Thermal impact

Examination of effective stress in clay rock

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Journal of Rock Mechanics and Geotechnical Engineering 2017年第3期9卷 97-107页

作者： chun-liang zhang Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) Braunschweig 38122 Germany

This paper examines the effective stress in indurated clay rock theoretically and experimentally.A stress concept is derived from the analysis of the microstructure and of the pore water in the highly-indurated Callovo-Oxfordian and Opalinus clay rocks,and subsequently validated by various experiments performed on these *** concept suggests that the interparticle or effective stress in a dense clay ewater system is transferred through both the adsorbed interparticle pore water in narrow pores and the solidesolid contact between non-clay mineral *** experiments show that the adsorbed pore water in the claystones is capable of bearing deviatoric effective stresses up to the failure *** applied stresses are for the most part or even totally transferred by the bound pore water,*** swelling pressure in the interparticle bound pore water is almost equivalent to the effective *** stress concept provides a reasonable view to the nature of the effective stress in argillaceous rock and forms the fundamental basis for studies of the hydro-mechanical properties and processes in clay formations.

关键词： Clay rock Stress analysis Effective stress Swelling pressure Experiment

Mechanical behavior of sandy facies of Opalinus Clay under different loadconditions

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Journal of Rock Mechanics and Geotechnical Engineering 2020年第2期12卷 223-241页

作者： chun-liang zhang Ben Laurich Gesellschaft für Anlagen-und Reaktorsicherheit(GRS) BraunschweigGermany Federal Institute for Geosciences and Natural Resources(BGR) HannoverGermany

The mechanical behavior of sandy facies of Opalinus Clay at the Mont Terri underground rock laboratory(URL)in Switzerland was investigated with drained and undrained triaxial compression and extension,cyclic compression,and creep *** were taken from boreholes drilled parallel to *** of the samples were reconditioned to minimize sampling effects of desaturation and *** compression was accomplished by increasing axial stress at constant radial *** extension was carried out by increasing radial stress at constant axial ***,extension was also achieved by simultaneously increasing radial stress and decreasing axial stress under constant mean *** test results showed elastoplastic stress-strain behavior with volumetric compaction until onset of dilatancy at high deviatoric stresses above 80%-90%of the peak failure *** strength is dependent upon load path and mean *** strength under triaxial compression is higher than that under *** respective strength increases with increasing mean *** enhances the stiffness and strength of the *** deformation and strength of the elaystone are *** constant deviatoric stress,the claystone crept continuously with time,which can be characterized by a transient phase and a following stationary phase,and even a tertiary phase at high deviatoric stresses to rupture.

关键词： Clay rock Compression Extension Creep Stiffness

Self-sealing of fractures in indurated claystones measured by water and gas flow

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Journal of Rock Mechanics and Geotechnical Engineering 2023年第1期15卷 227-238页

作者： chun-liang zhang Jean Talandier Gesellschaft für Anlagen-und Reaktorsicherheit(GRS) Braunschweig38122Germany Agence nationale pour la gestion des déchets radioactifs(ANDRA) Châtenay-Malabry cedex92298France

Self-sealing of fractures in the indurated Callovo-Oxfordian(COX)and Opalinus(OPA)claystones,which are considered as host rocks for disposal of radioactive waste,was investigated on artificially fractured *** samples were extracted from four lithological facies relatively rich in clay mineral,carbonate and quartz,*** self-sealing of fractures was measured by fracture closure,water permeability variation,gas penetration,and recovery of gas-induced *** of the fractured samples exhibited a dramatic reduction inwater permeability to low levels that is close to that of intact rock,depending on their mineralogical composition,fracture intensity,confining stress,and load *** self-sealing capacity of the clay-rich samples is higher than that of the carbonate-rich and sandy *** effects of sample size and fracture intensity were *** sealed fractures become gas-tight for certain in-jection ***,the measured gas breakthrough pressures are still lower than the confining *** gas-induced pathways can recover when contacting *** important findings imply that fractures in such indurated claystones can effectively recover to hinder water transport but allow gas release under relatively low pressures without compromising the rock integrity.

关键词： Claystone Self-sealing of fracture Fracture closure Water permeability Gas breakthrough pressure Resealing of gas pathway

The stress-strain-permeability behaviour of clay rock during damage and recompaction

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Journal of Rock Mechanics and Geotechnical Engineering 2016年第1期8卷 16-26页

作者： chun-liang zhang Gesellschaft für Anlagen-und Reaktorsicherheit(GRS)mbH Braunschweig38122Germany

Characterisation and understanding of the stressestrainepermeability behaviour of a clay host rock during damage and recompaction are essential for prediction of excavation damaged zone and for assessment of its impact on the repository safety. This important issue has been experimentally studied in triaxial compression tests on the Callovo-Oxfordian clay rock in this study. The samples were sequentially loaded by(1) hydrostatic precompaction to close up sampling-induced microcracks,(2)applying deviatoric stresses to determine damage and permeability changes, and(3) recompression along different loading paths to examine reversibility of the damage. The critical stress conditions at the onset of dilatancy, permeability percolation, failure strength, and residual strength are determined. An empirical model is established for fracturing-induced permeability by considering the effects of connectivity and conductivity of microcracks. The cubic law is validated for the variation of permeability of connected fractures with closure. The experiments and results are also presented and discussed.

关键词： Clay rock Deformation Damage Compaction Permeability

Sealing of fractures in claystone

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Journal of Rock Mechanics and Geotechnical Engineering 2013年第3期5卷 214-220,251页

作者： chun-liang zhang Gesellschaft für Anlagen-und Reaktorsicherheit (GRS)

The sealing behavior of fractures in clay rocks for deep disposal of radioactive waste has been comprehensively investigated at the GRS laboratory. Various sealing experiments were performed on strongly cracked samples of different sizes from the Callovo-Oxfordian argillite and the Opalinus clay under rel- evant repository conditions. The fractured samples were compacted and flowed through with gas or synthetic pore-water under confining stresses up to 18 MPa and elevated temperatures from 20 ℃ to 90℃. Sealing of fractures was quantified by measurements of their closure and permeability. Under the applied thermo-hydro-mechanical （THM） conditions, significant fracture closure and permeability decrease to very low levels of 10^-19 to 10^-21 m^2 were observed within time periods of months to years. The properties of the resealed claystones are comparable with those of the intact rock mass. All test results suggest high sealing potentials of the studied claystones.

关键词： Clay rock Damage Fracture closure Permeability Sealing experiment Nuclear waste repository

Thermal effects on clay rocks for deep disposal of high-level radioactive waste

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Journal of Rock Mechanics and Geotechnical Engineering 2017年第3期9卷 81-96页

作者： chun-liang zhang Nathalie Conil Gilles Armand Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) Braunschweig 38122 Germany Agence nationale pour la gestion des déchets radioactifs (Andra) Bure 55290 France

Thermal effects on the Callovo-Oxfordian and Opalinus clay rocks for hosting high-level radioactive waste were comprehensively investigated with laboratory and in situ experiments under repository relevant conditions:(1) stresses covering the range from the initial lithostatic state to redistributed levels after excavation,(2) hydraulic drained and undrained boundaries, and(3) heating from ambient temperature up to 90℃-120℃ and a subsequent cooling phase. The laboratory experiments were performed on normal-sized and large hollow cylindrical samples in various respects of thermal expansion and contraction, thermally-induced pore water pressure, temperature influences on deformation and strength, thermal impacts on swelling, fracture sealing and permeability. The laboratory results obtained from the samples are consistent with the in situ observations during heating experiments in the underground research laboratories at Bure and Mont-Terri. Even though the claystones showed significant responses to thermal loading, no negative effects on their favorable barrier properties were observed.

关键词： Clay rock Thermal effects Pore pressure Deformation Strength Permeability Sealing of fractures Repository

Microvessel density at different levels of normal or injured bile duct in dogs and its surgical implications

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Hepatobiliary & Pancreatic Diseases International 2011年第1期10卷 83-87页

作者： Lin Geng,Ding Luo,Hao-chun zhang,liang-Song Zhao and De-Ke Qing Department of Hepatobiliary Surgery,Kunming General Hospital of PLA,Kunming 650032,China Department of Hepatobiliary Surgery Kunming General Hospital of PLA Kunming 650032 China

BACKGROUND:Ischemic recurrent stricture after surgical repair for iatrogenic bile duct injury(BDI)remains a challenge in clinical *** present study was designed to investigate whether ischemia is universal and of varied severity at different levels of the proximal bile duct after BDI. METHODS:A total of 30 beagle dogs were randomly divided into control,BDI,and BDI-repaired *** BDI animal model was established based on the classic pattern of laparoscopic cholecystectomy-related *** animals were sacrificed on postoperative day 15,and bile duct tissue was harvested to assess microvessel density(MVD)at selected levels of the normal,post-BDI and BDI-repaired bile duct with the CD34 immunohistochemistry technique. RESULTS:In the control group,MVD at level H(high level) was remarkably higher than that at level L(low level).No significant difference was found between MVDs at levels H and M(middle level),as well as at levels M and ***, the tendency was noted that the closer the level to the hilus, the greater the MVD at that *** both the BDI and BDI-repaired groups,MVDs at level H were generally greater than those at level L,despite the unremarkable differences between MVDs at neighboring *** these two groups,a similar tendency of MVD distribution to that in the control group was found;the closer the level to the injury site,the lower was the MVD at that ***,compared with the MDVs at the levels M and L in the control group,MVDs at the corresponding levels in the BDI and BDI-repaired groups were all remarkably reduced(P<0.05).In addition,MVDs at all three levels in the BDI group significantly declined further after BDI ***:After BDI,universal ischemic damage in the injured proximal bile duct develops close to the injury site, while close to the hilus,ischemia is relatively *** hepaticojejunostomy,rather than low biloenterostomy or end-to-end duct anastomosis,should be recommended for BDI *** care

关键词： microvessel density bile duct injury laparoscopic cholecystectomy ischemia reconstruction

Optimization of three-dimensional boiling enhancement structure at evaporation surface for high power light emitting diode

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Transactions of Nonferrous Metals Society of China 2018年第7期28卷 1405-1413页

作者： Jian-hua XIANG Chao ZHOU chun-liang zhang Gui-yun LIU Cong-gui CHEN Wei ZHOU School of Mechanical and Electric Engineering Guangzhou UniversityGuangzhou 510006China Department of Mechanical and Electrical Engineering Xiamen UniversityXiamen 361005China

A theoretical model of phase change heat sink was established in terms of thermal resistance network. The influence of different parameters on the thermal resistance was analyzed and the crucial impact factors were determined. Subsequently, the forming methods including ploughing-extrusion and stamping method of boiling enhancement structure at evaporation surface were investigated, upon which three-dimensional microgroove structure was fabricated to improve the efficiency of evaporation. Moreover, the crucial parameters related to the fabrication of miniaturized phase change heat sink were optimized. The heat transfer performance of the heat sink was tested. Results show that the developed phase change heat sink has excellent heat transfer performance and is suitable for high power LED applications.

关键词： high power LED phase change heat sink ploughing-extrusion boiling enhancement three-dimensional microgroove