Study Of Settlement Computation Method Of Composite Foundation Under Embankment

Composite foundation is widely used in construction projects. However, its settlement computation method needs improving. Recent researches are mainly aim at the composite foundation under rigid base. Only a few of the research results published are about the composite foundation under embankment or flexible load. When a highway is built on soft clay, vehicles will bounce when they run through a bridge approach because of large settlement difference between a bridge and embankment. The composite foundation under an embankment is not same as that under rigid base in that an embankment provides enough space for pile stabbing into and embankment weight is a kind of flexible load so that their pile-soil stress ratios would be different. As no flexible field load test has been developed, prototype observation and numerical analysis are reasonable way to study composite foundation under embankment. With a suggested displacement model, this dissertation takes the interaction of soil and piles into consideration and derives an analytical-function of compressive deformation of stabilized layer of composite foundation under embankment. Analytical-functions are also derived of frictional resistance between pile and soil and of the pile-soil stress ratio. One simple method for computing the deformation is also derived, based on the analytical-function of friction resistance.Since piles are set into a composite foundation under an embankment it can not be directly analyzed in the plane strain way. To compute its settlement, a representative segment method is developed and used in settlement analysis of composite foundation under embankment. Compared with the traditional plane strain method that needs to unreasonably suppose piles as walls, the representative segment method is more reasonable. This dissertation, by FEM and ABAQUS program, discusses the normalized compressive deformation of stabilized layer and sub-layer of a composite foundation under an embankment and produces fit formulas.Based on the numerical analysis, a settlement formula is suggested and pertinent adjustment coefficients are produced. Composite foundation settlement can be computed from the pertinent natural foundation deformation and the adjustment coefficients. A composite foundation under embankment is given to show how to use the representative segment method in computing its settlement.Jialichen Bridge uses a composite foundation of low strength piles with different length along embankment to reduce settlement difference between the bridge and embankment. This dissertation is an analysis of the field observation results, including pile-soil stress ratio, settlement of the piles and soil, settlement in different depth, lateral displacement and pore pressure. The prototype observation shows that because settlement of soil is larger than that of piles, "arch effect" appears in the embankment so that its weight is gradually transferred from the soil to piles and pile-soil stress ratio increases.Thanks to the composite foundation, two-thirds of natural foundation settlement is removed. It is more significant that embankment settlement is basically even because of the piles with different length along the embankment. The observation of settlement in different depth shows that larger deformation is produced in the layers nearby the stabilized layer bottom.