Now showing 1 - 5 of 5
  • Publication
    Shaft Capacity of Open-Ended Piles in Clay
    This paper describes an experimental investigation designed to assess the impact of pile end condition on the capacity of piles installed in soft clay. A series of field tests are described in which instrumented open-ended and closed-ended model piles were jacked into soft clay. The radial stresses, pore pressures, and load distribution were recorded throughout installation, equalization, and load-testing. Although the total stress and pore pressure developed during installation were related to the degree of soil plugging, the radial effective stress that controls the shaft resistance was shown to be independent of the mode of penetration. The long-term shaft capacity of the open-ended pile was closely comparable to that developed by closed-ended piles, suggesting a limited influence of end condition on the fully equalized shaft resistance. In contrast to the shaft resistance, the base capacity was highly dependent on the degree of plugging.
    Scopus© Citations 65  1590
  • Publication
    A field investigation of vertical footing response on sand
    (Institution of Civil Engineers/Thomas Telford Publishing, 2009-10) ; ;
    This paper presents the results from an experimental programme that studied the factors affecting the bearing resistance of shallow footings in sand. In particular, the tests considered the effects of the footing width and embedment depth on the pressure-settlement response. By comparing the results with field tests on full-scale footings, simple correlations between the bearing pressure mobilised at normalised settlement levels of 5% and 10% of the footing width and the Cone Penetration Test qc value were studied. These correlations were found to be independent of footing size, embedment depth and sand state, although they were affected by creep. The rate of mobilisation of the footing resistance at low settlements was found to be strongly dependent on the initial soil state and the previous loading history. A simple nonlinear elastic soil model was found to adequately predict this response.
    Scopus© Citations 31  2973
  • Publication
    Cyclic and Rapid Axial Load Tests on Displacement Piles in Soft Clay
    Offshore piles are subjected to complex loading regimes, which include both rapidly applied static and cyclic loads. This note describes an experimental investigation conducted in order to assess the factors influencing the response of offshore piles to these loading conditions. The tests were performed using instrumented model piles installed in soft clay. During cyclic loading, the piles demonstrated a transition from stable to unstable behaviour when the applied loads reached a specific load threshold. Stable behaviour was defined when increments of plastic displacement decreased as the number of load cycles increased. During stable behaviour, radial effective stresses at the pile-soil interface remained constant. During unstable behaviour, pore pressures at the pile-soil interface rose as the number of cycles increased. This resulted in reduced radial effective stresses and progressively increasing displacement rates. Due to the presence of these excess pore pressures, the shaft resistance recorded during static load tests, performed after a period of unstable cyclic loading, were lower than those measured on piles where the pore pressure was fully equalised. However, the axial resistance was seen to be rate dependent. Fast loading of the pile resulted in reductions of pore water pressure at the soil-pile interface and enhanced shaft resistance which could overcome the negative effect caused by cyclic loading.
    Scopus© Citations 6  1039
  • Publication
    Axial resistance of CFA piles in Dublin boulder clay
    (Institution of Civil Engineers/Thomas Telford Publishing, 2008-08) ; ;
    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 which 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 were significantly lower than a pile driven in similar ground conditions.
    Scopus© Citations 15  5113
  • Publication
    Field investigation of base resistance of pipe piles in clay
    (Institution of Civil Engineers, 2010-02-01) ; ;
    This paper presents the results of a series of field tests performed to study the effect of soil plugging during installation on the base resistance developed by an open-ended (pipe) pile in clay. Three instrumented pipe piles were installed in soft clay, and the installation resistance and soil plug development were recorded. The tests revealed that the annular base resistance was equal to the cone penetration test q c resistance and was independent of the soil plug development. In contrast, the soil plug resistance increased from a minimum when the pile was fully coring to a maximum when the pile was fully plugged. A simple expression is proposed that links the plug resistance to the cone penetration test q c value at the specified depth and the incremental filling ratio value developed during installation. This expression is shown to provide reasonable estimates of the plug resistance developed by a large-diameter pipe pile driven into stiff to hard clay in the North Sea. The proposed relationship will be particularly useful for modelling the installation resistance of monopile foundations.
    Scopus© Citations 26  1103