Research On Behavior Of Driven Cast-in-place Tubular Pile Composite Foundation Under The Road Embankment Loading

With the fast development of the national economy, more and more highway is constructed on thick soft clay ground. As a new foundation treatment technique, driven cast-in-place tubular pile (DCTP) combine both advantages of pre-stressed tubular pile and buffeting-sunk pile, and have the properties of less concrete quantity, low cost, high bearing capacity and suitable for construction. Therefore, it has a good application perspective in soft clay ground treatment. Theoretical study of the DCTP and the DCTP composite foundation below the embankment is carried out in this thesis.First, DCTP is introduced briefly. A general analysis of the current pile foundation and composite foundation theory is followed.Secondly, in-situ experimentation of DCTP soft clay treatment located in bridgehead is introduced. Results obtained are analyzed, specifically include: pile quality, test of the bearing capacity of single-pile and multi-piles, variation of ground property before and after pile construction, top and pile-to-pile soil pressure, delamination settlement, horizontal displacement and pore water pressure observation. Results show that craftwork for DCTP is applicable, and construction quality is tenable. In addition, it is found that DCTP combining the geogrid to perform bridgehead soft ground treatment is able to solve the car-jump problem.Thirdly, pile-ground interface friction touch is considered. Axis-symmetrical in-plane finite element method is used to perform numerical simulation of single DCTP under vertical loading. The inner and outer friction forces of DCTP, pile-end resistance force and variation of loading share ratio and performance of soil plug are analyzed. A formulation to perform computation of single pile utmost bearing capacity is proposed.Fourthly, DCTP composite foundation is simulated using typical three-dimensional finite element model. Pile-ground interface friction touch, geogrid of underlayer and layered loading of earthfilling is considered, so that the computational model is morerational. The deformation of composite foundation and the basic principle of influential factors on the load transformation are also studied. It is found that most part of the load is undertaken by the pile due to the soil arching effect in embankment soil, tensioned membrane effect in geogrid or beam effect in multi-layer grid underlayer. Thus, the total settlement and uneven settlement of the composite foundation is reduced effectively.Lastly, the numerical results obtained by finite element analysis are compared with those obtained by in-situ experimentation. Results show that performance analysis of the single DCTP and under embankment DCTP composite foundation using finite element method is applicable.