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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

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

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

Influence of reaction piles on test pile response in a static load test

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Journal of Zhejiang University-Science A(Applied Physics & engineering) 2013年第3期14卷 198-205页

作者： Qian-qing ZHANG Shu-cai LI Zhong-miao ZHANG Geotechnical and Structural engineering Research Center Shandong University moe key laboratory of soft soils and geoenvironmental engineering Zhejiang University

This work presents a new analytical method to analyze the influence of reaction piles on the test pile response in a static load *** our method,the interactive effect between soil and pile is simulated using independent springs and the shear displacement method is adopted to analyze the influence of reaction piles on test pile ***,the influence of the sheltering effect between reaction piles and test pile on the test pile response is taken into *** cases are analyzed to verify the rationality and efficiency of the present *** method can be easily extended to a nonlinear response of an influenced test pile embedded in a multilayered soil,and the validity is also demonstrated using centrifuge model tests and a computer program presented in the *** present analyses indicate that the proposed method will lead to an underestimation of the test pile settlement in a static load test if the influence of the presence of reaction piles on the test pile response is neglected.

关键词： Test pile Reaction pile Shear displacement method Sheltering effect Multilayered soil

Molecular force mechanism of hydrodynamics in clay nanopores

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Journal of Zhejiang University-Science A(Applied Physics & engineering) 2023年第9期24卷 817-827页

作者： Shengjie WEI Yuchao LI Peng SHEN Yunmin CHEN moe key laboratory of soft soils and geoenvironmental engineering College of Civil Engineering and ArchitectureZhejiang UniversityHangzhou 310058China

Nanopores are prevalent within various clay morphologies,and water flow in clay nanopores is significant for various engineering *** this study,we performed non-equilibrium molecular dynamics(NEMD)simulations to reveal the molecular force mechanisms of water flow in clay *** water dynamic viscosity,slip length,and average flow velocity were obtained to verify the NEMD *** the water confined in the nanopores maintained a dynamic mechanical equilibrium state,each water lamina can be regarded as a simply supported *** applied driving force,the force from clay crystal layers,the force from compensating sodium ions,and the force from other water laminae were further calculated to investigate the force *** van der Wals barrier above the surface and hydraulic gradient lead to distribution differences in water oxygen atoms,which contribute to a net van der Waals resistance component of the force from clay crystal ***,the water molecules tend to rotate to generate the electrostatic resistance component of the force from clay crystal layers and balance the increasing hydraulic *** to the velocity difference,the water molecules in the slower lamina have a higher tendency to lag and generate a net electrostatic resistance force as well as a net van der Waals driving force on the water molecules in the faster lamina,which together make up the viscous force.

关键词： Molecular dynamics Hydrodynamics Clay Nanopore Molecular force Boundary effect Viscous force