Theory And Practice Of Thin-wall Pipe Pile Using Cast-in-situ Concrete

Thin-wall pipe pile using cast-in-situ concrete (simply named PCC) technique is a new ground improvement technology developed independently by Prof. Liu Han-long et. al. (Geotechnical Institute of Hohai University). This new pile style has advantages of prestressed pipe pile, buffeting pipe-sunk piles and buffeting mould-sunk cutoff wall. This new form of pile system is suit for soft areas with short construction time and easy operation. So it has great practical value and bright market prospect. As a new techniques, the load transfer mechanism for single PCC pile and performance of PCC pile composite foundation are still unknown. This status limited the more application and development of this method.Based on the former researcher's work, this thesis researched the question above via field experiment, laboratory test and theoretical analysis. The main contents of the current research are as follows:(1) A new pile style-PCC pile is developed. The principle, equipment, construction method, technical characteristic, applications and pile quality test method of PCC are introduced in detail.(2) Based on the tests in situ, the effect of compacted soil during PCC pile installation in clay is presented in the thesis. It is found that the soil plug is unplugged or partially-plugged during the pile driving. It is also shown that the PCC pile is a partially displacement or small displacement and the pile geometry is the key factor to control the effect of pile installation.(3) Using the Strain Path Method (SPM) and the Finite Element Method (FEM), the soil disturbances caused by the penetration of PCC pile is studied. The deformation and strain fields solved provide more realistic predictions than Cavity Expansion Methods utilized at present to estimate installation effects.(4) Field experiment study on PCC pile is introduced in detail in the thesis. The test content includes the problems that maybe occurred during construction in soft clay. The test program can guide similar projects.(5) The soil plug and pile are modeled as a series of masses and springs, a simplified method to estimate the load-settlement relation of PCC is proposed. In the method the interaction between the soil plug and the pile is considered. A parametric study bas been made by the simplified method, the results indicate the method is more convenient to be used in engineering design.(6) Load transfer is studied by means of a axisymmetric finite element elastoplastic model that includes interface elements for representing slippage , pile-soil separation and soil nonlinear behavior. Numerical results indicate that good agreement exists between the finite element prediction and the field test for the head load-settlement curve. Inner frictional resistance, outer shear stress, end bearing and effects of soil plug those can not be investigated by field test are studied in details. Inner frictional resistance along soil plug is described by exponent function,then the formula to compute the inner factional force and the ultimate load of PCC pile is proposed.(7) The results of FEM analysis show that due to the combination of embankment soil arching, tensioned membrane or stiffened platform of geogrid, and stress concentration due to the stiffness difference between pile and soil, a majority of road embankment loading is transferred to piles, then the settlements and differential settlements are reduced significantly. The main factors are also studied by numerical analysis.(8) The horizontal displacement of the composite ground improved by rigid piles is negligibly small, thus the only remaining component is vertical settlement. Equilibrium equations, geometry equations and physical equations are used to derive the governing equation of the problem. Boundary condition at the soil-pile interface is accounted at two different states: the displacement of the pile and the surrounding soil are compatibility or slippage is developed at the interface. The displacement of the pile and soil can be solved by finite difference method from the governing equation. Then sk...