Study On Design And Computation Method Of Geosynthetic Reinforced Pile-Supported Embankments

Pile-supported reinforced embankment is a new type of ground improvement technology. It has some distinctive merits in rapid construction rate, short construction time, unnecessary of preloading and additional excavation, effective control of ground settlements and lateral displacements, and basically the same construction cost as conventional soil cement mixing piles, etc. It offers an economical and effective solving method for the construction of roads, dams, retaining walls, and oil silos on soft grounds. The extents and realm of its applications are increasingly expanding, particularly to the highway projects where the rapid construction is required and the settlement is seriously controlled. The working mechanism of the pile-supported reinforced embankment is very complicated, and hence the research works are lagged behind. Currently there is no design method and specification in our country. Its design depends mainly on the compound ground theory and the practical experiences, sometimes leading to inconsistent results with the reality. This has an influence on the scientific applications, and hence restricts its applications.This dissertation analyses the global force system of the pile-supported reinforced embankment, which is composed of filled materials, reinforced cushion, pile and pile cap, soils in-between piles, and soils underlying piles. The analyzing models and the governing equations were established for the soil arching effect of the filled materials, the uplifting effect of the reinforced cushion, the frictional effect of the pile-soil interaction, the supporting effect of the pile-end bearing layer. With the boundary conditions of stress continuity and strain compatibility, the global analyzing model and the simultaneous equation groups were obtained. Also obtained were the calculation methods for the pile-soil settlement, load sharing ratio, tension force of the reinforcement, elevation of equal settlement plane, axial force and skin friction of the piles, etc. MATLAB package was used to code a program in window form for rapidly and conveniently solving the simultaneous equations.By a large amount of computations with the established analyzing model and coded program, the parametric influences were systematically analysed for the pile-supported reinforced embankment, such as the settlements and settlement differences of the piles and the soils in-between piles, the elevation of the equal settlement plane of the embankment, the load sharing ratio of the piles, the tensionforce of the reinforcement, the location of the neutral point, and the depth of the equal settlement plane of the bearing layer, etc. Further investigated is the mechanical behavior of the interactions of the composed parts of the pile-supported reinforced embankment.Three typical sections of the pile-supported reinforced embankments of a highway were selected for the field tests with the stress and strain instruments buried. By a large number of field measurements, the variation patterns with the placed load and the observation time were obtained for the settlements, the load sharing, and the axial forces of the piles. Numerical analyses were also carried out for two typical tested sections using the FLAC software. Calculated results were obtained for the settlements, load sharing, the stresses and strains of the horizontal reinforcement, and the axial forces and skin frictions of the piles. Results from the analyzing model, the field tests and the numerical analyses were compared. It verifies that the analyzing model is capable of reflecting the real working behavior of the pile-supported reinforced embankment. The calculated results are reliable and applicable to the engineering practice.Finally, from the point view of the design of the practical engineering, the design routine and its application extents were investigated. The design methods were proposed for the reinforced cushion, the pile cap, and the pile layout of the pile-supported reinforced embankment. Also proposed were the calculation methods for the settlements, the bearing capacity and the global stability. These made up of a set of practical methods for the analyses and calculation of the pile-supported reinforced embankment. They have also been included into the Technical Guide of the Design and Construction of Roads on Soft Soils, which is a standard of the Ministry of Transportation.