Experimental study on ptc pile composite foundation with cap in treating expressway soft soil ground

When cement-soil piles are applied to treat deep soft soil foundation of expressway especially in bridge head section, it is often showed insufficient ability in solving bridge-head jumping problems. In order to increase the pile spacing and decrease cost, the cement-soil piles can be replaced by prestressed tenssion cememt pile(PTC) with cap, which can make full use of the high bearing capacity of the PTC pile.The cap makes the deformation law of the foundation much different from which without cap or cement-soil pile foundation. Based on field test pile and loading experiments, the composite foundation treated by PTC piles with different treatment depth and cushion style is studied. It includes the settlement law in different depth, the differential settlement between the pile and the soil, the contiuous settlement law along the embankment cross section. Experiment and analysis results indicate that, For the effect of the cap and the cushion, the deformation of the reinforced area are more integrated, the stab deformation of the pile with cap was less than 10mm, the pile-soil stress ratio were adjusted efficiently. The variation law of the settlement along cross section presented wave form with little range of the peak and valley values. The variation range of the differential settlement is less than 15mm. The settlement of the substratum can be calculated by the layer-wise summation method, which can meet the request of soft soil ground improvement to the expressway engineering.