Constitutive modelling of fibre-reinforced sand based on the concept of effective skeleton stress and void ratio

Huang, Mian (2022) Constitutive modelling of fibre-reinforced sand based on the concept of effective skeleton stress and void ratio. PhD thesis, University of Glasgow.

Abstract

The inclusion of flexible fibres such as polypropylene and waste or natural fibres is an effective method for soil improvement, as it can significantly enhance soil strength. Though a lot of research has been done on fibre-reinforced sand (FRS), a simple and practical constitutive model, essential for assessing the stability and serviceability of fibre-reinforced slopes/foundations, has not yet been developed. A new method for constitutive modelling of fibre-reinforced sand (FRS) is proposed in this study. The new model has also been used to simulate the mechanical behaviour of FRS prepared by different methods.

In the new modelling approach, FRS is considered as a composite material with host sand and flexible fibres. It is assumed that the strain of FRS is dependent on the deformation of the sand skeleton only. 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 fibre inclusion. The effective skeleton stress is dependent on the shear strain level, and the effective skeleton void ratio is affected by the fibre content and sample preparation method. A critical state FRS model in the triaxial stress space is proposed using the effective skeleton stress and void ratio. Four parameters are introduced to characterise the effect of fibre inclusion on the mechanical behaviour of sand, all of which can be easily determined based on triaxial test data on FRS, without measuring the stress-strain relationship of individual fibres. Triaxial compression test results validate the model on fibre-reinforced sands under loading conditions with various confining pressures, densities and stress paths. Potential improvement in the model for incorporating fibre orientation anisotropy is discussed.

It is well known that the mechanical behaviour of pure sand depends on the internal soil structure, which can be affected by sample preparation methods. For FRS, the sample preparation methods influence the internal structure of the sand skeleton and the distribution of fibre orientation and sand-fibre interaction. The effect of sample preparation methods on the mechanical behaviour of FRS has been investigated using comprehensive drained triaxial compression tests. The soil samples have been prepared by moist tamping (MT) and moist vibration (MV). There is a small difference in the stress-strain relationship of pure sand with different sample preparation methods. But the response of FRS is dramatically different. Under the same initial conditions of void ratio, confining pressure and fibre content, FRS prepared using the MV method shows 30–50% higher peak deviator stress and a much less dilative response. The newly developed constitutive model has been used to predict the mechanical behaviour of FRS prepared using the MT and MV methods.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Colleges/Schools: College of Science and Engineering > School of Engineering
• Supervisor's Name: Gao, Dr. Zhiwei and Shire, Dr. Thomas
• Date of Award: 2022
• Depositing User: Theses Team
• Unique ID: glathesis:2022-82671
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 03 Feb 2022 16:42
• Last Modified: 08 Apr 2022 16:53
• Thesis DOI: 10.5525/gla.thesis.82671
• URI: https://theses.gla.ac.uk/id/eprint/82671

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