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Ultrasonic imaging of microscale processes in quartz gouge during compression and shearing

Journal of Rock Mechanics and Geotechnical Engineering 2020年第6期12卷 1137-1151页

作者： Amin Gheibi ahmadreza hedayat Colorado School of Mines GoldenUSA

Active ultrasonic monitoring in rock joints and gouge materials has the potential to detect the signatures of shear failure for a wide range of sliding modes,from slow and stable movements to fast and unstable *** these collected measurements currently are being used to identify the seismic precursors to shear failure in rock joints and gouge materials,the underlying physical processes and contact scale mechanisms that control the changes in ultrasonic wave attributes are still poorly *** address this knowledge gap,this paper aims to investigate the relationship between the variations in ultrasonic wave attributes and the underlying particle scale mechanisms during both compression and *** double direct shear experiments were coupled with ultrasonic wave propagation measurements on granular quartz gouges,in which the gouge layers were sheared under different sliding velocities and constant normal stress ***,ultrasonic waveforms were continuously recorded during shearing with a fast data acquisition system and three pairs of ultrasonic wave transducers embedded at the two sides of the gouge *** particle comminution mechanisms were observed from the non-uniform distribution of normal and shear stresses through the changes in ultrasonic transmissivity and scanning electron microscope(SEM)*** results show that the signatures of the geometry-and time-dependent variations of the inter-particle contact quality and pore volume changes with sliding velocity and slip accumulation were clearly captured from the variations in the transmitted wave amplitude and the dominant frequency,*** addition,we found that variations in dominant frequency corresponded to dilation and compaction of the granular gouge layer during compression as well as stable and unstable *** results therefore confirmed that nondestructive acoustic techniques are capable of capturing a variety of micromechanical process

关键词： Granular material Ultrasonic investigation Particle comminution Compaction and dilation

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Physical model simulation of rock-support interaction for the tunnel in squeezing ground

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Journal of Rock Mechanics and Geotechnical Engineering 2022年第1期14卷 82-92页

作者： Ketan Arora Marte Gutierrez ahmadreza hedayat Civil and Environmental Engineering Colorado School of MinesGoldenCO80401USA

The existence of squeezing ground conditions can lead to significant challenges in designing an adequate support system for *** empirical,observational and analytical methods have been suggested over the years to design support systems in squeezing ground conditions,but all of them have some *** this study,a novel experimental setup having physical model for simulating the tunnel boring machine(TBM)excavation and support installation process in squeezing clay-rich rocks is *** observations are made to understand better the interaction between the support and the squeezing *** physical model included a large true-triaxial cell,a miniature TBM,laboratoryprepared synthetic test specimen with properties similar to natural mudstone,and an instrumented cylindrical aluminum support *** were conducted at realistic in situ stress levels to study the time-dependent three-dimensional tunnel support *** tunnel was excavated using the miniature TBM in the cubical rock specimen loaded in the true-triaxial cell,after which the support was *** confining stress was then increased in stages to values greater than the rock’s unconfined compressive strength.A model for the time-dependent longitudinal displacement profile(LDP)for the supported tunnel was proposed using the tunnel convergence measurements at different times and stress *** LDP formulation was then compared with the unsupported model to calculate the squeezing amount carried by the *** increase in thrust in the support was backcalculated from an analytical solution with the assumption of linear elastic *** on the test results and case studies,a recommendation to optimize the support requirement for tunnels in squeezing ground is proposed.

关键词： Squeezing ground Tunnel support system Longitudinal displacement profile Rock-support interaction

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Tunnels in squeezing clay-rich rocks

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Underground Space 2021年第4期6卷 432-445页

作者： Ketan Arora Marte Gutierrez ahmadreza hedayat Caichu Xia Civil and Environmental Engineering Colorado School of MinesGoldenCO 80401USA Geotechnical Engineering Tongji UniversityShanghai 200092China

Squeezing ground conditions,which can lead to severe loads in tunnels,have historically been associated with the presence of clay minerals in the *** the years,many methodologies have been proposed to predict squeezing in tunnels based on tunnel depth,in situ stress,ground mineralogy,and ground strength and deformation *** paper presents a comprehensive review of methodologies to predict tunnel squeezing in clay-rich rocks.A new methodology is proposed where ground conditions and squeezing potential are assessed based on the Stress History and Normalized Soil Engineering Properties(SHANSEP)approach adapted to clayrich rocks,Peck’s stability number and Hoek&Brown’s(1997)Geological Strength Index(GSI).A squeezing number S is suggested to classify ground conditions based on the level of squeezing that the ground may experience in response to ***,it is demonstrated that by combining the proposed classification system and an existing classification system for ground squeezing condition,an accurate estimate of tunnel strain can also be *** proposed method is applied to four case studies of tunnels in squeezing ground in shale and mudstone.

关键词： Squeezing ground High in situ stress Critical strain Clay-rich rocks Mudrock Shale Tunnels

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Experimental and Numerical Study of Shear Fracture in Brittle Materials with Interference of Initial Double Cracks

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Acta Mechanica Solida Sinica 2016年第5期29卷 555-566页

作者： Hadi Haeri Vahab Sarfarazi Mohammad Fatehi Marji ahmadreza hedayat Zheming Zhu Young Researchers and Elite Club Bafgh BranchIslamic Azad UniversityBafghIran Department of Mining Engineering Hamedan University of TechnologytiamedanIran Associate Prof. Head of Mine Exploitation Engineering DepartmentFaculty of Mining and MetallurgyInstitution of EngineeringYazd UniversityYazdIvan Department of Civil and Environmental Engineering Colorado School of MinesGoldenColorado 80401USA College of Architecture and Environment Sichuan UniversityChengdu 610065China

A simultaneous experimental and numerical study of shear fracture of concrete-like materials is carried out using Brazilian disc specimens with initial double edge cracks and fourpoint bending beam specimens with double *** interference effects of two cracks/notches are investigated through varied ligament angles and crack *** is shown that shear fracturing paths change remarkably with the initial ligament angles and crack *** cracked specimens are numerically simulated by an indirect boundary element method.A comparison between the numerical results and the experimental ones shows good agreement.

关键词： cracked Fracture overlapped fracturing ligament simultaneous discontinuity cracking specimen shrinkage

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Isotropic compression behavior of granular assembly with non-spherical particles by X-ray micro-computed tomography and discrete element modeling

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Journal of Rock Mechanics and Geotechnical Engineering 2021年第5期13卷 972-984页

作者： Nan Zhang ahmadreza hedayat Shaoyang Han Runlin Yang Héctor Gelber Bolaños Sosa Juan JoséGonzález Cárdenas Guido Edgard SalasÁlvarez Department of Civil and Environmental Engineering Colorado School of Mines1500 Illinois St.GoldenCO80401USA Key Laboratory of Ministry of Education for Geomechanics and Embankment Engineering Hohai UniversityNanjing210098China School of Civil and Resource Engineering University of Science and Technology BeijingBeijing100083China Universidad Nacional de San Agustín de Arequipa ArequipaPeru

The particle morphological properties,such as sphericity,concavity and convexity,of a granular assembly significantly affect its macroscopic and microscopic compressive behaviors under isotropic loading ***,limited studies on investigating the microscopic behavior of the granular assembly with real particle shapes under isotropic compression were *** this study,X-ray computed tomography(mCT)and discrete element modeling(DEM)were utilized to investigate isotropic compression behavior of the granular assembly with regard to the particle morphological properties,such as particle sphericity,concavity and interparticle *** mCT was first used to extract the particle morphological parameters and then the DEM was utilized to numerically investigate the influences of the particle morphological properties on the isotropic compression *** image reconstruction from mCT images indicated that the presented particle quantification algorithm was robust,and the presented microscopic analysis via the DEM simulation demonstrated that the particle surface concavity significantly affected the isotropic compression *** observations of the particle connectivity and local void ratio distribution also provided insights into the granular assembly under isotropic *** found that the particle concavity and interparticle friction influenced the most of the isotropic compression behavior of the granular assemblies.

关键词： X-ray computed tomography(mCT) Discrete element modeling(DEM) Isotropic compression Particle surface curvature Particle morphology

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