Development and optimisation of steel piled foundations

[Truncated abstract] Steel piles are used widely for piled foundations. Many findings about the behavioural mechanisms of piled foundations have been revealed through a variety of research, especially for tubular pipe piles. On the other hand, there has been much less research on other shapes of steel piles such as H-shaped and sheet piles. The differences in behaviour between these types of pile are attributable to the cross-sectional geometry, which is not closed as for tubular piles but is open-shaped. This difference leads to a weaker arching effect within the pile under vertical load. This research has addressed the effect of the cross-sectional shape of piles (i.e. 'shape effects') on the axial response of piles in sand with the aim of optimising pile foundation systems utilising a better understanding of the arching effect. A theoretical approach has been described using a new formulation to quantify shape effects taking into account vertical arching theory within the concave segment of an open section pile. A new parameter, termed the 'shape factor', has been proposed, incorporating the aspect ratio and the enclosed angle of the concave area of a pile. The proposed formulation shows that the stress level adjacent to a pile tends to rise exponentially with an increase in shape factor and depth below the ground surface. The enhanced stresses above the ambient conditions that are found around a pile due to shape effects were also verified by numerical analysis. To investigate shape effects and the resulting changes in pile capacity, more than 40 pile installation tests at 1-g and in the centrifuge were performed to give insight into the link between pile shape and many aspects of axial pile response. Different shapes of pile installed into sand were compared to measure installation resistance, compressive capacity and tensile capacity, demonstrating that penetration resistance in sand can be strongly affected by the cross sectional shape of piles. In addition, changes in the horizontal stresses acting on the pile have been measured using pressure sensors embedded on the pile shaft within a concave or enclosed area. The values measured for different shaped piles varied and increased with installation depth as well as increase of shape factor. A good correlation was identified between the stress amplification around the pile and the product of the shape factor and the depth – which was termed the arching strength, supporting the proposed theoretical estimation. Finally, the mechanism behind the arching effect has been discussed and proposed new formulae for shape effects described...