Measuring effects of X-section pile installation in soft clay

Cast-in-place concrete piles with an X-shaped cross-section (referred to as XCC piles) have been widely used in China for pile foundations and pile-supported embankments over soft ground. The lack of field measurements and methods of calculation for the effect of the pile cross-sectional shape on pile installation in clay led to the launch of an experimental programme in Nanjing, China. As part of the programme, in the present study the behaviour of the displacements and stresses measured in the vicinity of an XCC pile during its installation in soft ground was studied. A modified cavity expansion method suitable for use with an XCC pile was developed. The field measurements were compared with those calculated using the proposed method and the conventional cavity expansion method. The predicted maximum radial displacement, pore pressures and radial stresses were found to be in reasonable agreement with the field measurements. It was also shown that the effect of the installation of an XCC pile is similar to that of a circular pile, and the radius of XCC pile can be replaced by the radius of an (equivalent) circular pile that gives the same cross-sectional area.