Study On Optimum Design Of Gravel-Pile Composite Foundation

The soft soil foundation treatment with gravel pile is the one of most common method for the highway construction in China.There are many discussion on it theory,but its bearing mechanism keep the stage of semi-empiricaland calculation theory is not imperfect, especially the research on determination of pile-soil stress ratio need deep further.Through the consulting the related literature and data, bearing mechanism of gravel-pile composite foundation was analyzed. The distribution of additional stress and displacement change of single-pile composite foundation for rigid foundation was calculated by the software of ANSYS. And the additional stress and pile-soil stress ratio of pile group arranged at square for rigid foundation was calculated too. At same time this paper calculate the cases of gravel pile arranged at quincunx for flexible foundation, for example the additional stress of pile body, the distribution of additional stress between pile and soil, the influence of load level and modulus ratio between pile and soil on stress at top of pile and bearing rate of pile body, pile-soil stress ratio of pile group. The calculation and analysis provide the reasonable design reference for the design of gravel-pile composite foundation.The result show that the additional stress have a stress concentration for single-pile composite foundation. The pile-soil stress ratio can reach 2.29-4.15 and decrease with the increasing of depth. There is a effective pile length in the process of load transfer,which is as wall as the a stress concentration of foundation. For pile group at the rigid foundation, there a different stress concentration from the single-pile. And the axial force of pile shaft and pile-soil stress ratio along the depth is different with the single-pile, too. At the same soil and exterior load, the settlement of pile group is larger than that of the single-pile, but the maximum lateral deformation of group pile body is less than that of single-pile.For flexible foundation, the additional stress of pile-body decrease from the center line of embankment to slope.There is a same attenuation law for the additional stress of pile-body and pile-soil. The vertical stress at the top of pile and bearing rate of pile-body increase with the increasing of load and pile-soil stress ratio. The pile-soil stress ratio increase with increasing the load and area replacement ratio, but it will decrease after the peak. With it increasing, the pile-soil stress ratio has a linear growth.Based on analysis about bearing mechanism and the influencing factors of pile-soil stress ratio, the optimization design theory using the principle of conctroling basement subsidence is put forward for gravel-pile composite foundation. And this paper proposes that taking design load of foundation as calculation load of basement subsidence. At same time, design process and steps are introduced in detail.Finally, construction technology and quality control for gravel-pile composite foundation are introduced, which an provide the reference for similar project construction...