Modelling the time dependent behaviour of anisotropic soft clay using non-stationary flow surface theory

Nguyen, Dinh Hung (2021) Modelling the time dependent behaviour of anisotropic soft clay using non-stationary flow surface theory. PhD thesis, University of Nottingham.

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Prediction of the long-term deformation of a soft clay under different loading conditions has been a challenging task for geotechnical engineering since the time dependency of soft clay is a complex matter. This topic has attracted the attention of researchers for many decades. An insight into a scenario related to the time dependency of soft clay is a significant pathway to provide the best solution in geotechnical design for geo-structures constructed on soft ground. This thesis is made an attempt to study the time dependent behaviour of soft clay and proposed an advanced time dependent constitutive model, namely NSFS-SCLAY1S model which can capture the significant advanced features of soft clay regarding fabric anisotropy, destructuration of inter-particle bonding and time dependency. The model was developed based on the non-stationary flow surface theory (NSFS) which was proposed by Perzyna in 1964. The NSFS theory is a further development of inviscid elasto-plastic theory, in which a time variable parameter is introduced in the yield surface equation to obtain the simultaneous description of strain hardening and the effect of time. This means that the yield surface can change at any moment. The inherent framework from the classical elasto-plastic theory is used in determining the viscoplastic strain, leading to the simplification of the numerical solution. The preference of NSFS theory in this research is due to the limitation of overstress-based consititutive models of describing properly the creep behaviour of soft clay. The proposed NSFS-SCALY1S model, in contrast, is capable of capturing the strain rate effects and creep response of soft clay. In particular, it is able to simulate tertiary creep response, which is an important phase of creep behaviour which leads to creep failure of soft soil deposits.

Before development of an advanced time dependent constitutive model , namely NSFS-SCLAY1S which is capable of describing all significant features of soft clay such as fabric anisotropy, destructuration and time dependency, a preliminary time-dependent constitutive model using non-stationary flow surface (NSFS) in combination with a well-known Modified Cam Clay (MCC) model was developed first, called NSFS-MCC model. This model was focused on evaluation of the capacity the NSFS theory on prediction of the time dependency of soft clay so soft soil is assumed as an isotropic material. Both NSFS-SCLAY1S and NSFS-MCC models were verified qualitatively and quantitatively. Some elementary tests such as undrained triaxial compression & extension tests, oedometer tests and undrained triaxial creep tests were employed to verify the models. NSFS-SCLAY1S model reproduced very well the laboratory test results, proving its capacity to provide an optimum prediction of a practical geotechnical challenge. The detail of determination model parameters was presented and discussed.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Rezania, Mohammad
Triantafyllou, Savvas
Psimoulis, Panagiotis
Keywords: Time dependent behaviour, Anisotropic soft clay, Non-stationary flow surface theory
Subjects: T Technology > TA Engineering (General). Civil engineering (General) > TA 703 Engineering geology. Rock and soil mechanics
Faculties/Schools: UK Campuses > Faculty of Engineering > Department of Civil Engineering
Item ID: 66143
Depositing User: Nguyen, Dinh
Date Deposited: 31 Dec 2021 04:40
Last Modified: 31 Dec 2021 04:40

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