| Abstract:The post-construction settlement of high-speed railway bridge pile foundation directly affects the comfort and safe operation of high-speed railway line, and it even decides the success or failure of high-speed railway construction. But because of the shortage of pile foundation settlement computation theory, in addition to calculation parameters hard to obtain, there is large difference between the calculated result and the measured result of pile foundation settlement. Especially in the post-construction settlement of pile foundation in the soft soil region, there was not a set of practial computation theory. Current codes just provide control standards of the post-construction settlement and the differential settlement of pile foundation. The post-construction settlement of bridge pile foundation is a long-term deformation compatibility system of pile, cap and soil, and it has been one of the most difficult problem in geotechnical engineering, and its theoretical research fell far behind engineering application. This dissertation stems from the key project of the former China Ministry of Railway and the scientific research project of Shanghai Railway Bureau, mainly by combining methods of field monitoring, laboratory tests, theoretical analysis and numerical simulation to study the long-term (post-construction) settlement characteristic and the bearing characteristic of high-speed railway bridge pile foundation in deep soft soil region.The issues in this dissertation are generalized as follows:(1) Basic physical and mechanical properties of soft clay in high-speed railway were analysed by laboratory tests, and the creep property of soft clay was researched by long-term creep test. The results show that the soft clay has obvious creep effect, and the Koppejan model can describe the creep property of this soft clay very well.(2) Based on the layer-wise summation method, a computational method for post-construction settlement of bridge pile foundation considering creep effect was established by using the stress ratio method to calculate the compressed layer thickness and the Koppejan model to describe the relationship of stress-strain-time of pile bottom soil. A calculation procedure named CPPS-I was compiled by this method. Using CPPS-I to calculate the post-construction settlement of a representative bridge pile foundation, the results show that this method can well calculate the post-construction settlement of bridge pile foundation in soft soil region, and the assumption of this method is reasonable, what’s more, the physical significance of parameters is clear, which can be obtained by simple soil test. The effects of primary consolidation coefficient and secondary consolidation coefficient of foundation soil, bearing stratum, preloading time after girder erection on the post-construction settlement of high-speed railway bridge pile foundation in soft soil region were studied by this method.(3) On the basis of the shear displacement method, and considering the effect of pile groups constraint, a computational method for long-term settlement of bridge pile foundation was established by using the Burgers model to describe the creep property of soil around pile and below pile tip. A calculation procedure named CPPS-Ⅱ was compiled by this metbod, which was used to calculate the long-term and post-construction settlement of a representative bridge pile foundation. The results show that this method can well calculate the long-term and post-construction settlement of bridge pile foundation in soft soil region. The effects of primary consolidation coefficient and secondary consolidation coefficient of foundation soil, bearing stratum, preloading time after girder erection on the post-construction settlement of high-speed railway bridge pile foundation in soft soil region were studied by this method. The effects of bearing stratum, pile distance, pile number and preloading time after girder erection on the long-term settlement of high-speed railway bridge pile foundation in soft soil region were studied by this method.(4) The Koppejan creep model was improved by using an incremental form to describe the relationship of stress-strain-time of soft soil. This model was made secondary development for a soft soil creep constitutive model by the UMAT subroutine of ABAQUS, which was verified by long-time creep test, triaxial creep test and long-term settlement of pile example. The verification results show that the improved Koppejan model can describe the creep property of soft soil, and secondary development of this model can be used for numerical simulation analysis of soft soil long-term deformation.(5) An elastic-viscous plastic constitutive model for interface was deduced by the nolinear elastic constitutive relation of the Goodman contact element. This model was made secondary development by the FRIC subroutine of ABAQUS, which was verified by interface shear test.The verification results show that the elastic-viscous plastic constitutive model for interface can describe the rheology constitutive relationship of interface, and secondary development of this model can be used for numerical simulation analysis of pile foundation in soft soil.(6) Long-term field monitoring of the compression of pile tip soil, the pile strain, the pile compression, the compression of soil between piles was conducted at four typical bridge piers of two construction sites in the Hangyong railway passenger dedicated line. Changing rules over time of the compression of pile tip soil, the pile compression, the pile axial force, the pile skin friction and the compression of soil between piles were studied to provide reference for the design and construction of high-speed railway bridge pile foundation in soft soil region.(7) Three-dimensional finite element models of No.327pier of the Keqiao grand bridge and No.667pier of the Ninbo grand bridge in the Hangyong railway passenger dedicated line were established by ABAQUS, of which soft soil uses the secondary development model of the improved Koppejan creep constitutive model, and pile-soil interface uses the secondary development model of elastic-viscous plastic constitutive model for interface. Changing rules over time of the post-construction settlement, the pile axial force and the pile skin friction was studied to reveal the long-term deformation and the distribution of internal force of high-speed railway bridge pile foundation in soft soil region. The effects of upper load and pile length on the long-term settlement and internal force of pile foundation was researched by using the finite element model of No.667pier.(8) According to the research results in this dissertation, practical measures and suggestions for controlling the post-construction settlement of high-speed railway bridge pile foundation in soft soil region were proposed to give reference for the design and construction of high-speed railway bridge pile foundation in soft soil region. |
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