ICE - Institution of Civil Engineers - Virtual Library

This paper describes the results of static compression and tension load tests performed on three-instrumented large-diameter continuous flight auger piles installed in Dublin Boulder Clay. The piles developed very high shaft resistance and, in contrast to piles driven into Boulder Clay that exhibit friction fatigue, the shaft distribution was uniform along the pile shaft. This resulted in the normalised average shear resistance being mobilised by a bored pile exceeding that of a pile driven in similar ground conditions. In contrast, the base resistance of the test piles was significantly lower than that of a pile driven in similar ground conditions.

Dam core cracking is responsible for the initiation of piping in many dam incidents. Filters capable of controlling the concentrated leak through a cracked core are relied on to prevent internal erosion. The no-erosion filter (NEF) test, widely used for filter substantiation, is predicated on the assumption that all the base soils sustain cracks in their volume, and critical filters should be designed to control a concentrated leak. This study is aimed at finding some of the soils that self-heal and collapse owing to wetting. Self-healing soils cannot withstand cracks upon flooding, thus negating the feasibility of the NEF test for such soils. A comprehensive testing strategy is introduced for the recognition of self-healing soils. The results reveal that soils containing less than 15% fines content will not sustain cracks, and the possible cracks formed will self-heal upon flooding.

The ground remains the greatest source of risk to construction projects. In spite of a wealth of freely available information and guidance on the central importance of adequate site investigation in managing ground risk, many clients remain unnecessarily exposed to risk due to inadequate site investigation. The Federation of Piling Specialists undertook a comprehensive survey of geotechnical designers within its membership to evaluate the usefulness of site investigation information routinely provided to them. For nearly a third of all the piling and specialist geotechnical contracts surveyed, the site investigation information provided was poor, preventing optimisation of the foundation solution. The cost to clients arising out of poor site investigations far exceeds the savings that could be made by following good practice when investing in a site investigation. The survey indicates that good practice guidance is not being followed, resulting in investigations that are not adequately designed, specified or supervised.

The design and specification of a landfill clay liner require compromises to be made between the requirements of low hydraulic conductivity (permeability), adequate shear strength, sufficient interface shear strength (when the clay is used in a composite liner), minimal shrinkage during service, and sufficient ductility to accommodate tensile and shear strains, which may increase permeability. This paper focuses mainly on the first three requirements. The results of construction quality assurance (CQA) from four landfill sites and the results of ground investigations from two landfill site extensions are reported. Proposals are made for a methodology to derive a specification, and for assessing the results of CQA tests. Undrained and effective stress strength parameters are presented for recompacted Lias Clay. The interface shear strength of clay against a geomembrane or geotextile is shown to be dependent upon the density and moisture content of the clay and normal pressure.

The buttress wall is an alternative construction method for protection of adjacent buildings during excavation. It is generally recognised, but not verified, that the method has good effects in reducing wall movement and ground settlement, because buttress walls behave as T-shaped concrete beams, which possess comparatively larger stiffness than two-dimensional diaphragm walls. However, the behaviour of buttress walls in excavations is not fully understood, because of a lack of well-monitored case histories and systematic studies. In this study, the effectiveness of buttress walls in reducing wall deflection and ground settlement is evaluated through observed behaviour of a case history, and through finite element studies. The case study indicates that the use of buttress walls in a deep excavation can significantly reduce the deflection of a diaphragm wall. Effective prediction of the behaviour of the buttress wall can be achieved using the three-dimensional finite element method. Parametric studies reveal that deflection of the diaphragm wall is strongly influenced by the condition of the restraint at the bottom of the buttress walls, and by the number of buttress walls. As long as the buttress wall bottom is well restrained, and reasonable numbers of buttress walls are installed, wall deflection can be considerably reduced.