Study On Deformation Of Tamped Cement-soil Pile Composite Foundation Under Embankment

With the pile composite foundation more and more applied in soft foundation treatment of highways, it is found that behaviors of pile composite foundation in flexible foundation is greatly different from those of pile composite foundation under the bearing platform, and the theoretical value of both the strength and settlement of the composite foundation shows noticeable difference from the actual value. In view of the tamped cement-soil pile composite foundation applied in the highway soft ground for the first time in Hebei province, using theoretical analysis, finite element simulation and the field test, the deformation behavior of the tamped cement-soil pile composite foundation is researched, providing a more scientific technical basis for the design and computation of the tamped cement-soil pile composite foundation.First of all, based on the flexible pile composite foundation's model supposition, the load transmission mechanism and the deformation pattern of tamped cement-soil pile composite foundation is analyzed. According to stress analysis of the equivalent cell in pile composite foundation under flexible foundation, and based on the pile composite foundation's deformation coordination condition and the static balance condition, the stress distribution in the pile and soil as well as the change of the pile-soil stress ratio is discussed.Secondly, with the aid of finite element simulation technology, using non-linear finite element software, many factors which influence the deformation characteristic of tamped cement-soil pile composite foundation are analyzed in detail, such as the cushion modulus, the pile modulus, the foundation soil modulus, the pile spacing (displacement ratio), the subgrade modulus, the height of subgrade and length to diameter ratio. The primary factors that should be considered to control the deformation of composite foundation are proposed.Taking Baoding-Cangzhou expressway as an example for the use of tamped cement-soil pile in reinforcing the soft ground, bearing and deformation characters of tamped cement-soil pile composite foundation under embankment load are analyzed through field test monitoring, and ground deformation characteristic and settlement law are studied. In view of characteristics of tamped cement-soil pile composite foundation, the deformation character as well as law of tamped cement-soil pile composite foundation is calculated and analyzed through finite element model. Comparing the field tests with finite element calculation results, it can be found that the stress and deformation test results of tamped cement-soil pile composite foundation are discrete due to the influence of construction factors, but the trend of changes is similar to the calculation results, thus proving the reliability of finite element method, which provides technical reference for studying the character of tamped cement-soil pile composite foundation under embankment load.