The CGSE will have four geotechnical science themes, each of which will be linked to advanced computational modelling, state-of-the-art physical modelling and laboratory testing, and engineering applications (see Fig. 1). These fundamental science themes are described below.
The complexity in the behaviour of geomaterials is largely attributable to their granular nature and the presence of internal structure and multiple phases (solid, liquid and gas), as well as the marked influence of stress level and history.
Key innovations, involving all the nodes, will include the formulation of new models for highly compressible soft soils, as found on seabeds and in estuarine deposits, as well as novel ground improvement methods such as vacuum consolidation. Challenging aspects to be pursued will include the unresolved problems of creep and thixotropy in geomaterials, the role of damage at the macro and micro-scales under static and cyclic loading, the fundamental mechanisms that govern rate-dependent behaviour, the mechanical response at ultra low effective stresses (crossing the solid-fluid boundary and linking, for example, with scour), and the micromechanical origins of cyclic instability. These mechanisms govern the life-cycle response of heavy haul road pavements and cyclically-loaded foundations.
Emerging geotechnical design problems span material behaviour beyond the domain of conventional soil mechanics. This behaviour is often governed by multiphysical processes that operate at different length and time scales. Examples include submarine slides, where geomaterials at high water content may transform into non-Newtonian fluids, and the influence of gas which can alter the response radically. Similarly, the frictional strength of soil-structure interfaces depends crucially on the contact micromechanics, varying by an order of magnitude with loading rate and accumulated displacement.
Key innovations in this Program will address the multi-faceted behaviour of geomaterials, developing thermodynamically-sound multiphase models and efficient computational algorithms for solving complex problems including soft seabed sediments and highly compressible estuarine clays, coupled thermo-hydro-mechanical phenomena, and dissociation of gas hydrates. Sophisticated physical modelling, with visualisation of the deformation modes, will underpin the development of advanced computational algorithms for capturing the multi-phase material response. This synergy, which harnesses the strengths of the various geotechnical groups, is a major feature of the proposed CGSE and will be used across all the research Programs.
Current best-practice in geotechnical design is focused on stationary systems and constant material properties, aiming to attain negligible movement under working loads. However, many new infrastructure applications require an entirely new design paradigm which allows the geostructure to move large distances during its design life. Important examples include submarine pipelines on soft sediments, dynamic anchor installations in seabeds, installation of displacement piles, penetrometers used to measure geotechnical properties of soils, and foundations on soft clays.
Key innovations in this Program will include new analysis techniques that account for large deformations, soil-fluid-structure interaction, episodes of cyclic loading (and intervening recovery) and complicated interface behaviour. All three nodes in the CGSE have strong backgrounds in modelling complex boundary value problems, and will contribute to the development of novel techniques to simulate these phenomena. Moreover, the predictions from the advanced computational models will be compared against real behaviour observed in state-of-the-art physical modelling and field testing.
In response to industry and community demands, the modelling and management of geotechnical risk has become a major issue in the design of all forms of physical infrastructure. Indeed, the natural variability in geological deposits, coupled with the existing uncertainty in loading conditions and limited on-site data, make this a very challenging aspect for government authorities and engineering practice. There is a compelling case to extend traditional deterministic design procedures to a stochastic framework (Baecher and Christian 2003).
Key innovations in this Program will include the development of new stochastic limit and shakedown analysis techniques to predict the load capacity of geostructures under static and cyclic loads, new methods for the stochastic modelling of wave-structure-soil interaction with application to offshore production rigs, and risk-based prediction of slope stability and landslides and their effect on onshore and seabed infrastructure (such as pipelines). The Program will draw on the numerical modelling strengths of the Newcastle node, the centrifuge and constitutive modelling expertise of the UWA node, the extensive cyclic loading knowledge of the Wollongong node, and the probabilistic modelling expertise of PI Griffiths at Colorado to provide a rational and complete treatment of this challenging topic.