DEVELOPMENT OF MULTI-ANCHOR EARTH RETENTION SYSTEMS.

This paper discusses two projects, the first relating to tests on 'reinforced earth' conducted on the 1. 5 m radius centrifuge at U. M. I. S. T. and the second concerning a short pilot study on the T. R. R. L concept of 'anchored earth' carried out on the 5 m radius Cambridge Geotechnical Centrifuge. The paper proposes a role for centrifugal model testing in design evaluation, whether by the designer himself, his centrification authority, a rival patent holder, or a research worker.

Hydrodynamic pressures behind flexible and rigid dams

During earthquakes, hydrodynamic pressures are generated by the impounded reservoir on the dam face. The magnitude and distribution of the hydrodynamic pressures vary with factors such as frequency and intensity of earthquake-induced ground motion, depth of impounded reservoir, stiffness of dam and geological conditions. It is difficult to obtain experimental data on hydrodynamic pressures from the field owing to uncertainties associated with earthquake loading. This paper aims at using dynamic centrifuge modelling to measure hydrodynamic pressures behind both relatively stiff and flexible model dams. Comparisons of the experimental data with theoretical hydrodynamic pressures show that Westergaard's equation gives a conservative estimation of hydrodynamic pressures. Comparison with Chopra's method revealed that it underpredicts hydrodynamic pressures for low reservoir depths but gives reasonably good predictions for higher depths of reservoir. It is concluded that dynamic centrifuge modelling may be an effective experimental method to estimate the hydrodynamic pressures acting on a dam. © 2010 Thomas Telford Ltd.

Fiber laser processing of amorphous rare earth NeFeB magnetic materials

Since the exchange coupling theory was proposed by Kneller and Hawig in 1991 there has been a significant effort within the magnetic materials community to enhance the performance of rare earth magnets by utilising nano-composite meta-materials. Inclusions of magnetically soft iron smaller than approximately 10 nm in diameter are exchange coupled to a surrounding magnetically hard Nd2Fe14B matrix and provide an enhanced saturisation magnetisation without reducing coercivity. For such a fine nanostructure to be produced, close control over the thermal history of the material is needed. A processing route which provides this is laser annealing from an amorphous alloy precursor. In the current work, relationships between laser parameters, thermal histories of laser processed amorphous stoichiometric NdFeB ribbons and the magnetic properties of the resulting nanocrystalline products have been determined with a view to applying the process to thick film nanocomposite magnet production.

Dynamic earth pressures and earth pressure cell measurements

Failure of retaining walls is observed after many recent seismic events. Design of these walls are based on the pseudo-static force designs based on the Mononobe-Okabe earth pressure coefficient equations. However, it is clear that there are limitations attached with this approach. This paper investigates the seismic behaviour of sheet pile retaining walls using dynamic centrifuge testing facilities. In addition to using bending moment strain gauges on the wall, new generation earth pressure cells have also been used to investigate the generation of active and passive earth pressures. The results indicate that Mononobe-Okabe equations give relatively good estimates of active earth pressures but may be over-predicting passive earth pressures at certain peak ground acceleration levels. Based on this series of centrifuge tests it is concluded that earth pressure cells are successful in providing good qualitative data, but need to be supplemented by good calibration methods. © 2010 Taylor & Francis Group, London.

Numerical modelling of hydrodynamic pressures on dams

This paper discusses several considerations related to appropriate numerical modelling of the reservoir hydrodynamic pressures on dams. The reservoir is modelled with 8-noded isoparametric displacement based solid finite elements. The study includes both stiff and flexible dams with vertical and sloped upstream faces under ramp, harmonic and random acceleration loads. The numerical results were compared and found to be in good agreement with available closed-form solutions. The same approach may be used in analyses of other waterfront structures such as quay walls. © 2013 Elsevier Ltd.