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Numerical Analysis of a Tunnel Subjected to Blast Loads in a Transversely Isotropic Rock Mass

INTERNATIONAL JOURNAL OF GEOMECHANICS 2024年第10期24卷

作者： Deshpande, Venkatesh M. Chakraborty, Tanusree Indian Inst Technol IIT Delhi Dept Civil Engn New Delhi 110016 India

The present study investigates the stability of a tunnel subjected to blast loads. The tunnel is placed in a transversely isotropic rock mass. Numerical simulations are performed using the discrete-element method. The rock material between the bedding planes/joints is discretized as Voronoi polygons. The research focuses on the significance of discretizing the rock material between the bedding planes as Voronoi polygons for studying a tunnel's stability under blast loads. To this end, the influence of Voronoi polygon size, joint spacing, anisotropy angle, cover depth, and earth pressure coefficient on the tunnel response are examined. The tunnel response is measured in terms of normalized crown displacement. The study provides many novel insights that can be used to improve the design of rock tunnels. It is found that it is vital to discretize rock grains as Voronoi blocks for studying the tunnel response. When Voronoi blocks are considered, the tunnel stability increases for anisotropy angles 30 degrees and 60 degrees but decreases for angles 0 degrees and 90 degrees when no Voronoi blocks are used. The tunnel becomes more vulnerable to damage as the Voronoi block size increases. It is noted that the joint spacing and Voronoi block size are interlinked, and their influence must be considered together for assessing the tunnel stability. When joint spacing is kept twice or more than the Voronoi size, the crown displacement is higher than when joint spacing is equal to or closer to the Voronoi size. It is observed that the crown displacement is maximum when the earth pressure coefficient equals 2. Therefore, the influence of change in the earth pressure coefficient is considered the most severe of all the parameters studied.

关键词： Tunnel stability Blast load discrete-element method Voronoi polygons Dip angle Joint spacing

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Micromechanics of Hydro-Thermo-Mechanical Processes in Rock Accounting for Thermal Convection

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JOURNAL OF ENGINEERING MECHANICS 2019年第8期145卷

作者： Tomac, Ingrid Gutierrez, Marte Univ Calif San Diego Dept Struct Engn 9500 Gilman Dr La Jolla CA 92093 USA Colorado Sch Mines Dept Civil & Environm Engn 1012 14th St Golden CO 80401 USA

This paper presents the results of a comprehensive micromechanical study to improve the understanding of the coupled hydro-thermo-mechanical (HTM) processes during injection of pressurized cold fluid in permeable hot rock. At the microscopic level, it is expected that fluid flow-induced convective temperature changes in the voids will dominate the conductive heat flow from grain to grain. However, the coupled interactions between fluid flow, thermal convection, and conduction, and the resulting changes in local permeability due to thermo-poroelastic stresses at the grain scale remain poorly understood. Moreover, almost all previous studies at a large scale have focused only on thermal conduction. This study used the discrete-element method (DEM) modified to account for convective heat transport to model the particulate interactions between rock grains and between rock deformation, fluid pressure, and temperature. The results indicate that wellbore pressure, provided it is less than the fracturing threshold, has a less significant role in rock cooling around the wellbore, which is governed predominately by rock permeability, as previously thought. Different applied flow rates into the wellbore resulted in low and high wellbore pressures at short times in the absence of rock fracturing. As expected, convective heat transport dominated over conduction, resulting in a cooled ring around the wellbore without a significant thermal gradient zone due to conductive heat flow. As the fluid infiltrates and cools the rock, preferential fluid flow paths occur as fingering instabilities that are oriented toward the minimum principal horizontal stress even in the absence of initial local anisotropic porosity variations.

关键词： discrete-element method Convective-conductive heat flow Hot dry rock Rock permeability Wellbore pressure

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Microstructural Investigation of Soil Suction and Hysteresis of Fine-Grained Soils

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JOURNAL OF GEOTECHNICAL AND GEOENVIRONMENTAL ENGINEERING 2012年第1期138卷 38-46页

作者： Anandarajah, A. Amarasinghe, Priyanthi M. Johns Hopkins Univ Dept Civil Engn Baltimore MD 21218 USA

The relationship between soil suction and degree of water saturation (also known as the soil-water characteristic curve or SWCC) for a given soil depends on a number of variables such as the soil type, mineral type, fluid type, pore size distribution, and anisotropy. In addition, the SWCC is found to exhibit a form of hysteresis, in that it is different in wetting and drying. Design of structures founded on unsaturated soils requires an in-depth microscopic understanding of the variables controlling SWCC and the underlying hysteresis. Most of the past basic studies have focused on granular materials, with solid particles represented by spheres. The present study is focused on clayey soils involving platelike solids. The analysis method of molecular dynamics (MD) is used to understand the nature of clay-water capillary meniscus. On the basis of the observations from the MD analysis and the Young-Laplace equation, a model is proposed for predicting SWCC and the associated hysteresis. The microscopic parameters needed for the model are obtained by analyzing the fabric of numerical specimens prepared by the discrete-element method (DEM) of analysis of an assembly of clay particles. The results are shown to be consistent with experimental observations. DOI: 10.1061/(ASCE)GT.1943-5606.0000555. (C) 2012 American Society of Civil Engineers.

关键词： Montmorillonite Kaolinite Molecular dynamics discrete-element method SWCC Soil suction Inkbottle effect Contact angle Surface tension

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Microscale Descriptors for Particle-Void Distribution and Jamming Transition in Pre- and Post-Liquefaction of Granular Soils

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JOURNAL OF ENGINEERING MECHANICS 2018年第8期144卷 1-11页

作者： Wei, Jiangtao Huang, Duruo Wang, Gang Hong Kong Univ Sci & Technol Dept Civil & Environm Engn Kowloon Hong Kong Peoples R China Tsinghua Univ Dept Hydraul Engn Beijing 100084 Peoples R China

Micromechanical modeling provides significant insight into the fundamental mechanism of soil liquefaction. In this study, a series of undrained cyclic simple shear simulations were conducted by using discrete element method (DEM). The particle-scale information provided by DEM was used to quantify the local void distribution around particles. Two microscale descriptors, named as the shape-elongation descriptor (Ed) and the orientation-anisotropy descriptor (Ad), were proposed to quantify the overall anisotropy of local void distribution in the granular packing. Before initial liquefaction, the particle-void distribution remains to be globally isotropic for isotropically consolidated samples. An irreversible development of anisotropy in terms of Ed and Ad mainly occurs in the post-liquefaction stage. In addition, jamming transition of the liquefied soil is determined by using these descriptors because a unique hardening state line (HSL) is found in the Ed-Ad space that can differentiate a post-liquefaction flow state from a hardening or jamming state. Furthermore, large post-liquefaction flow strains are found to be closely correlated to the descriptors.

关键词： discrete-element method Liquefaction Particle-void structure Jamming transition

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discrete and Continuum Numerical Modeling of Soil Arching between Piles

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INTERNATIONAL JOURNAL OF GEOMECHANICS 2019年第2期19卷 4018195.1-4018195.13页

作者： Quoc Anh Tran Villard, Pascal Dias, Daniel Aalto Univ Dept Civil Engn FI-02150 Espoo Finland Univ Grenoble Alpes CNRS Grenoble INP 3SR F-38000 Grenoble France

The aim of this study was to investigate the soil-arching phenomenon between piles by adopting two different numerical methods: the discrete-element method and the finite-difference method. The discrete-element method, in which soil is represented by an assembly of particles of various shapes that interact with friction at contact points, allows analysis of the phenomenon at the microscopic level. The discrete-element method naturally captures the mechanical behavior of frictional materials. In contrast, the finite-difference method examines the problem at the macroscopic level. Specifically, soils are considered homogeneous materials from the macroscopic viewpoint. In the continuum approach, an appropriate constitutive model that considers the shear-resistance degradation is used to capture the evolution of frictional materials as obtained by using the discrete approach. The numerical microparameters and macroparameters for the two numerical models were calibrated from triaxial test simulations. A comparison of these two approaches for the case of a soft soil improved by vertical piles was conducted. The study highlights the limitations and advantages of each method with respect to the soil-arching investigation.

关键词： discrete-element method Finite-difference method Soil arching Piled embankment Granular soil Softening behavior

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Flow-Structure Interaction Mechanism under Coriolis Conditions

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JOURNAL OF ENGINEERING MECHANICS 2021年第4期147卷 04021015-04021015页

作者： Zhang, Bei Huang, Yu Zhu, Chongqiang Tongji Univ Dept Geotech Engn Coll Civil Engn Shanghai 200092 Peoples R China Tongji Univ Key Lab Geotech & Underground Engn Minist Educ Shanghai 200092 Peoples R China

The Coriolis effect in centrifuge modeling of flow-structure interaction has not been well understood, and thus this paper presents numerical simulations to address this issue. The results indicate that the Coriolis acceleration obviously regulated the flow-structure interaction pattern. The maximum total impact force was amplified by approximately 2 times, and the force was distributed along the entire barrier surface when changing the Coriolis acceleration direction from acting at the slope to acting away from the slope. Reducing the flow velocity by 30%-40% decreased the amplification ratio by approximately 14%-29%. The alteration of the microcontact condition and the energy consumption of the dry granular flow was the main influence mechanism of the Coriolis acceleration on the flow's impact behavior. The influence of the Coriolis effect on the viscous flow impact was completely different from that exerted on frictional flows. This discrepancy resulted from the intrinsic flow mobility determined by the material characteristics. Some practical discussions about centrifuge modeling of flow-structure interaction are made as well as some suggestions for future work.

关键词： Flow-structure interaction Coriolis effect Geotechnical centrifuge Flow impact patterns discrete-element method

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Particle Breakage Effect on Compression Behavior of Realistic Granular Assembly

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INTERNATIONAL JOURNAL OF GEOMECHANICS 2021年第7期21卷 04021105-04021105页

作者： Zhang, Tao Yang, Weihao Zhang, Chi Hu, Chenchen China Univ Min & Technol State Key Lab Geomech & Deep Underground Engn Xuzhou 221116 Jiangsu Peoples R China

A numerical investigation of the effect of particle breakage on the one-dimensional compression behavior of a realistic granular assembly was carried out using the discrete-element method. The morphologies of sands were obtained using X-ray microcomputed tomography. Sand assemblies were generated in terms of the statistical distribution of sphericity from real sands. The results of single-particle compression tests showed that particle shape significantly affects crushing strength. Particle breakage had a significant influence on compressive deformation, as demonstrated by comparing breakable assemblies with unbreakable ones. The strong force distribution became broader, and the proportion of weak force increased with particle breakability. Looser samples underwent much more particle breakage than did denser samples. It was found that breakage dissipation was a small fraction of energy input compared with frictional dissipation. An excellent hyperbolic relationship between relative breakage and energy input was found, which was independent of initial void ratio.

关键词： One-dimensional compression Particle breakage Realistic particle shape discrete-element method

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Study on the Anisotropic Shear Strength of Rough Joint via 3D Scanning, 3D Printing, and 3D discrete-element Modeling

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INTERNATIONAL JOURNAL OF GEOMECHANICS 2022年第6期22卷 04022058-04022058页

作者： Du, Yaohui Bao, Han Yin, Peijie Liu, Changqing He, Zhi Xu, Xunhui Lanzhou Jiaotong Univ Sch Civil Engn Lanzhou 730070 Peoples R China Changan Univ Sch Highway Xian 710064 Peoples R China

The anisotropic shear strength of rough joints is examined from both experiments and numerical simulations in this paper. The rough joints in the experiment are prepared by combining 3D laser scanning and 3D printing technology. The direct shear tests are conducted in eight shear directions under constant normal load condition (CNL) with the normal stress of 0.2, 0.5, and 1.0 MPa. The dramatic variation of shear strength in different shear directions is observed from experimental results. Meanwhile, the numerical simulation based on the three-dimensional discrete-element method (DEM) is conducted, in which, the method to generate the identical rough joint by connecting triangular walls is proposed. With the calibrated microparameters from the unconfined compression test and direct shear test, the anisotropic shear strength is also observed in the numerical simulation, which is consistent with the experimental result. Accordingly, the topography anisotropy of the rough surface is analyzed, and the statistical parameter, Z(2)(theta), is found closely related to the anisotropic shear strength of rough joints. Based on this, the Barton model is modified to estimate the shear strength of artificial joints with an anisotropic effect involved. (C) 2022 American Society of Civil Engineers.

关键词： Anisotropy Shear strength Rough joint discrete-element method

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Improved Electrodynamic Particle-Size Sorting System for Lunar Regolith

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JOURNAL OF AEROSPACE ENGINEERING 2022年第1期35卷 04021115-04021115页

作者： Kawamoto, Hiroyuki Morooka, Hirofumi Nozaki, Hiroyuki Waseda Univ Res Inst Sci & Engn Shinjuku Ku 17 Kikuicho Tokyo 1620044 Japan Waseda Univ Dept Appl Mech & Aerosp Engn Shinjuku Ku 3-4-1 Okubo Tokyo 1698555 Japan

In situ resource utilization (ISRU) of lunar regolith is indispensable for the success of large-scale and long-term human lunar explosions at lower costs. Many new technologies must be developed to realize efficient ISRU. Because particle sorting is one of the essential processes of ISRU, a unique technology has been developed using the balance between electrodynamic and gravitational forces. First, a sorting system using an electrodynamic standing wave was developed. The particles on the parallel-line electrodes were agitated by the electrodynamic force created by the application of a standing wave, and floated small particles at a high altitude were collected in a box located above the electrodes. The experiment and numerical calculation indicated that although a high collecting position was preferable for sorting small particles, a large number of small particles hardly reached a high position and a high yield was not attained. Next, an improved sorting system that uses a traveling wave instead of a standing wave was developed to mitigate the incompatibility. When a four-phase high voltage is applied to the vertically supported parallel-line electrodes, an electrodynamic traveling wave is formed above the electrodes, forcing small regolith particles to move upward at a high position, while large particles are apt to fall. Additionally, particles were fed through a vibrating sieve to break off the aggregated particles. Finally, an averaged particle size of 12 mu m and 30% in a yield of particles less than 10 mu m particles was attained. The system would be suitable for space applications because it is simple, lightweight, has low power consumption, and does not require any mechanical drive or consumables. (C) 2021 American Society of Civil Engineers.

关键词： In situ resource utilization (ISRU) Lunar exploration Regolith Electrostatics discrete-element method Particle sorting Traveling wave

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discrete-element Analysis of Influence of Granular Soil Density on Earthquake Surface Fault Rupture Interaction with Rigid Foundations

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JOURNAL OF GEOTECHNICAL AND GEOENVIRONMENTAL ENGINEERING 2019年第11期145卷

作者： Garcia, Fernando E. Bray, Jonathan D. Univ Calif Berkeley Dept Civil & Environm Engn Berkeley CA 94702 USA

Parametric analysis of the effects of soil relative density on earthquake surface fault rupture interaction with foundations having different contact pressures and positions was performed with the discrete-element method (DEM). DEM simulations provide insights into particle responses not possible with continuum methods. The relative density of soil has a significant impact on the interaction of surface fault rupture with a building foundation. The number of horizontally oriented contacts achieves a peak value before decreasing during reverse fault rupture through a dense particle assemblage due to its strain-softening response, and the number of horizontally oriented contacts tends to monotonically approach a constant value during reverse fault rupture through a loose particle assemblage. The mobilization of stresses reflects the trends seen with the contact forces and shows quantitatively the more brittle response of denser particle assemblages. Heavy foundations consistently alter the path of reverse fault rupture propagation while undergoing less rotation than light foundations. During normal fault rupture, heavy foundations can undergo more rotation when positioned on the footwall side of the free-field surface outcrop location.

关键词： discrete-element method Earthquake fault rupture High-performance computing Relative density Soil-foundation interaction

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