| With the rapid economical development, China has undergone a massive development in transportation infrastructure in recent years. Many highways and railways have been constructed. However, weak ground soils (for example, highly compressible soft soil, alluvial clay, peat, etc) are inevitably encountered in engineering practice. Geosynthetic-reinforced and pile-supported (GRPS) embankment is wildly used in the above-mentioned infrastructures due to its short construction period and low costs. However, with increasing application of the conventional technique of GRPS embankment (named CT embankment), many problems are exposed (i.e., intolerable total or differential settlements, large lateral displacement, global or local instability, low efficiency of geosynthetic, etc). To solve these problems, a new ground improvement technique referred to as the fixed geosynthetic technique of GRPS embankment (named FGT embankment) is proposed. For further and better understanding this new technique, the theoretical analysis, field test and numerical analysis are employed to study the performance of FGT embankment in this dissertation, respectively, and the main contents are presented as follows:(1) In view of those deficiencies of CT embankment, the FGT embankment is developed in this study. The principles and construction techniques involved in the FGT embankment are described firstly. Then, the numerical analysis method and two-stage analysis method are used to study the performance of FGT embankment, respectively. The results show that the FGT embankment can reduce the total and differential settlements, and promote efficient load transfer from the subsoil to piles significantly.(2) To distribute the differential settlement between a bridge and adjacent backfill embankment over a longer transition zone, three techniques (a) the FGT embankment,(b) the CT embankment, and (c) geosynthetic-reinforced embankment without piles are used at the same trial bridge approach site, which is located at the east of MCK+826No.0Bridge in Shanxi Province, the central region of China. The variation of the settlements, the lateral displacements, the pressures at the top and bottom of the geosynthetic layer and the strains of the geosynthetic layer with the increase of the embankment height between the FGT and CT embankments are investigated by field tests. The results show that the settlements and lateral displacements in the CT embankment are larger than those in the FGT embankment. The differences of settlement and lateral displacement between the FGT and CT embankments tend to be greater with an increase of the embankment height. In the FGT embankment, the soil arching effect is slightly weakened and the load transferred through the soil arching effect is reduced. The FGT embankment promotes a higher tensioned membrane effect and the load transferred through the tensioned membrane effect is increased significantly.(3) Based on the discussion about the mechanical characteristics of FGT embankment, a simplified check method of the requirement of geosynthetic tensile strength is proposed. Then, the load transfer mechanism of geosynthetic, pile and subsoil under the embankment load is analyzed. The embankment and improved area are treated as a whole with continuous displacement and stress. The geosynthetic is modeled as a thin plate and the deformation is calculated by the thin plate theory. The soil arching in the embankment and the interaction between pile and soil are also considered. A mechanical model of FGT embankment is proposed. Two conditions, the pile cap and pile beam conditions are considered in the mechanical model. The finite difference method is used to solve the mechanical model owing to the complexity of the soil strata. Then, the numerical procedure is programmed. Finally, a field test is conducted to verify the mechanical model and the calculated results are in good agreement with field measured data.(4) The numerical analysis is performed to investigate the performance of FGT embankment. In the FGT embankment, the geosynthetic and pile are treated as conode at the top of pile to model the fixing system. The model calibration is conducted to ensure a good representation of the numerical modeling for the embankment application. A parametric analysis on the influencing factors is conducted to investigate the performance of FGT embankment, which include the elastic modulus of soil, tensile stiffness of geosynthetic, pile length, pile spacing, pile elastic modulus and traffic load. Based on the numerical results, the cost evaluation between the FGT and CT embankments is also compared. The results show that the FGT embankment can reduce the settlement, enhance the stability and be a more economical and effective scheme for the embankment construction.(5) A two-dimensional numerical simulation by coupled mechanical and hydraulic modeling is conducted to investigate the time-dependent behaviors of FGT embankment including the settlement, differential settlement, lateral displacement, geosynthetic tension, excess pore water pressure, etc. A sensitivity analysis is performed to discuss the influencing factors such as tensile stiffness of geosynthetic, pile wall spacing, elastic modulus of soft clay, elastic modulus of pile wall and pile wall width. The results show that the excess pore water pressure at the end of construction in the CT embankment is much larger than that in the FGT embankment. In comparison with CT embankment, the FGT embankment can sufficiently reduce the post-construction settlement, differential settlement and lateral displacement, and enhance the stability of embankment during the post-construction period. During the construction period, the pile wall spacing and elastic modulus of pile wall have medium to high influences on the performance of FGT embankment. During the post-construction period, the elastic modulus of soft clay, pile wall spacing and elastic modulus of pile wall have high influences on the performance of FGT embankment. |
