Dynamics Research Group

Projects

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Research Areas

Earthquake Engineering Research Centre

Earthquake engineering is concerned with the design and construction of all kinds of civil and uilding engineering systems to withstand earthquake shaking. Earthquake engineers, in the course of their work, are faced with many uncertainties and must use sound engineering judgement to develop safe solutions to challenging problems. They also rely heavily on state-of-the-art techniques in computing, materials science, laboratory testing and field monitoring.

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Structural Performance

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Integrity of Nonlinear Dynamic Structural Systems

The performance and safety of many civil engineering systems is governed by their response to dynamic loads such as earthquake, wind and traffic. However, there is very little work on the robustness of structures under dynamic loads. In fact, robustness is not well understood even under static loads. Concepts and methods have been developed to investigate the vulnerability and integrity of non-linear dynamic structural systems. The method involves modelling structures at different levels of definition. Representative finite element simulations are used to generate low-dimensional models which are suited for multiple simulations to identify dependable regimes in the space of control parameters. Proper Orthogonal Decomposition forms a useful basis for the reconstruction of such models and the identification of vulnerable members. Example studies demonstrate that the output from such studies will be of practical use for the safety management of structures under dynamic loads.

Dynamic torsional behaviour of geomaterials

Equipment for combined axial and torsional dynamic loading of geomateral is being developed jointly with the Earthquake Engineering Research Centre. Hollow cylindrical samples can be subjected to combinations of internal and external pressure, axial load and torque so that the dynamic properties can be studied under complex states of stress with real time closed loop control at rates of up to about 100 Hz.

Multi-axial behaviour of sand

The behaviour of sand under 3D states of stress is being explored using two multiaxial devices: a rigid-boundary True Triaxial Apparautus and a flexible-boundary Cubical Cell. Samples are subjected to complex stress paths, and the results will be used to calibrate kinematic hardening models that can capture the response to complex non-monotonic loading. Piezo-ceramic bender/extender elements are being used in the Cubical Cell to acquire full sets of elastic stiffness parameters.

Behaviour of fibre-reinforced sands

Research is being initiated on the laboratory behaviour of fibre-reinforced sands. A fundamental study of the effects of fibre inclusion on the strength and stiffness of sands will, it is hoped, lead to the wider application of this technique in highway embankment construction. There is also the possibility that fibres will inhibit liquefaction of saturated granular deposits and their inclusion in tailings for this purpose seems promising.

Modelling of clay slopes

Recent geomorphological research on coastal cliff degradation at Walton-on-the Naze included development of a numerical model for London clay within the FLAC platform. It proved possible to model the combined effects of swelling and strain softening and changes of geometry due to toe erosion. In conjunction with colleagues in the Department of Geographical sciences and colleagues at the University of Newcastle, this work is now being extended to the modelling of a vegetated clay embankment to be constructed from London clay and instrumented.

Constitutive modelling of sand and destructuration of natural clay

Constitutive models for sand under non- monotonic loading are being used to model the dynamic behaviour of foundations on the shaking table. The Brick model has been calibrated against cyclic simple shear tests; kinematic hardening models which link strength, density and stress level are being developed with the universities of Birmingham and Trento. Plastic straining leads to breakdown of structure of natural clays. A model for this process is being developed within a kinematic hardening framework. As the destructuration continues the soil behaves in the same way as reconstituted soils.

Modelling of creep consolidation of soft clays

Following field observations of the behaviour of embankments constructed over soft clay for the M4 and M49 approach motorways to the Second Severn Crossing, a visco-elsatic plastic finite difference model has been developed to analyse the consolidation of soft clay around vertical drains. The analysis incorporates the effects of creep, smear and drain resistance. It is applicable to problems involving both embankments on soft clay and large scale reclamation. It is currently being used to predict and back-analyse the behaviour of soft clay beneath the Escravos reclamation project in eastern Nigeria.

Soil/structure interaction in deep basements

Field monitoring of multi-propped excavations constructed in Gault clay and in Taipei by top-down methods has provided a wealth of data. Back-analysis has shown the importance of non-linear stiffness in controlling the deformations both during diaphragm wall installation and main excavation, and that the soil response was not fully undrained.

Sand-steel interface friction

Fundamental studies of sand-steel interfaces have been carried out in the laboratory using a modified direct shear apparatus. The effects on interface friction of surface roughness, particle size, sand density and stress level have all been systematically studied. A clearer picture is emerging of the role of dilation in understanding peak and post-peak strength.

Observational geotechnical design

Generic models of the process of observational design are being developed both to provide tools with which organisation and decision making structures can be recorded and to assist in the effective operation of observation projects.