Experimental Study on Pile Load Transfer Considering Rice Stone Filled-In Gaps between Steel Drive Pipe and Pile Casing in Karst Region

Abstract

For a guarantee of perpendicularity and stiffness in piles in Karst areas, full rotary cast-in-place piles are often utilized, steel pipes are rotarily driven into a stratum, and inner-steel pile casing is positioned. With the engineering background of the bridge piles of Guinan high-speed railway in Guangxi autonomous region, the space between steel drive pipe is filled with rice stones, the load-transfer mechanism of which was studied. An apparatus was designed for pullout of the drive pipe, rice stones are replaced with coarse stones, a simplified organic glass-pipe model is put forward, another similar indoor stratigraphic model is also pre-cast, and the movement of coarse sands and load transfer is studied with two models. The quantity of sands is calculated using back analysis through reappearance and the Rhino model: the first one is estimated using a reproduction of the pullout procedure, the second is calculated through the Rhino model based on the observation of the shape of sand in caves. When the drive pipe is pulled out, some coarse sand flows into the Karst caves and becomes loose, while load is applied on the top of the pile. The movement of coarse sand develops further, and more coarse sand flows into caves close to the bottom; this leads to a reduction its frictional resistance, and the axial force of the pile increases closer to the upper position of the cave, whereas the axial force of the pile is concentrated almost constantly close to the bottom of the cave. Comparing the end resistance and the frictional resistance, coarse sand can bear pile load to a great extent.