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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

Surface-mounted bender elements for measuring horizontal shear wave velocity of soils

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2008年第11期9卷 1490-1496页

作者： Yan-guo ZHOU yun-min chen Yoshiharu ASAKA Tohru ABE MOE Key Laboratory of Soft Soils and Geoenvironmental Engineering Zhejiang University Hangzhou 310027 China Institute of Geotechnical Engineering Zhejiang University Hangzhou 310027 China Institute of Technology Shimizu Corporation Tokyo 135-8530 Japan

The bender element testing features its in-plane directivity, which allows using bender elements to measure the shear wave velocities in a wider range of in-plane configurations besides the standard tip-to-tip alignment. This paper proposed a novel bender element testing technique for measuring the horizontal shear wave velocity of soils, where the bender elements are surface- mounted and the axes of the source and receiver elements are parallel to each other. The preliminary tests performed on model ground of silica sand showed that, by properly determining the travel distance and time of the shear waves, the surface-mounted bender elements can perform as accurately as the conventional "tip-to-tip" configuration. Potentially, the present system provides a promising nondestructive tool for characterizing geomaterials and site conditions both in laboratory and in the fields.

关键词： Bender elements Shear wave velocity Model test Nondestructive evaluation Surface-mounted Sand

A new equation for dielectric permittivity of saturated soils based on polarization mechanics

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2008年第3期9卷 293-302页

作者： Ren-peng chen yun-min chen Wei XU Zhi-gang LIANG Wei FENG MOE Key Laboratory of Soft Soils and Geoenvironmental Engineering Zhejiang University Hangzhou 31002 7 China Institute of Geotechnical Engineering Zhejiang University Hangzhou 310027 China Design Institute of Architecture of Hangzhou Hangzhou 310001 China Lexmark lnternational inc. Lexinton KY 40511 USA

Based on polarization mechanisms, such as electronic, ionic and orientational polarizations, a new equation for dielectric permittivity of soil is proposed to interpret the dielectric behavior of a mixture like soil, in terms of polarization process of its components and the interactions between its components. The dielectric permittivity is expressed in terms of a fre-quency-dependent part and a frequency-independent part. These two parts correspond to polarizations occurred at different fre-quency range. It is a new volumetric mixing model with theoretical background. Based on time domain reflectometry (TDR) measurements of saturated soil samples and test data from literature, comparisons of this model with some well established mixing models show that the curves for saturated sand soils and slurries resulted from the new equation, which agree well with TDR measurements, are close to those calculated from Birchak's model.

关键词： Dielectric permittivity Saturated soils Polarization Time domain reflectometry (TDR)

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

Investigation of migration of pollutant at the base of Suzhou Qizishan landfill without a liner system

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2009年第3期10卷 439-449页

作者： Hai-jian XIE yun-min chen Liang-tong ZHAN Ren-peng chen Xiao-wu TANG Ru-hai chen Han KE MOE Key Laboratory of Soft Soils and Geoenvironmental Engineering Zhejiang University Hangzhou 310058 China College of Civil Engineering and Architeeture Zhejiang University Hangzhou 310058 China

We investigated migration of pollutant at the base of the Suzhou landfill after it had been operated for 13 years. The investigation was carried out by performing chemical analyses on the soil samples taken from the silty clay deposit. Concentrations of chloride, chemical oxygen demand （COD） and the heavy metals in the soil samples were determined using the standard methods. The experimental data showed that the maximum migration depth of chloride was more than 10 m, while the maximum migration depth of COD varied between 1 and 3.5 m. It is believed that the difference is attributed to the variation in diffusion rate and leachate-soil interaction. The chloride profiles also indicated that adveetion may be the dominant contaminant transport mechanism at this site. The total contents ofCu, Pb and Cr are very close to the background levels and the concentration values of these metals mainly are lower than the threshold values specified by the Chinese soil quality standard and the European one. The water-extractable concentrations of COD in the surface of the silty clay generally exceed the limit value specified by the Chinese standard. The concentrations of copper and chromium in pore water are 1-2 orders of magnitude less than the total concentrations of these heavy metals within the soils, implying that heavy metals are mainly adsorbed by the soil particles. Finally, remediation methods were suggested for this landfill site.

关键词： Uncontrolled landfill Field investigation Contaminant migration Soil contamination Heavy metals Organic contaminants Chloride

A semi-analytical method for the analysis of pile-supported embankments

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2012年第11期13卷 888-894页

作者： Wan-huan ZHOU Ren-peng chen Lin-shuang ZHAO Zheng-zhong XU yun-min chen Department of Civil and Environmental Engineering University of Macao Macao China MOE Key Laboratory of Soft Soils and Geoenvironmental Engineering Department of Civil Engineering Zhejiang University Hangzhou 310058 China

In this paper,a semi-analytical method for the analysis of pile-supported embankments is *** mathematic model describes the cooperative behavior of pile,pile cap,foundation soil,and embankment *** on Terzaghi's 1D consolidation theory of saturated soil,the consolidation of foundation soil is *** embankments with two different types of piles:floating piles and end-bearing piles are investigated and *** results of axial force and skin friction distributions along the pile and the settlements of pile-supported embankments are *** is found that it takes a longer time for soil consolidation in the embankment with floating piles,compared with the case using end-bearing *** differential settlement between the pile and surrounding soil at the pile top is larger for the embankment with end-bearing piles,compared with the case of floating piles.

关键词： Pile-supported embankment Soil arching Load transfer Equal settlement plane Soft soils

Nonlinear analysis of pile groups subjected to combined lateral and torsional loading

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2020年第3期21卷 179-192页

作者： Ling-gang KONG Zhong-chang ZHANG yun-min chen Institute of Geotechnical Engineering College of Architectural and Civil EngineeringZhejiang UniversityHangzhou 310058China

An empirical approach has been developed to analyze the nonlinear response of a pile group with arbitrarily distributed piles subjected to combined lateral and torsional *** this approach,the concept of instantaneous twist center is applied to analyze the displacement relationship of pile heads and establish the static equilibrium equations of the pile *** horizontal interaction among the individual piles is considered through the generalized *** coupling effect of lateral resistance on the torsional resistance of each pile is quantified using an empirical factorβ;the lateral and torsional nonlinear responses of individual piles are modeled by p-y andτ-θcurves,*** proposed approach not only captures the most significant aspect of the group effect and coupling effect in a pile group subjected to combined lateral and torsional loading,but also automatically updates p-multipliers of individual piles based on pile cap *** proposed approach was verified using results of model tests on pile groups subjected to lateral loading,torsional loading,and combined lateral and torsional loading,*** general,the pile cap response and the transfer of applied loads in the pile groups agree well with the test results.

关键词： Combined lateral and torsional loading Pile groups Twist center p-multiplier Group effect

Pile foundation of high-speed railway undergoing repeated groundwater reductions

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2021年第4期22卷 277-295页

作者： Xue-cheng BIAN Lei FU Chuang ZHAO yun-min chen MOE Key Laboratory of Soft Soils and Geoenvironmental Engineering Department of Civil EngineeringZhejiang UniversityHangzhou 310058China

Long-pile groups of railway foundation undergo excessive settlements after groundwater reductions,which may exceed the settlement limit and threaten the safe operation of high-speed ***,the effect of groundwater reduction on a long-pile group(greater than 20 m in length)has not been fully understood,especially in respect of repeated *** this study,a centrifuge test was conducted to investigate the responses of pile groups in silty soils subjected to repeated falls in the water *** behavior of the piles was discussed based both on the test and on 3D numerical *** the derived coef-ficientβfor the axial force evaluation of the pile,the effect of lowering the water table on the railway pile foundation could be *** of the tests and numerical analyses indicated that the water table decline significantly increased the down-drag and axial force of the pile,causing significant settlement.A longer pile presented a larger axial force at the neutral ***,the incremental percentage of the axial force decreased with increasing pile length with the same water table *** of group effect,the displacement of soil next to the center pile was smaller than that near the corner piles and showed a similar trend as the axial force of the *** the water table fell,the static load ratio affecting the progress of pile settlement increased dis-advantageously,possibly inducing excessive pile settlement.A design method for railway pile foundations taking account of lowering groundwater was proposed with an example application,which provided a reference for similar projects.

关键词： High-speed railway Pile foundation settlement Centrifuge testing Numerical modelling Groundwater declining Drag load

土-膨润土隔离墙孔压静力触探非单调消散曲线研究（英文）

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2018年第4期19卷 277-288页

作者： Yu-chao LI Xing TONG yun chen Han KE yun-min chen Yi-duo WEN Qian PAN MOE Key Laboratory of Soft Soils and Geoenvironmental Engineering Zhejiang University Architectural Design and Research Institute of Zhejiang University Co. Ltd. College of Civil Engineering and Architecture Zhejiang University of Water Resources and Electric Power

目的:土-膨润土隔离墙的水力特性可通过孔压静力触探试验进行评价。本文旨在研究土-膨润土隔离墙中孔压消散试验产生非单调孔压消散曲线的原因,并对现有计算固结系数与渗透系数的方法在土-膨润土隔离墙中的适用性进行分析。创新点:1.首... 详细信息

目的:土-膨润土隔离墙的水力特性可通过孔压静力触探试验进行评价。本文旨在研究土-膨润土隔离墙中孔压消散试验产生非单调孔压消散曲线的原因,并对现有计算固结系数与渗透系数的方法在土-膨润土隔离墙中的适用性进行分析。创新点:1.首次在土-膨润土隔离墙中测得非单调的孔压消散曲线;2.本文认为在土-膨润土隔离墙中测得非单调孔压消散曲线是由于探头贯入过程中在填料及其包裹的土块中产生的超孔压不一致引起的,并且由于填料的低渗透性,孔压上升的时间较长;3.比较不同方法的分析结果,并推荐结果与实测相近的计算方法作为工程应用。方法:1.通过室内一维固结试验和柔性壁渗透试验,分别获得墙体材料的固结系数和渗透系数;2.通过现场土-膨润土隔离墙的孔压静力触探试验与孔压消散试验,获得相应的力学参数与孔压消散曲线;3.分别采用不同方法对墙体材料的固结系数和渗透系数进行计算,并将计算结果与室内试验结果进行比较。结论:1.填料的非均质性导致探头贯入过程中产生的超孔压存在重分布,这使得土-膨润土隔离墙中产生了非单调孔压消散曲线,并且由于填料的低渗透性,测得孔压上升的时间较长;2.四种计算固结系数的方法中,有三种结果与室内一维固结试验结果相近,另一种结果则明显偏大;3.四种计算渗透系数的方法中,基于太沙基固结理论的关系式得到的结果与室内柔壁渗透试验结果相近,另两种经验公式得到的结果偏小,而基于探头贯入数据计算的渗透系数则偏大。

关键词：孔压静力触探消散试验土-膨润土隔离墙固结系数渗透系数