Research On Displacement And Bearing Capacity Of Rectangular Closed Diaphragm Walls Bridge Foundation

The rectangular closed diaphragm wall is a new type of bridge foundation,and possesses the advantages,such as strong rigidity,high bearing capacity and good aseismic performance.However,the complexities of load transfer mechanism,bearing characteristics and the immaturity of calculation method have hindered the development and application of this foundation pattern.Currently,the methods for the horizontal displacement are called as eight springs and four springs respectively for rigid and elastic rectangular closed diaphragm walls,and the calculation of vertical settlement is mainly based on the load transfer approach.These calculation methods are based on Winkler foundation model,in which the soil mass surrounding the wall is regarded as a series of discrete springs.The Winkler model is simple,convenient and strong empirical,however,the model can't reveal continuity of the soil,the size effect of foundation and the influence of transversely isotropic properties of soil.Furthermore,few studies have been put forward for the theoretical calculation method of dynamic response and the bearing capacity of foundation under combined loadings.Therefore,this paper presents the analysis models to calculate the response of vertically and laterally loaded rectangular closed diaphragm wall foundation with the aid of modified Vlasov model,reveals the mechanisms of the vertical and horizontal soil resistance,and proposes failure envelopes of the foundation,which can be utilized to estimate stability under combined loadings.The main research works and conclusions are listed as follows:(1)A semi-analytical method for analysis of laterally load rectangular closed diaphragm wall is presented based on the modified Vlasov foundation model.The diaphragm wall-soil system is modeled as a continuum and a horizontal displacement scheme is proposed on the basis of displacement compatibility of diaphragm wall and soil within the framework of wall-soil static interaction for laterally loaded rectangular closed walls.The potential energy functionals of diaphragm wall and soil deposits are established in the isotropic and transversely isotropic multilayered soils respectively based on the Timoshenko beam model and the assumed displacement scheme.The governing equations and boundary conditions are obtained by using the principle of minimum potential energy.The horizontal displacement and bending rotation functions for laterally loaded rectangular closed walls are decoupled by a mathematical transformation function.The reaction of the soil is established and the mechanism of horizontal soil resistance is explained.The horizontal displacement function and the decay functions of the soil are decoupled and solved by an iterative algorithm numerically.The proposed method is verified by comparing special cases of our model with the existing solutions.Numerical examples are performed to investigate the influence of soil core,rectangular section size and degree of anisotropy on the static response of laterally loaded rectangular closed diaphragm walls foundation.(2)A semi-analytical method for the loaded-settlement analysis of rectangular closed diaphragm wall is presented based on the modified Vlasov foundation model.With consideration of displacement compatibility,a settlement scheme for vertically loaded rectangular closed diaphragm walls is presented as the wall-soil is treated as a continuum.The potential energy functionals of diaphragm wall and soil deposits are established in the isotropic and transversely isotropic multilayered soil respectively with aid of the vertical displacement scheme and fictitious soil pile model.The governing equations and boundary conditions of closed diaphragm walls,soil column and soil deposits are obtained by using the principle of minimum potential energy.The skin resistance of closed diaphragm walls is derived and the physical mechanism is revealed.The vertical displacement function and the decay functions of soil deposits are decoupled and solved by an iterative algorithm numerically.The accuracy of the present method and calculation program is verified against the solutions available in the literature.A parametric study is conducted to study the influence of soil core,cross section shapes and transverse isotropy on the axial diaphragm walls deflection,axial force and skin resistance.(3)A semi-analytical approach for dynamic response of laterally load rectangular closed diaphragm wall is developed by the modified Vlasov foundation model.On the basis of lateral dynamic diaphragm wall-soil interaction,the horizontal displacement scheme with separable variable technique is proposed for laterally loaded rectangular closed walls.Energy functionals of wall-soil system are obtained according to the Timoshenko beam model and the assumed displacement scheme in the isotropic and transversely isotropic viscoelastic multilayered soils.The horizontal displacement and bending rotation functions are decoupled by a mathematical transformation function.The dynamic resistance is established and the mechanism of horizontal resistance is unveiled.The horizontal displacement function and the decay functions of soil deposits are decoupled and solved by an iterative algorithm numerically.The results of our model agree well with the special cases in the existing solutions.Numerical analysis is performed to investigate the effects of the thickness of diaphragm wall,cross section shapes and transverse isotropy on the horizontally complex stiffness at the top of diaphragm walls.(4)A semi-analytical approach for dynamic response of vertically load rectangular closed diaphragm wall is developed by the modified Vlasov foundation model.Bsed on vertically dynamic diaphragm wall-soil interaction,the vertical displacement scheme with separable variable technique is proposed for vertically loaded rectangular closed walls.Energy functionals of wall-soil system are derived according to the fictitious soil pile model and assumed displacement scheme in the isotropic and transversely isotropic viscoelastic multilayered soils.The dynamic shaft resistance is established and the physical mechanism is unveiled.The vertical displacement function and the decay functions of soil deposits are decoupled and solved by an iterative algorithm numerically.Comparisons with the available solution confirm the accuracy of the proposed solution.A parametric study is conducted to study the influence of soil core,cross section shapes and transverse isotropy on the vertically complex stiffness.(5)The H-M envelope of bearing capacity for rectangular closed diaphragm walls foundation with different height width ratio,friction coefficient between diaphragm wall and soil and vertical load ratio are obtained through the finite element models by the fixed displacement ratio loading.The accuracy of the wall-soil contact model in the finite element models is verified by comparing the bearing capacity coefficient of shallow foundation calculated in this paper with available solution in the literature.The envelope of the shallow foundation is obtained by the loading method with fixed displacement ratio(Probe test),and the correctness of the loading method is verified by comparing with the classical envelope in literature.The influences of aspect ratio,friction coefficient and vertical load ratio on H-M envelope are discussed.