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Progressive evolution and failure behavior of a Holocene river-damming landslide in the SE Tibetan Plateau, China

LANDSLIDES 2022年第5期19卷 1069-1086页

作者： Li, Yanyan Feng, Xuyang Yao, Aijun Zhang, Zhihong Li, Kun Wang, Qiusheng Song, Shengyuan Beijing Univ Technol Fac Urban Construct Beijing 100124 Peoples R China Minist Water Resources Gen Inst Water Resources & Hydropower Planning & Beijing 100120 Peoples R China Jilin Univ Coll Construct Engn Changchun 130026 Peoples R China

This paper presents a study on an ancient river-damming landslide in the SE Tibet Plateau, China, with a focus on time-dependent gravitational creep leading to slope failure associated with progressive fragmentation during motion. Field investigation shows that the landslide, with an estimated volume of 4.9 x 10(7) m(3), is a translational toe buckling slide. Outcrops of landslide deposits, buckling, toe shear, residual landslide dam, and lacustrine sediments are distributed at the slope base. The landslide deposits formed a landslide dam over 60 m high and at one time blocked the Jinsha River. Optically stimulated luminescence dating for the lacustrine sediments indicates that the landslide occurred at least 2,600 years ago. To investigate the progressive evolution and failure behavior of the landslide, numerical simulations using the distinct element method are conducted. The results show that the evolution of the landslide could be divided into three stages: a time-dependent gravitational creep process, rapid failure, and granular flow deposition. It probably began as a long-term gravitationally induced buckling of amphibolite rock slabs along a weak interlayer composed of mica schist which was followed by progressive fragmentation during flow-like motion, evolving into a flow-like movement, which deposited sediments in the river valley. According to numerical modeling results, the rapid failure stage lasted 35 s from the onset of sudden failure to final deposition, with an estimated maximum movement rate of 26.8 m/s. The simulated topography is close to the post-landslide topography. Based on field investigation and numerical simulation, it can be found that the mica schist interlayer and bedding planes are responsible for the slope instability, while strong toe erosion caused by the Jinsha River caused the layered rock mass to buckle intensively. Rainfall or an earthquake cannot be ruled out as a potential trigger of the landslide, considering the climate condi

关键词： Tibetan Plateau Buckling Landslide evolution distinct element method Creep Voronoi

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Multi-scale pullout behaviour of strip anchor plates embedded in marine hydrate bearing sediments

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COMPUTERS AND GEOTECHNICS 2022年 141卷 104472-104472页

作者： Du, Yukun Liu, Fang Zhou, Mingliang He, Jie Tongji Univ State Key Lab Disaster Reduct Civil Engn 1239 Siping Rd Shanghai 200092 Peoples R China Tongji Univ Key Lab Geotech & Underground Engn Minist Educ 1239 Siping Rd Shanghai 200092 Peoples R China Tongji Univ Dept Geotech Engn 1239 Siping Rd Shanghai 200092 Peoples R China

Anchor plates are widely used in offshore platform infrastructure due to their great pullout bearing capacity. With the increasing extraction activities of oil and gas resources in sub-marine environments, strip anchor plates are likely to be embedded inside existing hydrate bearing sediments, which will inevitably change its pullout behaviour and bring hidden safety risks to the infrastructure. This paper establishes both DEM models and FEM models of the interaction between a strip anchor plate and the marine hydrate bearing sediments. The mechanical responses of the strip anchor plate subjected to vertical pullout loads are investigated under the conditions of different hydrate saturations and embedded depths. The failure modes obtained by both numerical methods are analyzed and discussed from both the macro and micro perspectives. The results show that the presence of hydrate significantly improves the pullout bearing capacity of the strip anchor plate. In the DEM simulations, the hydrate bearing sediment presents a brittle failure and develops shear bands which extend from both side-edges of the anchor plate to the ground. In the FEM simulations, hydrate bearing sediments are controlled by the ductile failure mode. The angle between the shear band and the vertical direction in the hydrate bearing sediment is controlled by the friction angle of the sediment.

关键词： Hydrate bearing sediments Pullout behaviours Anchor plates Failure modes Finite element method distinct element method

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DEM-Based Study on the Mechanical Behaviors of Pore-Filling MHBS under Drained True Triaxial Conditions Varying the Intermediate Stress Ratio of Constant Mean Effective Stresses

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INTERNATIONAL JOURNAL OF GEOMECHANICS 2022年第9期22卷 04022132-04022132页

作者： He, Jie Zhu, Hehua Zhou, Mingliang Tongji Univ Coll Civil Engn Shanghai 200092 Peoples R China Tongji Univ State Key Lab Disaster Reduct Civil Engn Shanghai 200092 Peoples R China Tongji Univ Minist Educ Key Lab Geotech & Underground Engn Shanghai 200092 Peoples R China Tongji Univ Dept Geotech Engn Shanghai 200092 Peoples R China

Methane hydrate-bearing soils (MHBS) are natural soil deposits that contain methane hydrate (MH) in the pores and have attracted a huge amount of attention as alternative energy to study mechanical properties for realizing large-scale commercial extraction. Especially, MHBS respond to applied loads under complex stress conditions, that is, the effect of the intermediate stress ratio on mechanical characteristics of MHBS. The effect of different values of intermediate stress ratios on the geomechanical responses of pore-filling MHBS was analyzed using the distinct element method (DEM). MH clusters are cemented together as agglomerates of spheres, which fill into the voids of the soil specimen according to the MH saturation. Then, the numerical pore-filling MHBS experimented with different loading paths of the true triaxial tests. Finally, the effects of the intermediate stress ratio on the mechanical characteristics of pore-filling MHBS were analyzed from two aspects, that is, macromechanical responses and micromechanical responses. The results showed that there were correlation analyses between the variations in the strong fabric and principal stresses. The friction angle increased with the intermediate stress ratio until it reached a peak value, and decreased thereafter. The Lade-Duncan criterion is approximately suitable to describe the three-dimensional strength of MHBS.

关键词： distinct element method Pore-filling methane hydrate-bearing sediments Intermediate stress ratio True triaxial tests Mechanical response

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Investigation of the mechanical and shrinkage properties of plastic-rubber compound modified cement mortar with recycled tire steel fiber

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CONSTRUCTION AND BUILDING MATERIALS 2022年 334卷

作者： Su, Peifeng Dai, Qingli Li, Miaomiao Ma, Yunxiang Wang, Jiaqing Michigan Technol Univ Dept Civil Environm & Geospatial Engn E Lansing MI 48824 USA Nanjing Forestry Univ Coll Civil Engn Nanjing Peoples R China

To facilitate the recycling of waste solids in cement-based materials, plastic-rubber (PR) compound modified mortar (PRM) samples and recycled steel fiber (RSF)-reinforced plastic-rubber modified mortar (PRSRM) samples were prepared and tested to evaluate their mechanical and drying shrinkage properties. PR compound particles, with a mesh size of #8, replaced the natural aggregates with four volume percentages: 2%, 5%, 7.5%, and 10%. The fiber was added with a constant volume fraction of 0.2%. Accordingly, control mortar, PRM mortar with different PR replacement ratios, and PRSRM mortar with RSF were prepared and tested. A numerical splitting tension test model was also established based on the two-dimensional distinct element method (DEM) to investigate the crack initiation and propagation mechanism of the PRM samples. The mechanical test results indicated that the addition of RSF enlarged the compressive strength by 14-27% PRM samples. Meanwhile, both PR and RSF improved mortar flexural behavior by increasing the fracture energy. The SEM image of a fracture surface and DEM simulation showed the crack propagation path was changed by PR particles due to its lower stiffness. Meanwhile, the 7-days drying shrinkage length change was reduced by about 25% due to the PR's porous structure and water-retaining ability. Overall, the sustainable material design with the combination of PR and RSF would promote the full-recycling of waste tires in cement-based materials.

关键词： Cement mortar Plastic-rubber compound Recycled steel fiber Mechanical properties Drying shrinkage distinct element method Crack propagation

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Three Dimensional Modeling of a Multiblock Roman Column Under Harmonic Excitations 4th

Three Dimensional Modeling of a Multiblock Roman Column Unde...

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International Conference on Protection of Historical Constructions (PROHITECH)

作者： Tabbara, Mazen Karam, Gebran Beaino, Charbel Jello, Josiane Lebanese Amer Univ Dept Civil Engn Byblos Lebanon

ISBN: (纸本)9783030907884;9783030907877

A three dimensionalDEMmodelwas developed for a single multiblock Corinthian column from the Roman temple of Jupiter in Baalbek and used to investigate the response of the full size column as well as 0.5 m and 1 m reduced models that are used in shaking table experiments. 25 cycles of harmonic pulses of varying periods and accelerations were applied until collapse was observed. The critical combinations causing collapse were identified. The displacement history of the top column block was plotted alongside the harmonic excitation signal applied to the base of the column in order to visualize the rocking and/or wobbling response. The in-plane rocking and the out-of-plane wobbling were identified. Numerical stability charts were plotted showing safe-unsafe boundaries. Column responses included stable and unstable rocking of the whole column, stable and unstable multi-block rocking with toppling of upper blocks and combinations of rocking and wobbling. The type of column response, resulting structural disorder and collapse modes are shown to be dependent on the excitation period. The reliability of the results and the predictive capabilities of the model are discussed.

关键词： Rocking Overturning Wobbling Harmonic excitation distinct element method Multiblock column

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A distinct element method for large scale simulations of carbon nanotube assemblies

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JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS 2013年第3期61卷 762-782页

作者： Ostanin, Igor Ballarini, Roberto Potyondy, David Dumitrica, Traian Univ Minnesota Dept Civil Engn Minneapolis MN 55455 USA Itasca Consulting Grp Inc Minneapolis MN 55401 USA Univ Minnesota Dept Mech Engn Minneapolis MN 55455 USA

Mesoscale simulation techniques are becoming increasingly important due to the interest in complex mechanical problems involving nanomaterials. We propose applying the established macroscopic modeling concept of distinct spherical elements down to the mesoscale to simulate mechanical behavior of carbon nanotube systems. Starting from a microscopic description, the important interactions are encapsulated into two types of contact models that act simultaneously. Each individual nanotube is coarse-grained into a chain of spherical elements interacting by parallel-bonded contacts, representing the short-ranged covalent bonding. An anisotropic van der Waals model with aligning moments acts at the contact between elements located in different tubes to represent the long-ranged interactions. The promising potential of the proposed methodology to model large scale carbon nanotube assemblies is illustrated with several examples, including self-folding of individual nanotubes, mechanical testing of nanotube ropes, self-assembly of a high-porosity nanotube paper, and mechanical testing of a low-porosity nanotube paper. (C) 2012 Elsevier Ltd. All rights reserved.

关键词： distinct element method Carbon nanotubes Van der Waals interactions

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Development of a 3D numerical model for simulating a blast wave propagation system considering me position of the blasting hole and in-situ discontinuities

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RUDARSKO-GEOLOSKO-NAFTNI ZBORNIK 2022年第2期37卷 67-78页

作者： Yari, Mojtaba Ghadyani, Daniyal Jamali, Saeed Malayer Univ Fac Engn Dept Min Engn Malayer Iran Fannavaran Vira Pasargad Co Tehran Iran Sazbon Pajouh Consulting Engineer Co Tehran Iran

Blasting operations are one of the most important parts of geotechnical and mining projects. Most rocks naturally have a series of discontinuities that significantly affect their responses to blast waves. In this paper, the propagation of a blast wave in one intact rock and four rocks with different joint conditions are simulated by a 3-dimensional distinct element code. The results showed that the joint in the model acted as a wave barrier and passed part of the waves, absorbed a portion, and reflected the remaining part into the model. In other words, a discontinuity reduces the energy of the wave and causes more wave attenuation. In addition, a shorter distance between the joint and the hole causes slower wave propagation and greater damping. Moreover, the results showed that the smaller the angle between the discontinuity and axis of the blast holes, the more stress occurs in the rock bench.

关键词： Blast wave 3D numerical analysis jointed rock distinct element method

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distinct element modeling of the dynamic response of a rocking podium tested on a shake table

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EARTHQUAKE ENGINEERING & STRUCTURAL DYNAMICS 2021年第5期50卷 1469-1475页

作者： Malomo, Daniele Mehrotra, Anjali DeJong, Matthew J. McGill Univ Dept Civil Engn & Appl Mech Montreal PQ Canada Univ Minho Dept Civil Engn ISISE P-4800058 Guimaraes Portugal Univ Calif Berkeley Dept Civil & Environm Engn Berkeley CA 94720 USA

A blind prediction contest was organized to evaluate the ability of different modeling approaches to simulate the seismic rocking response of a full-scale four-column podium structure. The structure was tested on a shake table, and was subjected to two bidirectional ground motion ensembles comprising 100 synthetic records each. This short communication presents the main assumptions and results from the model, developed using the distinct element method, which provided the second-best prediction of the experimental results. A comparison of the model predictions and the experimental results demonstrates that the numerical model was generally able to reproduce the large displacements induced by the more intense ground motion ensemble, while tending to overestimate the displacements of the less intense earthquake ensemble. This overestimation of the response was reduced through the inclusion of damping in the system. However, the addition of damping greatly increased the solve time, which is problematic for a competition, and in the case of the more intense ground motion ensemble also resulted in an underprediction of the maximum response of the structure.

关键词： blind prediction contest distinct element method dynamic analysis rocking shake‐ table test

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Study on the Effect of Loading method on Mechanical Behavior of Rockbolt Based on DEM Modeling

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INTERNATIONAL JOURNAL OF GEOMECHANICS 2022年第7期22卷

作者： Han, Tao Jin, Changyu Hou, Xiaole Liu, Xiaobo Lu, Yu Liu, Dong Northeastern Univ Intelligent Mine Res Ctr Shenyang 110819 Peoples R China Northeastern Univ Minist Educ Safe Min Deep Met Mines Key Lab Shenyang 110819 Peoples R China MCC Northern Engn & Technol Corp Dalian Dalian 116600 Peoples R China Chinese Acad Sci Shenyang Inst Automat SIA Shenyang 110169 Peoples R China Shantou Univ Coll Engn Shantou 515063 Peoples R China

Fully grouted rockbolt is a form of reinforcement commonly used in underground projects. Its mechanical behavior is of vital importance to enhancing the stability of surrounding rock masses. To investigate the effect of different loading methods on the mechanical behaviors of rockbolt, the distinct element code PFC2D was adopted to simulate the pullout test on rockbolt and a compression test on the bolted rock mass, with Hongtoushan Copper Mine as the engineering background. The stress distribution along rockbolt and the maximum pullout capacity were analyzed. The results indicated that the loading method has significant effects on the mechanical behaviors of rockbolt. In the pullout test, the peak stress in the rockbolt always occurs near the free face. As the rock mass is a passive load-bearing component, the cracks and weak intercalations in the rock mass have little effect on the mechanical behaviors of the rockbolt. Meanwhile, as the external load acts directly on the outer end of rockbolt, the effect of the bearing plate cannot be reflected. However, in the compression test on the bolted rock mass, the peak stress in the rockbolt gradually transfers to greater depth. The existence of cracks and weak intercalations have an impact on the mechanical behaviors of the rockbolt. In addition, with increasing size of the bearing plate, the maximum pullout capacity of the rockbolt gradually increases. Comparison of the simulation results showed that the maximum pullout capacity obtained by the pullout test on a rockbolt is higher than that obtained by the compression test on a bolted rock mass. Therefore, appropriate reduction of the maximum pullout capacity obtained by the pullout test is suggested for rockbolt design, and the reduction factor should be in the range of 0.7-0.8.

关键词： Fully grouted rockbolt Rockbolt pullout test Compression test on bolted rock mass Mechanical behavior distinct element method

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Influence of Bond Pattern on the in-plane Behavior of URM Piers

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INTERNATIONAL JOURNAL OF ARCHITECTURAL HERITAGE 2021年第10期15卷 1492-1511页

作者： Malomo, D. DeJong, M. J. Penna, A. Univ Calif Berkeley Dept Civil & Environm Engn 760 Davis Hall Berkeley CA 94720 USA Univ Pavia Dept Civil Engn & Architecture Pavia Italy

The overall seismic resistance of unreinforced masonry (URM) systems that exhibit box-behavior mainly relies on the lateral force capacity of structural components. Despite the fact that it is widely accepted that masonry bond pattern might considerably affect the in-plane performance of URM members, this aspect has not fully addressed experimentally or numerically. In this paper, calibrated numerical models, developed within the framework of the distinct element method, are used to simulate the quasi-static lateral response of URM piers under several combinations of boundary conditions, vertical pressures and aspect ratios, as well as a large number of typically-employed periodic and quasi-periodic bond patterns. The employment of time, size and mass scaling, and dynamic relaxation procedures, combined with the introduction of equivalent interface properties to represent the effect of cyclic damage through monotonic loading schemes, provided a significant reduction of computational cost, thus enabling a comprehensive parametric study to be carried out within an acceptable timeframe. The results show that the bond pattern has an appreciable influence on the response of laterally-loaded URM panels, motivating the possibility of including this aspect in the assessment of existing URM structures. Analytical formulations were also inferred by fitting numerical data, thus enabling the findings of this work to be readily implemented in assessment using simplified models.

关键词： Bond pattern distinct element method in-plane numerical modeling unreinforced masonry

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