Study On Characteristic Of The Pile-Soil Slipping Work In Soft Soil

Because of so many advantages, piles are now widely used in soft soil in civil engineering during the construction of cities. But till now, the theory of pile analysis can't exactly simulate the mechanism and relation of the embedded pile. Considering that at present when the theory of elasticity is used to calculate the displacements of pile and soil in vertical load, we usually assume that the displacements of pile and soil are synchronal. But in fact, the displacements of pile and soil can't be completely consistent, they exist slipping, and when the relative displacements reach one ultimate value, continue increasing the slipping, the pile skin friction will not increased synchronizing, so the calculation and reality have wider difference. The assumption can't use in practice. On the basis of the work available, the author has further studied the characteristic of the pile-soil slipping work in soft soil. The main work includes:Firstly, based on the elastic theory, through discretization of single pile and soil in homogeneous elastic half-space, using Mindlin's displacement solution, a function relationship of soil's displacement and skin friction is made. Then the displacement differential equation of single pile is deflated by the finite difference method. Through this, a governing equation of pile displacement and skin friction is developed. The two parts can establish connection by displacement coordination relationship. This method considers the continuity of soil, owns rigid theory, the discreteness of calculation is very small, it has extensive developing future.Secondly, using elastic-plasticity constitutive model on contact surface of pile and soil, the parameters are studied. Then according to the choosing skin resistance model, the analytical method is represent when there exist slipping but no ultimate relative displacement and the foundation is homogeneous. The settlement of surrounding soilcan be calculated by ML method which considers the effect of the soil modulus at all soil layers. On the analysis of slipping, the paper focuses on the settlement analytical method when the pile is embedded in multi-layered foundation. In the end, through one case study, it calculates the pile settlement in four different situations, and a comparison analysis is made between calculation and static test. Through this, the performance of the various analytical methods is reflected, and some conclusion can be drawn.Thirdly, for the pile embedded in soft soil, the production mechanism, condition and the usual method of cancelling the influence of the negative skin friction are stated. Then it emphasizes on the research of negative skin friction under a uniform surcharge. In this part, the total settlements of soil consist of consolidating settlement and compressing settlement: the consolidating settlement may be computed by using Terzaghi's one-dimensional consolidation theory; the compressing settlement is expressed by using Mindlin's displacement solution. And the settlement of pile can establish connection with the skin friction by the finite difference method. According to the choosing skin resistance model, firstly it assumes that there has slipping but no ultimate relative displacement, the distribution of skin friction is analyzed while the soil is homogeneous or multi-layered, then it consider that there exists ultimate relative displacement, and continue the same analysis. With the calculation and static test in various conditions, some conclusion can be drawn.Finally, the paper is summarized. Certain problems which need more research are explained generalized, and some proposals are advised.