Analytical and numerical investigation of soil arching effect of the composite foundation reinforced by penetrated PCCSs and partially penetrated DM columns under embankment loading

The development of innovative and cost-effective pile-supported embankment technologies is an intrinsic demand driving the advancement of soft ground improvement techniques. A significant innovation within this approach is the penetrated precast concrete pile reinforced with cemented soil (PCCS) combined with partially penetrated deep mixing (DM) columns for layered ground treatment, in which the PCCS is created by embedding a precast concrete (cored) pile within a DM column. This study aims to develop a numerical unit model for this type of pile-supported embankment, denoted as a PCCS multi-pile composite foundation-supported embankment, providing insights into the soil arching effect within the embankment and elucidating the variation patterns of vertical stress and the horizontal earth pressure coefficient along the embankment height. Based on Hewlett’s hemispherical arch model, a refined composite soil-arching analytical model is proposed specifically for the multi-pile composite foundation-supported embankment. The findings reveal that the critical height of the embankment is 1.05 times the net pile spacing, with embankment height showing minimal influence on the height of internal and external arches. In contrast, an increase in the embankment filling modulus significantly affects the fan-shaped arches between adjacent piles, while its impact on spherical arches remains limited. The stress ratios between the PCCS-soil and DM column-soil derived from the three-dimensional composite arch model differ from the measured results by 7.3 % and 8.5 %, respectively, confirming the model’s accuracy.