Seismic liquefaction countermeasures for waterfront slopes

Jafari Mehrabadi, Ahmad (2006) Seismic liquefaction countermeasures for waterfront slopes. Doctoral (PhD) thesis, Memorial University of Newfoundland.

[English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (151MB)

Abstract

A large number of the observed catastrophic effects during past earthquakes all over the globe including loss of human life, and drastic economic losses caused by severe damage to many structures are related to the occurrence of soil failure and large displacements caused by soil liquefaction. -- The Fraser River Delta in British Colombia is highly prone to liquefaction hazards, and a large amount of money is spent annually to mitigate the detrimental consequences of soil liquefaction in this region. In this respect, NSERC sponsored a Liquefaction Remediation Initiative (LRI) to assess and optimize the required seismic liquefaction countermeasures in the Fraser River Delta using a series of centrifuge experiments and numerical simulations. -- Optimization of liquefaction remediation techniques requires understanding their effectiveness at different levels of seismic intensity. This can be achieved if the seismic behavior of soil during an earthquake is accurately predicted. Numerical methods, accompanied by advanced constitutive models that have been validated in the past for liquefaction analysis, are able to achieve such a prediction. -- The primary objective of this research is to study the seismic behavior of waterfront slopes consisting of liquefiable sands in the Fraser River Delta and to assess the performance and effectiveness of liquefaction countermeasures for such slopes within the framework of the LRI project, based on numerical simulations. The numerical model used in this study is the multi-yield plasticity soil constitutive model, implemented in the finite element code Dynaflow. Other objectives followed in this research along with the mam one include: 1) calibrating and validating the numerical model to be used for liquefaction analysis in the Fraser River Delta, 2) studying the boundary effects caused by a rigid centrifuge container used in LRI on the seismic behavior of waterfront slopes, and 3) studying the effects of incomplete saturation on the sand seismic behavior within the process of numerical model calibration. -- The first step in this research is to calibrate the multi-yield plasticity soil constitutive model for Fraser River sand, and to validate the model based on the results of the LRI centrifuge test series. Therefore, this research presents in detail the procedures used for calibrating and validating the presented numerical model. Effects of incomplete saturation on the sand seismic behavior are also studied in this step. -- The second step in achieving the main objective of this research is to use the validated numerical model and extend the scope of the LRI centrifuge experiments for mitigation studies. This is desirable since the cost of centrifuge modeling is remarkably higher than that of numerical simulations. As the rigid container used in the LRI centrifuge experiments can significantly influence the slope seismic behavior, considerations regarding the effects of centrifuge rigid boundaries are presented along with the study on the effectiveness of liquefaction countermeasures, to investigate the scope and applicability of the LRI centrifuge tests for practical purposes. -- Finally, a summary of numerical studies on the performance and effectiveness of different seismic liquefaction countermeasures considered for a waterfront slope in the Fraser River Delta within the framework of the LRI project is presented in this research. The performance of several remediation techniques used in LRI is studied and discussed. -- In addition, a feasible mitigation solution is proposed for waterfront slopes with a performance comparable to that of the measures studied in LRI. Furthermore, fragility curves are used to represent the effectiveness of different remediation techniques at different earthquake intensities. It is shown that the effectiveness of liquefaction countermeasures strongly depends upon the level of seismic intensity.

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