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Spatial Strategy for Quality Labor in Rural Development——A Case Study of Jiangsu Province, China

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Chinese Geographical Science 2007年第2期17卷 117-126页

作者： sun yifei WANG Hongyang Department of Geography California State University Northridge Los Angeles 91330 USA Department of Urban and Resources Sciences Nanjing University Nanjing 210093 China

This study examines the issue of high-quality labor in rural enterprises of China. It develops a spatial strategy which consists of two dimensions: geographical space and administrative space. Different combinations of these two dimensions form a variety of approaches such as local internalization, local externalization, regional/national inter- nalization, and regional/national externalization. In the local internalization approach, rural enterprises hire such high-quality labor and ask them to work on site, while in the local externalization approach, rural enterprises seek help from employees working in other local enterprises. In the regional/national internalization approach, rural enterprises set up research and development centers in big cities to take advantages of the high-quality labor pool there. Finally in the regional/national externalization approach, rural enterprises hire people from big cities on temporary contracts. Three approaches, hiring retired technical workers, shuttling between the rural site and country seats, and setting up R&D centers in big cities are demonstrated through cases in Zhangjiagang, a leading county-level city in the southern Jiangsu Province. It is argued that rural enterprises need to broaden their perspectives of administrative space and geographical space and think creatively to deal with the shortage of quality labor in rural settings.

关键词： skilled labor quality labor rural development spatial strategy China

Dilation and breakage dissipation of granular soils subjected to monotonic loading

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Acta Mechanica Sinica 2016年第6期32卷 1065-1074页

作者： yifei sun Yang Xiao Hua Ji Faculty of Engineering and Information Sciences University of Wollongong School of Civil and Transportation Engineering Hohai University College of Civil Engineering Chongqing University

Dilation and breakage energy dissipation of four different granular soils are investigated by using an energy balance equation. Due to particle breakage, the dilation curve does not necessarily pass through the origin of coordinates. Breakage energy dissipation is found to increase significantly at the initial loading stage and then gradually become stabilised. The incremental dissipation ratio between breakage energy and plastic work exhibits almost independence of the confining pressure. Accordingly, a plastic flow rule considering the effect of particle breakage is suggested. The critical state friction angle is found to be a combination of the basic friction between particles and the friction contributed by particle breakage.

关键词： Dilation Particle breakage Granular soil Energy dissipation

Effect of integrating memory on the performance of the fractional plasticity model for geomaterials

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Acta Mechanica Sinica 2018年第5期34卷 896-901页

作者： yifei sun Yufeng Gao Shunxiang Song Key Laboratory of Ministry of Education for Geomechanics and Embankment Engineering Hohai UniversityNanjing 210098China

A fractional plasticity model for geomaterials is proposed by using the fractional *** to the integral definition of the fractional derivative,the range of load memory for calculating the flow direction may influence the subsequent model ***,an investigation on the memory dependence of the model was *** was found that the load memory affected the stress-dilatancy behavior of the *** to the loss of memory from zero-to confiningstress states,slightly higher strain is reported,whereas an insignificant difference in the predicted deviator stress is ***,for engineering applications,starting the memory from the zero-stress state,which avoids mathematical complexity,is suggested.

关键词： Plasticity Fractional calculus Memory

A grading parameter for evaluating the grading-dependence of the shear stiffness of granular aggregates

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Particuology 2018年第1期16卷 193-198页

作者： yifei sun Yang Shen Chen Chen Key Laboratory of Ministry of Education for Ceomechanics and Embankment Engineering Jiangsu Research Center for Ceotechnical Engineering Technology Hohai University Nanjing 210098 China

To capture the grading-dependence of the shear stiffness of heterogeneous granular aggregates, a new grading parameter that considered the size distribution of the entire aggregates was developed. Both the coefficient of uniformity and median particle size decreased with increasing the grading parameter. A general increase of the shear stiffness with increasing the grading parameter was observed. Compari- son with experimental results revealed that the proposed grading parameter had a stronger correlation with the material constants of Hardin＇s stiffness formula than the coefficient of uniformity, which is a traditional grading parameter.

关键词： Shear stiffness Grading Coefficient of uniformity Particle size

Compressibility dependence on grain size distribution and relative density in sands

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Science China(Technological Sciences) 2015年第3期58卷 443-448页

作者： sun yifei XIAO Yang HANIF Khairul Fikry Faculty of Engineering and Information Sciences University of Wollongong College of Civil Engineering Chongqing University Faculty of Engineering Computing and Mathematics University of Western Australia

A framework of continuum breakage mechanics was used to investigate the dependence of compressibility on grain size distribution(GSD)as well as relative density of *** dependence on GSD was considered by employing a GSD index and relative density dependence was reflected by varying the plastic-breakage coupling *** of the experimental results including isotropic compression and one-dimensional compression of sands with different relative densities and GSDs revealed that sand compressibility increased with the increasing GSD index and plastic-breakage coupling *** coupling angle decreased with increasing relative density,indicating that grains would break more in sand with comparatively high relative density.

关键词： grain size distribution density compression grain breakage thermo-mechanics

FRACTIONAL ORDER MODELLING OF THE CUMULATIVE DEFORMATION OF GRANULAR SOILS UNDER CYCLIC LOADING

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Acta Mechanica Solida Sinica 2015年第6期28卷 647-658页

作者： yifei sun Yang Xiao Khairul Fikry Hanif Institute for Mathematics and Its Applications University of Wollongong State Key Laboratory of Coal Mine Disaster Dynamics and Control Chongqing University Key Laboratory of New Technology for Construction of Cities in Mountain Area Chongqing University College of Civil Engineering Chongqing University Faculty of Engineering Computing and MathematicsUniversity of Western Australia

To model the cumulative deformation of granular soils under cyclic loading, a mathematical model was proposed. The power law connection between the shear strain and loading cycle was represented by using fractional derivative approach. The volumetric strain was characterized by a modified cyclic flow rule which considered the effect of particle breakage. All model parameters were obtained by the cyclic and static triaxial tests. Predictions of the test results were provided to validate the proposed model. Comparison with an existing cumulative model was also made to show the advantage of the proposed model.

关键词： cumulative deformation cyclic stress cyclic flow rule fractional derivative granular soil

Development and application of state-dependent fractional plasticity in modeling the non-associated behavior of granular aggregates

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Acta Mechanica Solida Sinica 2017年第5期30卷 507-519页

作者： yifei sun Shunxiang Song Yang Xiao Jiancheng Zhang Key Laboratory of Ministry of Education for Geomechanics and Embankment Engineering College of Civil and Transportation Engineering Hohai University Nanjing 210098 China. College of Civil and Transportation Engineering Hohai University Nanjing 210098 China. State Key Laboratory of Coal Mine Disaster Dynamics and Control School of Civil Engineering Chongqing University Chongqing 400450 China School of Naval Architecture and Civil Engineering Jiangsu University of Science and Technology Jiangsu 215600 China

To characterize the constitutive behavior of granular aggregates, a non-associated plasticity model with two different yield and plastic potential surfaces was usually used. However, in this paper, a state-dependent fractional elastoplastic model is proposed by only perform- ing the first- and fractional-order differentiations of the yield function. The non-associated plastic flow is obtained without using any plastic potential functions. The state dependence is considered by correlating the fractional order with a state parameter. The model is then validated by simulating a series of test results of different granular aggregates, including sand, ballast and rockfill, under a variety of loading conditions.

关键词： Fractional plasticityGranular aggregatesNon-associated flow

A particle-breakage critical state model for rockfill material

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Science China(Technological Sciences) 2015年第7期58卷 1125-1136页

作者： XIAO Yang sun yifei HANIF Khairul Fikry Key Laboratory of New Technology for Construction of Cities in Mountain Area Chongqing University College of Civil Engineering Chongqing University Faculty of Engineering and Information Sciences University of Wollongong Faculty of Engineering Computing and Mathematics University of Western Australia

Particle breakage has a significant influence on the stress-strain and strength behavior of rockfill material.A breakage critical state theory(BCST)was proposed to describe the evolution of particle *** breakage critical state line in the breakage critical state theory was correlated with the breakage factor,which was fundamentally different from that of the original critical state theory.A simple elastoplastic constitutive model was developed for rockfill in the frame of *** associated flow rule was adopted in this ***,contractive and distortional hardening rules were suggested in view of the particle *** was observed that the proposed model could well represent the complex deformation behaviors of rockfill material,such as the strain hardening,post-peak strain softening,volumetric contraction,volumetric expansion,and particle breakage under different initial confining pressures.

关键词： rockfill material particle breakage critical state theory hardening rule constitutive model

Modeling of strength and deformation of overconsolidated clays based on bounding surface plasticity

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Science China(Technological Sciences) 2016年第9期59卷 1452-1462页

作者： XIAO Yang[[ LIU HanLong sun yifei LIU Hong State Key Laboratory of Coal Mine Disaster Dynamics and Control Chongqing University Key Laboratory of New Technology for Construction of Cities in Mountain Area Chongqing University College of Civil Engineering Chongqing University Faculty of Engineering and Information Sciences University of Wollongong

An elastoplastic constitutive model for overconsolidated clays is established in the framework of the critical state theory and bounding surface plasticity theory. The bounding surface is defined as the maximum yield surface in the loading history. A yielding ratio, i.e., an internal variant, is defined as the size ratio of the current yield surface to the corresponding bounding surface. The yielding ratio instead of the overconsolidation ratio(OCR) is used to evaluate the strength and stress-strain behaviors of overconsolidated clays in the shearing process. The bounding stress ratio incorporating the effect of the yielding ratio is used to characterize the potential failure strength of the overconsolidated clays. The dilation stress ratio taking into account the effect of the yielding ratio is applied to describe the dilatancy behaviors of the overconsolidated clays. Comparisons between model predictions and test data show that the proposed model could well capture the strength and stress-strain behaviors of normally consolidated and overconsolidated clays.

关键词： overconsolidated clay overconsolidated ratio critical state theory yielding ratio peak state strength dilatancy