Numerical modelling of earthquake induced liquefaction under irregular and multi-directional loading

This PhD thesis details the numerical investigation of earthquake-induced liquefaction using state-of-the-art research tools implemented in the in-house Imperial College Finite Element Program (ICFEP). The study draws particular emphasis on the role of the multi-directional and irregular nature of the seismic motion on liquefaction, aiming to enable better risk characterisation in engineering practice. The first part focusses on the role of the vertical seismic motion on sand liquefaction, which is largely neglected in design standards. The major contribution relates to a novel concept of liquefaction triggering due to the vertical ground motion, the impact of which was catastrophic during the 2010-2011 Canterbury Earthquake Sequence in New Zealand. Energy principles are adopted in P-wave propagation to aid the interpretation of the physical mechanism. The performance of two time-integration schemes are also compared to provide guidance on numerical geotechnical earthquake engineering problems involving compressional waves. The second part concerns suggested modifications to the constitutive model for sand to mitigate limitations identified in the first part in terms of the simulated undrained cyclic strength. The modified formulation is presented and calibrated based on published element testing and its performance is thoroughly assessed. The third part investigates the applicability of the Palmgren-Miner hypothesis in liquefaction evaluation through the equivalent number of stress cycles concept. The latter is directly applicable to the magnitude scaling factors used in liquefaction assessments, but also to the laboratory evaluated cyclic strength. A procedure to test this numerically is outlined. Based on the conclusions, guidelines for improved use are discussed. The final part of this thesis models a case study. The Mw 6.2 22nd February 2011 Christchurch seismic event in New Zealand was chosen for the analyses, as it presents a well-documented case. A thorough discussion on the inferred geotechnical parameters and on the calibration of the constitutive models is made. The selection of representative input ground motions is also presented in detail. The numerical predictions are compared against the monitoring and field data, but also against the predictions of the simplified liquefaction procedure.Open Acces

Caprock integrity and public perception studies of carbon storage in depleted hydrocarbon reservoirs

Capture and subsurface storage of CO2 is widely viewed as being a necessary component of any strategy to minimise and control the continued increase in average global temperatures. Existing oil and gas reservoirs can be re-used for carbon storage, providing a substantial fraction of the vast amounts of subsurface storage space that will be required for the implementation of carbon storage at an industrial scale. Carbon capture and storage (CCS) in depleted reservoirs aims to ensure subsurface containment, both to satisfy safety considerations, and to provide confidence that the containment will continue over the necessary timescales. Other technical issues that need to be addressed include the risk of unintended subsurface events, such as induced seismicity. Minimisation of these risks is key to building confidence in CCS technology, both in relation to financing/liability, and the development and maintenance of public acceptance. These factors may be of particular importance with regard to CCS projects involving depleted hydrocarbon reservoirs, where the mechanical effects of production activities must also be considered. Given the importance of caprock behaviour in this context, several previously published geomechanical caprock studies of depleted hydrocarbon reservoirs are identified and reviewed, comprising experimental and numerical studies of fourteen CCS pilot sites in depleted hydrocarbon reservoirs, in seven countries (Algeria, Australia, Finland, France, Germany, Netherlands, Norway, UK). Particular emphasis is placed on the amount and types of data collected, the mathematical methods and codes used to conduct geomechanical analysis, and the relationship between geomechanical aspects and public perception. Sound geomechanical assessment, acting to help minimise operational and financial/liability risks, and the careful recognition of the impact of public perception are two key factors that can contribute to the development of a successful CCS project in a depleted hydrocarbon reservoir

Συγκριτική διερεύνηση ενισχύσεων διώροφης κατασκευής απο οπλισμένο σκυρόδεμα ως προς τη βελτίωση της σεισμικής συμπεριφοράς

401 σ.Βασιλική Γ. Τσαπαρλ

Caprock integrity and public perception studies of carbon storage in depleted hydrocarbon reservoirs

Capture and subsurface storage of CO2 is widely viewed as being a necessary component of any strategy to minimise and control the continued increase in average global temperatures. Existing oil and gas reservoirs can be re-used for carbon storage, providing a substantial fraction of the vast amounts of subsurface storage space that will be required for the implementation of carbon storage at an industrial scale. Carbon capture and storage (CCS) in depleted reservoirs aims to ensure subsurface containment, both to satisfy safety considerations, and to provide confidence that the containment will continue over the necessary timescales. Other technical issues that need to be addressed include the risk of unintended subsurface events, such as induced seismicity. Minimisation of these risks is key to building confidence in CCS technology, both in relation to financing/liability, and the development and maintenance of public acceptance. These factors may be of particular importance with regard to CCS projects involving depleted hydrocarbon reservoirs, where the mechanical effects of production activities must also be considered. Given the importance of caprock behaviour in this context, several previously published geomechanical caprock studies of depleted hydrocarbon reservoirs are identified and reviewed, comprising experimental and numerical studies of fourteen CCS pilot sites in depleted hydrocarbon reservoirs, in seven countries (Algeria, Australia, Finland, France, Germany, Netherlands, Norway, UK). Particular emphasis is placed on the amount and types of data collected, the mathematical methods and codes used to conduct geomechanical analysis, and the relationship between geomechanical aspects and public perception. Sound geomechanical assessment, acting to help minimise operational and financial/liability risks, and the careful recognition of the impact of public perception are two key factors that can contribute to the development of a successful CCS project in a depleted hydrocarbon reservoir.</p