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Phenomenological behavior of rock salt:On the influence of laboratory conditions on the dilatancy onset

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Journal of Rock Mechanics and Geotechnical Engineering 2019年第4期11卷 723-738页

作者： A.Rouabhi P.Labaune M.Tijani N.Gatelier G.Hevin MINES ParisTech PSL Research UniversityCentre de Geosciences35 rue St HonoreFontainebleau77300France Geostock Entrepose 2 rue des MartinetsRueil-Malmaison92500France Storengy 12 rue Raoul NordlingBois-Colombes92274France

Recently,stress-based dilatancy criteria have become essential tools to design underground facilities in salt formations such as gas storage caverns.However,these criteria can depend critically on the volumetric strain measurements used to deduce the dilatancy onset.Results from conventional triaxial compression tests can show different volumetric behavior depending on the loading conditions,as well as on the measurement techniques.In order to obtain a quantitative understanding of this problem,an experimental program was carried out and the testing procedure was investigated numerically under homogeneous and heterogeneous stress states.The experimental results showed that the deviatoric stress corresponding to the dilatancy onset was significantly dependent on the measurement techniques.With a heterogeneous stress state,the simulation results revealed that the strain measurements at different scales (referred to as local,hybrid or global) can provide different volumetric results with moderate to significant deviations from the idealized behavior,and hence different onsets of dilatancy.They also proved that,under low confinement,tensile stresses can take place within the compressed specimen,leading to a great deviation of the dilatancy onset from the idealized behavior.From both experimental and numerical investigations,the difference in sensitivity to the measurement techniques between the deviatoric and the volumetric behaviors is explained by the relatively small values of the volumetric strain.The non-ideal laboratory conditions have more impact on this strain than on the deviatoric one.These findings can have implications for the interpretation of the dilatancy behavior of rock salt,and hence on the geomechanical design aspects in salt formations.

关键词： Rock salt Triaxial tests dilatancy onset End restraint Viscoplasticity

The strength-dilatancy characteristics embraced in hypoplasticity

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Frontiers of Structural and Civil Engineering 2013年第2期7卷 178-187页

作者： Zhongzhi FU Sihong LIU Zijian WANG Geotechnical Engineering Department Nanjing Hydraulic Research InstituteNanjing 210024China College of Water Conservancy and Hydropower Engineering Hohai UniversityNanjing 210098China

The strength-dilatancy characteristics of frictional materials embraced in the hypoplastic model proposed by Gudehus and Bauer are investigated and compared with the revised model suggested by Huang.In the latter the deviatoric stress in the model by Gudehus and Bauer is replaced by a transformed stress according to the stress transformation technique proposed by Matsuoka.The flow rule,the failure state surface equation and the strengthdilatancy relationship embraced in both models are derived analytically.The performance of the two hypoplastic models in reproducing the relationship between the peak strength and the corresponding dilation rate under triaxial compression,plane compression and plane shearing are then extensively investigated and compared with experimental results and with the predictions made by particular classical stress-dilatancy theories.Numerical investigations show that the performance in reproducing the strength-dilatancy relationship is quite satisfactory under triaxial compression stress state in both models and the predictions made by the transformed stress based model are closer to the results obtained from classical stress-dilatancy theories for plane compression and plane shearing problems.

关键词： strength dilatancy hypoplasticity frictional materials

Development and verification of large deformation model considering stiffness deterioration and shear dilation effect in FLAC^(3D)

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International Journal of Mining Science and Technology 2018年第6期28卷 959-967页

作者： Wang Ruijie Li Chong Xu Jinhai Pan Lijin School of Mines China University of Mining and Technology Key Laboratory of Deep Coal Resource Mining (CUMT) Ministry of Education State Key Laboratory of Coal Resources and Safe Mining China University of Mining and Technology

The existing constitutive models of rock with strain softening cannot successfully reflect the damageinduced anisotropy and nonlinearity of the post-peak failure behavior under progressive loading. In order to better reflect the nonlinear stress-strain behavior of rock, especially for the post-peak failure behavior,with expected stiffness degradation and large deformation, a modified constitutive model of rock considering stiffness degradation and dilatation behavior at large deformation was proposed in this study. This study analyzes and discusses various attenuation parameters in the proposed nonlinear plastic constitutive model using FLAC^(3D) software. The excavation-induced stress in rocks was calculated by FLAC^(3D) using the Mohr-Coulomb model, conventional strain model, and the proposed modified model. The obtained results of these models were analyzed and compared with field data. This study shows that the simulated results using the proposed new constitutive model matched much more closely with the measured field data, with an average error less than 5%. This new model can successfully reflect the damage-induced stiffness degradation at large deformation, and can provide a theoretical basis for stability design and evaluation of underground excavation.

关键词： Stiffness degradation dilatancy behavior Nonlinearity Post-peak failure behavior Deep soft rock roadway FLAC^3D

Anisotropic modelling of Opalinus Clay behaviour: From triaxial tests to gallery excavation application

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Journal of Rock Mechanics and Geotechnical Engineering 2017年第3期9卷 53-66页

作者： Francois Bertrand Frédéric Collin Université de Liège Département ArGEnCo/Géomécanique Allée de la découverte 9 4000 Liège Belgium F.R.I.A Fonds de la Recherche Scientifique e FNRS Brussels Belgium

Deep repository in geological formations is the preferential solution considered in many countries to manage high-level nuclear wastes. In Switzerland, the Opalinus Clay is a candidate host rock. In this context, in situ and laboratory tests are conducted on Opalinus Clay to demonstrate the feasibility of deep disposal in this argillaceous formation. This paper presents a constitutive model able to fit the experimental data obtained from some triaxial tests conducted by Jahns(2013) on cores from borehole Schlattingen SLA-1. The elasto-plastic behaviour of Opalinus Clay is reproduced thanks to a DruckerPrager model, taking into account the anisotropy behaviour of this sedimentary rock. The objective is to employ a single set of parameters representative of the material. In a second version of the model, the stress-dependence of the elastic properties and damage are taken into account. Finally, the parameters calibrated with experimental tests are used to simulate the excavation of a gallery with a second gradient approach.

关键词： Opalinus Clay Schlattingen Constitutive modelling Anisotropy dilatancy Localisation Tunnel excavation

A Novel Fractional Plastic Damage Model for Quasi-brittle Materials

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Acta Mechanica Solida Sinica 2021年第5期34卷 706-717页

作者： Peng-Fei Qu Qi-Zhi Zhu Key Laboratory of Ministry of Education for Geomechanics and Embankment Engineering Hohai UniversityNanjing210098China College of Civil and Transportation Engineering Hohai UniversityNanjing210098China

In this work,a novel constitutive model is developed within the framework of fractional plasticity to delineate the coupling between inelastic deformation and damage of quasi-brittle materials.Faced with the common challenge of determining plastic flow direction,we resort herein to the Riemann–Liouville definition of fractional derivatives,instead of introducing an additional plastic potential.The pre-peak hardening behavior is described using an exponential function,while the post-peak softening response is viewed as the consequence of material damage.For describing damage evolution,a damage criterion is constructed in terms of plastic volume dilation related to micro-crack growth.This is conducive to supply a new insight for describing the complex influence of the non-orthogonality of plastic flow on damage evolution.For numerical applications,a semi-implicit return mapping algorithm is proposed.The predictive performance of the model is evaluated by comparing numerical simulations with experimental data under various loading paths.

关键词： Quasi-brittle materials Fractional plasticity Damage dilatancy Numerical algorithm

Critical state shear behavior of the soil-structure interface determined by discrete element modeling

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Particuology 2017年第6期15卷 68-77页

作者： Xiaoqiang Gu Yuanwen Chen Maosong Huang Department of Ceotechnical Engineering Tongii University Shanghai 200092 China Key Laboratory of Ceotechnical and Underground Engineering of the Ministry of Education Shanghai 200092 China

The interface between soil and structure can be referred to as a soil-structure system, and its behavior plays an important role in many geotechnical engineering practices, In this study, results are presented from a series of monotonic direct shear tests performed on a sand-structure interface under constant normal stiffness using the discrete element method （DEM）. Strain localization and dilatancy behavior of the interface is carefully examined at both macroscopic and microscopic scales. The effects of soil initial relative density and normal stress on the interface shear behavior are also investigated, The results show that a shear band progressively develops along the structural surface as shear displacement increases. At large shear displacement a unique relationship between stress ratio and void ratio is reached in the shear band for a certain normal stress, indicating that a critical state exists in the shear band. It is also found that the thickness and void ratio of the shear band at the critical state decreases with increasing normal stress. Comparison of the DEM simulation results with experimental results provides insight into the shear behavior of a sand-structure interface and offers a means for quantitative modeling of such interfaces based on the critical state soil mechanics.

关键词： Discrete element method Interface Direct shear test Shear band dilatancy Critical state

Grain crushing in geoscience materials-Key issues on crushing response,measurement and modeling:Review and preface

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Geoscience Frontiers 2020年第2期11卷 363-374页

作者： Yang Xiao Chandrakant SDesai Ali Daouadji Armin WStuedlein Hanlong Liu Hossam Abuel-Naga Key Laboratory of New Technology for Construction of Cities in Mountain Area Chongqing UniversityChongqing 400045China School of Civil Engineering Chongqing UniversityChongqing 400045China Dept.of Civil Engineering and Engineering Mechanics Univ.of ArizonaTucsonAZ85721USA Universite de Lyon INSA LYONLaboratoire GEOMASJ.C.A.Coulomb34 Avenue des Arts69621VilleurbanneFrance School of Civil and Construction Engineering Oregon State UniversityCorvallisOR97331USA Chongqing University Chongqing 400045China School of Engineering and Mathematical Sciences La Trobe UniversityVictoria3086Australia

Grain crushing is commonly encountered in deep foundation engineering,high rockfill dam engineering,railway engineering,mining engineering,coastal engineering,petroleum engineering,and other geoscience application.Grain crushing is affected by fundamental soil characteristics,such as their mineral strength,grain size and distribution,grain shape,density and specimen size,and also by external factors including stress magnitude and path,loading rate and duration,degree of saturation,temperature and geochemical environment.Crushable material becomes a series of different materials with the change in its grading during grain crushing,resulting in a decrease in strength and dilatancy and an increase in compressibility.Effects of grain crushing on strength,dilatancy,deformation and failure mechanisms have been extensively investigated through laboratory testing,discrete element method(DEM)modelling,Weibull statistics,and constitutive modelling within the framework of the extended crushing-dependent critical state theory or the energy-based theory.Eleven papers summarized in this review article for this special issue addressed the above issues in grain crushing through the advanced testing and modelling.

关键词： Grain crushing Particle breakage Strength dilatancy DEM modelling Constitutive modelling

Spatial correlation-based characterization of acoustic emission signal-cloud in a granite sample by a cube clustering approach

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International Journal of Mining Science and Technology 2021年第4期31卷 535-551页

作者： Dongjie Xue Zepeng Zhang Cheng Chen Jie Zhou Lan Lu Xiaotong Sun Yintong Liu School of Mechanics and Civil Engineering China University of Mining and Technology-BeijingBeijing 100083China State Key Laboratory of Coal Mine Disaster Dynamics and Control Chongqing UniversityChongqing 400030China State Key Laboratory of Coal Resource and Safe Mining China University of Mining and Technology-BeijingBeijing 100083China

To extract more in-depth information of acoustic emission(AE)signal-cloud in rock failure under triaxial compression,the spatial correlation of scattering AE events in a granite sample is effectively described by the cube-cluster model.First,the complete connection of the fracture network is regarded as a critical state.Then,according to the Hoshen-Kopelman(HK)algorithm,the real-time estimation of fracture con-nection is effectively made and a dichotomy between cube size and pore fraction is suggested to solve such a challenge of the one-to-one match between complete connection and cluster size.After,the 3D cube clusters are decomposed into orthogonal layer clusters,which are then transformed into the ellip-soid models.Correspondingly,the anisotropy evolution of fracture network could be visualized by three orthogonal ellipsoids and quantitatively described by aspect ratio.Besides,the other three quantities of centroid axis length,porosity,and fracture angle are analyzed to evaluate the evolution of cube cluster.The result shows the sample dilatancy is strongly correlated to four quantities of aspect ratio,centroid axis length,and porosity as well as fracture angle.Besides,the cube cluster model shows a potential pos-sibility to predict the evolution of fracture angle.So,the cube cluster model provides an in-depth view of spatial correlation to describe the AE signal-cloud.

关键词： Acoustic emission Triaxial compression Fracture connection Spatial correlation Cube cluster model dilatancy

Shear strength of extremely altered serpentinites based on degree of saturation(Ankara, Turkey)

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Journal of Mountain Science 2019年第4期16卷 944-954页

作者： Koray ULAMI? Department of Geological Engineering Ankara University

The term "mélange" has several definitions due to the origin, tectonic and petrographical features. The geotechnical engineering behaviors of mélanges are either dominated by different kinds of intact rock blocks or matrix material. Landslides were encountered within the serpentinite matrix of Ankara Mélange, which is a typical bimrock mass. The residual sections of the extremely altered serpentinites are sandy soils. Such soils undergo rapid change of saturation, leading to shear strength reduction. Undisturbed and disturbed samples were obtained from the outcrops for shear box tests. Geochemical and petrographical composition of the serpentinites were determined by XRF(X Ray Fluorescence), XRD(X-ray diffraction) and thin section inspections, in order to outline the alteration process. Based on field observations, physically decomposed core stones exist beneath 40-120 cm thick residual green and grey-dark grey residual sandy soil. Physical and mechanical properties of the soils were tested with particular emphasis on residual shear strength parameters. Disturbed samples were remolded by standard compaction. The field work was completed during both rainy and summer seasons. Disturbed samples were prepared using phase diagrams in order to attain varying saturation degree. Two distinct sandy soil groups were determined through classification tests. The volumetric compression and/or expansion of the loose and dense samples were also considered based on the angle of dilatancy. A series of consolidated and drained shear box tests were conducted with ascending degree of saturation. The reduction of effective apparent cohesion, internal friction angle and dilatancy angle were determined to obtain a threshold of the degree of saturation. All the sand samples had zero residual internal friction angle and/or apparent cohesion after reaching 70% degree of saturation.

关键词： Mélange Serpentinite Shear strength Saturation dilatancy Ankara