| The diaphragm wall foundation is widely used in bridge foundation engineering because of its high overall stiffness,high horizontal bearing capacity,strong seismic resistance and low cost.The cross-section forms of diaphragm wall foundation are various.The shaft diaphragm wall foundation with four-chamber cross-section is also called the Tianzi diaphragm wall foundation.The foundation of Tian-shaped diaphragm wall is large in size,and the full-scale field test workload is huge,so it is difficult to carry out.Nowadays,the finite element numerical simulation method has been widely used in large and complex engineering problems.ABAQUS is widely regarded as the most powerful finite element software.In this paper,the finite element software ABAQUS is used to carry out numerical simulation analysis,and then the theoretical calculation method is used to discuss the bearing characteristics of the Tianzi diaphragm wall foundation.In this paper,two-dimensional models of single-chamber,double-chamber and open caisson diaphragm wall foundations under homogeneous clay foundation are established.The settlement isoline diagram and displacement vector diagram of the three foundations are obtained by using finite element software,and the failure mechanism of the three foundations under vertical load alone is analyzed.It is concluded that the three foundations are shear failure under vertical load alone.Furthermore,a three-dimensional model of the field diaphragm wall foundation under homogeneous clay foundation is established.The failure modes of the foundation are similar to the conclusions of the two-dimensional simulation calculation,and both of them show the characteristics of shear failure as a whole.The load-bearing ratio curves of three kinds of foundations are obtained by using finite element software.The analysis shows that the external load of the foundations is mainly composed of four parts: external friction,internal friction,core reaction and end resistance.Outside friction and end resistance are the main factors.The influence of friction coefficient and buried depth between foundation and soil on ultimate bearing capacity of single chamber underground diaphragm wall foundation is analyzed.It can be concluded that the friction coefficient between foundation and soil has little effect on ultimate bearing capacity of foundation,and buried depth is the main factor affecting ultimate bearing capacity of foundation.In this paper,the foundation of double-chamber underground diaphragm wall under homogeneous clay foundation is established,and the failure mechanism and ultimate bearing capacity of double-chamber underground diaphragm wall foundation under horizontal load or moment load alone are analyzed.It can be concluded that the failure mechanism of double chamber underground diaphragm wall foundation under horizontal ormoment loads is similar.All of them revolve around a point below the ground and above the base,forming a spherical revolving failure surface inside the foundation.The soil in front of the foundation is squeezed to form a passive side failure wedge,and the active side failure wedge is formed behind the foundation.The load on the foundation increases linearly with the increase of displacement(rotation angle).When the displacement(rotation angle)increases to a certain value,the load on the foundation does not increase with the increase of displacement(rotation angle).Sweep loading method(Swipe loading method)and fixed displacement ratio loading method(Probe loading method)are used to analyze the envelope characteristics of foundation failure of double chamber underground diaphragm wall foundation.The envelopes of foundation failure on V-H,V-M and H-M loading surfaces can be obtained.The results show that on V-H loading surface,the vertical bearing capacity of double-chamber underground diaphragm wall foundation decreases with the increase of horizontal load,while the horizontal bearing capacity decreases with the increase of vertical load.On the V-M loading surface,the moment bearing capacity of double-chamber underground diaphragm wall foundation decreases with the increase of vertical load,and the vertical bearing capacity decreases with the increase of moment load.On the H-M loading surface,the effects of horizontal load and moment load interact.When the direction of horizontal load is opposite to that of moment load,the failure load of foundation increases with the increase of horizontal load.When the moment load reaches the moment limit load,the damage envelope decreases sharply.The ultimate horizontal ultimate load is achieved.When the direction of action of horizontal load is the same as that of moment load,the load under failure decreases with the increase of horizontal load in the same direction.Among them,the burial depth is still the main factor affecting the envelope shape of foundation failure.With the increase of burial depth,the envelope of foundation failure gradually enlarges.Relying on the project of "Bridge Investigation and Design of the Yangtze River Diversion Project(Anhui Section)"(Hetong-Huangdao Expressway Passing over Caizihu Section Channel).Based on the actual stress state of the actual project,a three-dimensional finite element model is established by using the finite element software ABAQUS.The bearing characteristics of the foundation of Tianzi diaphragm wall under vertical,horizontal and combined loads are discussed by applying actual loads.Through "Code for Design of Highway Bridge and Culvert Foundation and Foundation"(JTG D63-2007)and eight spring rigid foundation analysis methods,the displacement characteristics of Tianzi diaphragm wall foundation are analyzed theoretically and compared with the results of finite element calculation.It can be concluded that the foundation of Tianzi diaphragm wall has large overall stiffness and high bearing capacity.Under the action of external forces,thefoundation presents the characteristics of overall failure."Code for Design of Highway Bridge and Culvert Foundation and Foundation"(JTG D63-2007)and eight spring rigid foundation analysis methods can well calculate and fit the displacement characteristics of Tianzi diaphragm wall foundation. |
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