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Simulation of the relationship between porosity and tortuosity in porous media with cubic particles

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Chinese Physics B 2012年第10期21卷 1-8页

作者：唐晓武孙祖峰程冠初 moe key laboratory of soft soils and geoenvironmental engineering Department of Civil EngineeringZhejiang University

Tortuosity is an important parameter used in areas such as vascular medicine,neurobiology,and the field of soil permeability and diffusion to express the mass transport in porous *** is a function of the porosity and the shape and distribution of *** this paper,the tortuosity of cubic particles is *** the assumption that the porous medium is homogeneous,the problem is converted to the micro-level over a unit cell,and geometry models of flow paths are *** three-dimensional（3D） cells,the flow paths are too complicated to ***,the 3D models are converted to two-dimensional（2D） models to simplify the calculation *** is noticed that the path in the 2D model is shorter than that in the 3D *** a result,triangular particles and the interaction are also taken into consideration to account for the longer distance *** have proposed quadrate particle and interaction（QI） and quadrate and triangular particle（QT） models with cubic *** models have shown good agreement with the experimental *** is also found that they can predict the toruosities of some kinds of porous media,like freshwater sediment and Negev chalk.

关键词： tortuosity porosity porous media cubic particles

Shear wave velocity-based liquefaction evaluation in the great Wenchuan earthquake: a preliminary case study

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Earthquake engineering and engineering Vibration 2009年第2期8卷 231-239页

作者： Zhou Yanguo,Chen Yunmin and Ling Daosheng moe key laboratory of soft soils and geoenvironmental engineering,Institute of Geotechnical engineering,Zhejiang University,Hangzhou 310058,China Assistant Professor Professor moe key laboratory of soft soils and geoenvironmental engineering Zhejiang University Hangzhou 310058 China moe key laboratory of soft soils and geoenvironmental engineering Zhejiang University 388 Yuhangtang Road Hangzhou 310058 China

The great Wenchuan earthquake （Ms= 8.0） in 2008 caused severe damage in the western part of the Chengdu Plain. soil liquefaction was one of the major causes of damage in the plain areas, and proper evaluation of liquefaction potential is important in the definition of the seismic hazard facing a given region and post-earthquake reconstruction. In this paper, a simplified procedure is proposed for liquefaction assessment of sandy deposits using shear wave velocity （V）, and soil liquefaction from the Banqiao School site was preliminarily investigated after the earthquake. Boreholes were made at the site and shear wave velocities were measured both by SASW and down-hole methods. Based on the in-situ soil information and V profiles, the liquefaction potential of this site was evaluated. The results are reasonably consistent with the actual field behavior observed after the earthquake, indicating that the proposed procedure is effective. The possible effects of gravel and fines contents on liquefaction of sandy soils were also briefly discussed.

关键词： liquefaction Wenchuan earthquake shear wave velocity spectral analysis of surface waves (SASW) hazarddefinition

Analysis of diffusion-adsorption equivalency of landfill liner systems for organic contaminants

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Journal of Environmental Sciences 2009年第4期21卷 552-560页

作者： XIE Haijian, CHEN Yunmin, KE Han, TANG Xiaowu, CHEN Renpeng moe key laboratory of soft soils and geoenvironmental engineering, Zhejiang University, Hangzhou 310027, China. [a]moe key laboratory of soft soils and geoenvironmental engineering Zhejiang University Hangzhou 310027 China

The equivalence between multilayered barriers regarding diffusion and adsorption was studied. The bottom boundary of the liner system is defined by assuming concentration continuous and flux continuous conditions of the contaminant between the bottom liner layer and the underlying soil. Five different liner systems were compared in terms of solute breakthrough time. The results of the analysis showed that breakthrough time of the hydrophobic organic compounds for a 2-meter-thick compacted clay liner （CCL） could be 3-4 orders of magnitude is greater than the breakthrough time for a geosynthetic clay liner （GCL） composite liner. The GM/GCL and GM/CCL composite liner systems provide a better diffusion barrier for the hydrophilic organic compounds than that for the hydrophobic compounds due to their different Henry＇s coefficient. The calculated breakthrough times of the organic contaminants for the Chinese standard liner systems were found to be generally greater than those for the GCL alternatives, for the specific conditions examined. If the distribution coefficient increases to 2.8 for the hydrophobic compounds or 1.0 for the hydrophilic compounds, the thickness of the attenuation layer needed to achieve the same breakthrough time as the standard liner systems can be reduced by a factor of about 1.9-2.4. As far as diffusive and adsorption contaminant transport are concerned, GM or GCL is less effective than CCL.

关键词： liner system equivalency organic contaminant landfill diffusion adsorption

Steady-state response of a saturated half-space with an overlying dry layer subjected to a moving load

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Journal of Zhejiang University-Science A(Applied Physics & engineering) 2012年第1期13卷 33-43页

作者： An-feng HU Bo SUN Kang-he XIE moe key laboratory of soft soils and geoenvironmental engineering Zhejiang University Hangzhou 310058 China

In this paper,the steady-state response of a saturated half-space with an overlying dry layer subjected to a moving rectangular load is *** governing partial differential equations are solved using the Fourier *** solutions in time-space domain are expressed in terms of infinite Fourier type integrals,which can be evaluated only by numerical *** results show that the influence of a drained or undrained interface on the response is related to the permeability of the underlying saturated ***,the effect due to the upper dry layer is associated with the thickness of the layer.

关键词： Steady-state response Moving load Saturated half-space Overlying dry layer Fourier transform Drained orundrained interface

A 2.5D finite element approach for predicting ground vibrations generated by vertical track irregularities

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Journal of Zhejiang University-Science A(Applied Physics & engineering) 2011年第12期12卷 885-894页

作者： Xue-cheng BIAN Chang CHAO Wan-feng JIN Yun-min CHEN moe key laboratory of soft soils and geoenvironmental engineering Department of Civil Engineering Zhejiang University Hangzhou 310058 China

Dynamic responses of track structure and wave propagation in nearby ground vibration become significant when train operates on high speeds. A train-track-ground dynamic interaction analysis model based on the 2.5D finite element method is developed for the prediction of ground vibrations due to vertical track irregularities. The one-quarter car mode,1 is used to represent the train as lumped masses connected by springs. The embankment and the underlying ground are modeled by the 2.5D finite element approach to improve the computation efficiency. The Fourier transform is applied in the direction of train＇s movement to express the wave motion with a wave-number. The one-quarter car model is coupled into the global stiffness matrix describing the track-ground dynamic system with the displacement compatibility condition at the wheel-rail interface, including the irregularities on the track surface. Dynamic responses of the track and ground due to train＇s moving loads are obtained in the wave-number domain by solving the governing equation, using a conventional finite element procedure. The amplitude and wavelength are identified as two major parameters describing track irregularities. The irregularity amplitude has a direct impact on the vertical response for low-speed trains, both for short wavelength and long wavelength irregularities. Track irregularity with shorter wavelength can generate stronger track vibration both for low-speed and high-speed cases. For low-speed case, vibrations induced by track irregularities dominate far field responses. For high-speed case, the wavelength of track irregularities has very little effect on ground vibration at distances far from track center, and train＇s wheel axle weights becomes dominant.

关键词： High-speed railway 2.5D finite element method One-quarter car model Ground vibration Track irregularities

Accumulative deformation in railway track induced by high-speed traffic loading of the trains

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Earthquake engineering and engineering Vibration 2010年第3期9卷 319-326页

作者： Bian Xuecheng Jiang Hongguang Chen Yunmin Department of Civil engineering MOE Key Laboratory of Soft Soils and Geoenvironmental Engineering Zhejiang University Hangzhou 310058 China

Prediction and control of the permanent settlement of a track caused by traffic loading from trains is crucial to high-speed railway design and maintenance. In this study, a unified prediction model of accumulative deformation of geomaterials used in railway construction subjected to cyclic loadings is introduced and calibrated using physical model testing. Based on this versatile model, a calculation approach to determine the track structure settlement under repeated loadings caused by the movement of the wheel axle of the train is proposed. Regression analysis on the physical model testing is adopted to determine the parameters involved in the computational approach. Comparison of model test data and computed results shows that the parameters obtained from the back-analysis are consistent throughout the various testing conditions, and the proposed calculation approach is capable of satisfactorily predicting the accumulative settlement of the railway roadbed and subgrade soil for various axle loads and loading cycles. A case study of a high-speed railway is performed to demonstrate the feasibility of the proposed approach in realistic engineering applications. The computation results from the settlement development of a roadbed and subgrade soil are presented and discussed.

关键词： cyclic loading aggregate clay accumulative settlement high-speed railway

Seismic stability and permanent displacement of landfill along liners

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Science China(Technological Sciences) 2008年第4期51卷 407-423页

作者： CHEN YunMin GAO Deng ZHU Bin CHEN RenPeng moe key laboratory of soft Solis and geoenvironmental engineering Zhejiang UniversityHangzhou 310027China

The three-part wedge limit equilibrium method for seismic stability analysis of the landfill along liners is presented. The approximate solutions of the factor of safety and the yield acceleration coefficient are obtained. Parametric studies show that the interface strength of liners, the shear strength of waste and the height of retaining wall can influence the seismic stability of landfill along liners. The density and the shear wave velocity of the field waste are obtained by the borehole investigation and the spectral analysis of surface wave (SASW), respectively. The strain-dependent shear modulus and damping ratio of the artifical waste are obtained by the moderate-scale dynamic triaxial tests. The onedimensional (1D) equivalent linear dynamic response analysis is used to calculate the horizontal equivalent seismic coefficient-time history of the sliding landfill during earthquake. The seismic permanent displacement of the landfill along liners with different site conditons and heights is evaluated by the Newmark method. The catculated results show that ratio of ky /kmax, site conditions, the amplitude and frequency content of the bedrock motion can affect the seismic permanent displacement of the landfill along liners in some degree. Finally, the seismic stability and permanent displacements of three expanded configurations of a certain landfill case are analyzed.

关键词： landfill liner seismic stability permanent displacement Newmark method

Model tests on interaction between soil and geosynthetics subjected to localized subsidence in landfills

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Journal of Zhejiang University-Science A(Applied Physics & engineering) 2012年第6期13卷 433-444页

作者： Bin ZHU Deng GAO Jun-chao LI Yun-min CHEN moe key laboratory of soft soils and geoenvironmental engineering Department of Civil EngineeringZhejiang UniversityHangzhou 310058China

In a landfill, excessive tensile strains or failure of the liner system due to localized subsidence underneath the geosynthetic liner, is a concern in design and operation of the landfill. The localized subsidence can be commonly withstood by reinforcements such as geogrids. A total of nine model tests were carried out to study the influence of soil arching in overburden sandy soil on the geosynthetics and the interaction between the soil and the geosynthetics. The localized subsidence was modeled by a strip trapdoor under the geosynthetic reinforcements. The reinforcement includes several layers of polyvinylchlorid （PVC） membrane or both PVC membrane and a compacted clay layer. Test results show that the vertical soil pressure acting on the geosynthetics within the subsidence zone is strongly related to the deflection of the geosynthefics. The soil pressure acting on the deflected geosynthetics will decrease to a minimum value with respect to its deflection if the final deflection is large enough, and this minimum value is almost independent of the overburden height. Otherwise, the deflection of geosynthetics cannot result in a full degree of soil arching, and the soil pressure within the subsidence zone increases with the increase of overburden height. Deflections and strains of the geosynthetics obviously decrease with the increase of their tensile stiffness. The presence of a compacted clay layer buffer can therefore reduce both deflections and strains of the geosynthetics. Finally, a composite liner structure is recommended for landfills to withstand the localized subsidences.

关键词： Landfill soil arching Trapdoor Model test Geosynthetics

Shear wave velocity-based evaluation and design of stone column improved ground for liquefaction mitigation

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Earthquake engineering and engineering Vibration 2017年第2期16卷 247-261页

作者： Zhou Yanguo Sun Zhengbo Chen Jie Chen Yunmin Chen Renpeng moe key laboratory of soft soils and geoenvironmental engineering Institute of Geotechnical Engineering Zhejiang University Hangzhou 310058 China

The evaluation and design of stone column improvement ground for liquefaction mitigation is a challenging issue for the state of practice. In this paper, a shear wave velocity-based approach is proposed based on the well-defined correlations of liquefaction resistance （CRR）-shear wave velocity （V）-void ratio （e） of sandy soils, and the values of parameters in this approach are recommended for preliminary design purpose when site specific values are not available. The detailed procedures of pre- and post-improvement liquefaction evaluations and stone column design are given. According to this approach, the required level of ground improvement will be met once the target V of soil is raised high enough （i.e., no less than the critical velocity） to resist the given earthquake loading according to the CRR-V relationship, and then this requirement is transferred to the control of target void ratio （i.e., the critical e） according to the V-e relationship. As this approach relies on the densification of the surrounding soil instead of the whole improved ground and is conservative by nature, specific considerations of the densification mechanism and effect are given, and the effects of drainage and reinforcement of stone columns are also discussed. A case study of a thermal power plant in Indonesia is introduced, where the effectiveness of stone column improved ground was evaluated by the proposed V-based method and compared with the SPT-based evaluation. This improved ground performed well and experienced no liquefaction during subsequent strong earthquakes.

关键词： Liquefaction mitigation Stone column Shear wave velocity Void ratio Densification Ageing effect