Study of influence of cushion on settlement of cement-soil mixing pile composite foundation

The influence of cushion thickness on the settlement of cement-soil mixing pile composite foundation was studied by the static load tests and numerical simulation. The static load tests of natural foundation and four cement-soil mixing pile composite foundations in which the cushion thickness was different were carried out for the silt soil in Zhuhai area. The settlement-tubes and magnetic rings were pre-buried in the foundation. And the probe with scale was used to detect the positions of the magnetic rings and obtain the data of the layered settlements. According to these experimental data of composite foundation for four cement-soil mixing piles, the settlement law was analyzed; and layered settlements of piles and soil in different composite foundation were calculated by numerical calculation. The comparison between the different composite foundation shows that the settlement of pile could be reduced by the cushion, but the thickness of cushion has a significant influence on the supporting capacity of composite foundation -a much thicker cushion could weaken the supporting capacity and increase the settlement of composite foundation. For choosing the optimal thickness of cushion, the geological condition was suggested to be considered except for the supporting capacity and settlement of composite foundation. The cushion thickness could be from 20 cm to 40 cm -the higher value is selected when the silt layer is below the middle sector of pile, conversely the lower value is selected.