| As a new structure adapted for marine soft soil foundation,the frame-fixed soldier pile structures(FSPSs)have a set of special bearing mechanism and failure mode different from existing retaining structures with double-row piles and quay walls of sheet pile.Further theoretical analysis and experimental demonstration are essentials to reveal the distribution of soil pressure around the soldier pile and the load transfer mechanism of the pile-soil-pile system.PHC piles standing closely in the FSPS makes its pile spacing far less than that in the existing piled wharf structure and the retaining structure with double-row piles.Under the backfilling load,the deformed subsoil will laterally squeeze PHC piles and flow around the soldier pile.The interaction between soil and double-row piles depends on a variety of factors such as soil shear strength,soil compressibility,pile-soil relative stiffness,pile spacing,ratio of pile diameter to pile spacing and heaped loads,which motivates further study on establishing a computational model with sufficient precision to solve the pile displacement and internal forces.According to above problems,a series of work is carried out on FSPSs and their horizontal bearing capacity.The main contents and conclusions are as follows:(1)Based on the limit equilibrium theory,stress analysis and simplification of the FSPS are conducted to establish the stability model and its corresponding calculation method,in considering effects of pile spacing and the cutting pile force in the heterogeneous soil.A plane finite bar element model based on the elastic subgrade reaction method is established to solve the structural internal forces and displacement,with consideration of the influence of row spacing on the interaction between soil and piles by the way of load migrating.The above calculation method and plane finite bar element model are proved reasonable and feasible by field observations obtained form the test engineering of FSPS.Moreover,the factor analysis is conducted on the stability of FSPS and internal forces of pile foundation.(2)Combined with the engineering instance,an overall three-dimensional finite element model was established,which is validated by the engineering test observations.Then a series of three-dimensional finite element model for single row pile construction in homogeneous soil foundation is established,as pile spacing reducing from 8 D to 0.1 D,in order to compare differences in aspects of the deformation and the bending moment of pile body,the elevation of soil surface and the location of plastically deforming soil area.(3)A series of three-dimensional finite element model for double-row pile construction in homogeneous soil foundation is established.The similarities and differences between the front/rear pile of double-row pile construction and the single row pile construction are analyzed in aspects of the bending moment of pile body,the deformation of the soil around the pile,the location of plastically deforming area and the pile P-Y curve.While the front pile of double-row pile construction can be designed as the single row pile construction,the rear pile of that is consistent with the single row pile construction on the initial stiffness of the P-Y curve,and the limiting soil resistance of the rear pile is about 0.3～0.6 times that of the single row pile construction accroding to the displacement control standard.(4)In terms of FSPS,the horizontal load is mainly borne by the front pile,which is able to consider as the single row pile construction.Herein the investigation focuses on the P-Y curve of single row pile construction under horizontal load.The changing rules of P-Y curve with pile spacing,burial depth and soil index are analyzed by the finite element numerical calculation method.The limiting soil resistance and the initial stiffness of the pile P-Y curve are fitted nonlinearly,and the expression of P-Y curve for pile construction with small pile spacing is derived.(5)A calculation program of plane frame finite element model is written by using FORTRAN language according to the above P-Y curve expression.Based on elastic-plastic properties of soil foundation,the factor analysis is conducted on influencing factors of FSPS such as batter pile,pile spacing,pile length and elevation difference of soil surface between each side of FSPS.Results show that the inclined pile is effective for reducing the lateral displacement at pile top and improving the internal force distribution of the pile body.However,the deformation and the internal force of pile body change unobviously with further enlargement in pile length after the pile foot reaching a fixed state,or the variation of pile spacing from 0.1 D to 1 D. |
