Effective skeleton stress and void ratio for constitutive modeling of fiber-reinforced sand
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RESEARCH PAPER
Effective skeleton stress and void ratio for constitutive modeling of fiber-reinforced sand Zhiwei Gao1
•
Dechun Lu2 • Mian Huang1
Received: 23 October 2019 / Accepted: 3 May 2020 Ó The Author(s) 2020
Abstract Inclusion of flexible fibers such as polypropylene and polyester is an effective method for soil improvement, as it significantly enhances the soil strength and ductility. A proper constitutive model is essential for assessing the stability and serviceability of fiber-reinforced slopes/foundations. A new method for constitutive modeling of fiber-reinforced sand (FRS) is proposed. It assumes that the strain of FRS is dependent on the deformation of the sand skeleton only, while the effective skeleton stress and effective skeleton void ratio, which should be used in describing the dilatancy, plastic hardening and elastic stiffness of FRS, are affected by fiber inclusion. The effective skeleton stress is dependent on the shear strain level, and the effective skeleton void ratio is affected by the fiber content and sample preparation method. A critical state FRS model in the triaxial stress space is proposed using the concept of effective skeleton stress and void ratio. Four parameters are introduced to characterize the effect of fiber inclusion on the mechanical behavior of sand, all of which can be easily determined based on triaxial test data on FRS, without measuring the stress–strain relationship of individual fibers. The model is validated by triaxial compression test results on four fiber-reinforced sands under loading conditions with various confining pressures, densities and stress paths. Potential improvement in the model for incorporating fiber orientation anisotropy is discussed. Keywords Constitutive model Critical state Dilatancy Fiber-reinforced sand Triaxial compression List of symbols D Dilatancy relation e, es Void ratio and effective skeleton void ratio e0 Initial void ratio f Yield function G Elastic shear modulus Gf , Gs Specific gravity of fiber and sand H Hardening parameter for the yield function K Elastic bulk modulus L Loading index Mc Critical state stress ratio in triaxial compression p Mean effective stress pf Mean effective stress contribution from fibers q Deviator stress & Zhiwei Gao [email protected] 1
James Watt School of Engineering, University of Glasgow, Glasgow G12 8QQ, UK
2
Key Laboratory of Urban Security and Disaster Engineering of Ministry of Education, Beijing University of Technology, Beijing 100124, China
pa pc ps , qs wf vv , vf , vs ea , er eq ev eeq , eev epq , epv qf m ra , rr w gs , g
Atmospheric pressure Maximum fiber contribution to mean effective skeleton stress Effective skeleton stress Fiber content in weight Volume of the void, fibers and sand particles Axial strain and radial strain Shear strain Volumetric strain Elastic shear and volumetric strain Plastic shear and volumetric strain Volume fraction of fibers The Poisson’s ratio Effective axial and radial stress State parame
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