AbstractsBusiness Management & Administration

Analysing consolidation data to optimise elastic visco-plastic model parameters for soft clay

by Thu Minh Le

Institution: University of Technology, Sydney
Year: 2015
Record ID: 1073923
Full text PDF: http://hdl.handle.net/10453/34461


Analysing the behaviour of soft soils under embankments is a significant challenging task for geotechnical engineers. By having more insight into long term soil behaviour and understanding the key parameters influencing the results, there will be more chance to strategically plan and utilise the soft ground for construction purposes. The time–dependent behaviour of soft soils, especially the ground settlements under structural and non–structural loading, is considered as a significant issue, which has been studied for many decades. Prediction of creep settlement of soft soils is a challenging task, as a very long period of time counted in years is involved. Many theories have been proposed along with a large number of laboratory and field measurements in order to provide more precise knowledge of the time–dependent viscous behaviour of soft soils. However, there are still some disagreements between theoretical and practical studies, which may keep the accuracy of the predictions questionable. Among the great number of developed models for soft soils, the elastic visco–plastic model with the non–linear creep function is considered as an effective method to describe the long–term stress–strain behaviour of soft soils. However, the difficulties to determine the model parameters limit the application of the model in practice. Since the relationship between the effective stress and strain during the dissipation of the excess pore water pressure cannot be identified easily, in the current practice the creep strain limit ε_lm^vp and the creep coefficient ψo/V to form the creep function are determined based on the curve fitting of the experimental data after the end of the primary consolidation. As a result, the number of data points available for the curve fitting is limited, and the extremely long tests are required. Moreover, in the conventional procedure for the ease of the curve fitting, the time parameter to in the elastic visco–plastic, which is the time value of the reference time line in the space of ε-log(σ’z), has been assumed as the time at the end of primary consolidation process. Hence, based on this assumption of to, the reference time line would include viscous strain, which is contradict to the definition of a viscous free reference time line. Thus, the value of to influences not only the reference time line parameters, but also the parameters of the creep function. Additionally, the conventional determination approach for the model parameters is influenced by the thickness of the soil sample. Hence, the model parameters obtained by the conventional method may not be unique. As a result, the main objective of this research project is to propose a numerical solution to determine the model parameters for the elastic visco–plastic model adopting the trust–region reflective least square algorithm. The trust-region reflective least square algorithm is an advanced optimisation method for the non-linear equation system. A Crank–Nicolson finite difference scheme is applied to solve the coupled partial differential…