Numerical Simulation On The Behavior Of Lime-Soil Cushion Of CFG Pile Composite Foundation In Loess Areas

The CFG (Cement Fly-ash Gravel) pile is a pile with high bond strength and composed of cement, fly-ash, gravel, stone chips, sand and water. The CFG pile together with soil and cushion can better develop the bearing capatity of soil and reinforcement, further increase the bearing capacity of foundation, decrease settlement and get better economic benifits. However, the theory and design method of CFG pile composite foundation have not been well developed and the behavior and mechanism of CFG pile composite foundation have not been well studied, especially for the behavior of lime-soil cushion of CFG pile composite foundation in loess areas. Therefore, the further research on the behavior of CFG pile composite foundation has significant meanings for engineering use. The numerical software-ANSYS was used in this paper to study the effect of cohesion, friction angle, deformation modulus, thickness and load of lime-soil cushion on the behavior of composite foundation. As compared with the traditional gravel cushion, the conclusions can be drawn out as follows.(1) The CFG composite foundation with lime-soil cushion or gravel cushion has the same stress relationship with depth along the pile body. The maximum stress was not located at the head of the pile, but at a certain depth below the head of pile. The stress along the pile body was increased with depths when located above the maximum stress depth point while decreased with depths when located below the maximum stress depth point. At the initial stage of loading, the load was mainly carried by the soil. With the increase of the penetration of pile head, the stess ratios of pile to soil increased and the effect of piles has become more and more significant.(2) With the increase of cohesion, friction angle and deformation modulus of lime-soil cushion, the settlement and stress of pile head and the sress ratios of pile to soil increased while the penetration decreased.(3) With the increase of thickness of lime-soil cushion, the settlement and stress of pile head and the sress ratios of pile to soil decreased while the penetration increased. The critical thickness of cushion was 300mm. The suggestion thickness of lime-soil was given in this paper whick refers to 150mm to 300mm.(4) With the increase of vertical load, the penetration, settlement and stress of pile head all increased and the stress ratios of pile to soil increased first and then became stable.(5) The gravel cushion composite foundation with the same parameters as lime-soil cushion composite foundation except for cohesion was also simulated for the comparison purpose. It was found that the settlement and stressof pile head and stress ratios of pile to soil all increased while the penetration decreased.