| In recent years,with the continuous development of urban agglomeration construction in China,the demand for sea-crossing and river-crossing channels adjacent to cities has increased significantly,and kilometer-sized long-span bridges have attracted more and more attention due to their good spatial ability.Large span,high bearing capacity and complex geological environment put forward higher requirements for structural foundation.As a new type of deep foundation,multi chamber diaphragm wall has excellent horizontal bearing capacity and deformation resistance,and has broad application prospects and engineering requirements..Based on the key technology research project of composite diaphragm wall anchorage foundation of Zhangjinggao Yangtze River Bridge,this paper studies the horizontal bearing characteristics of multi chamber diaphragm wall by means of laboratory test,numerical simulation and theoretical calculation.It mainly includes:(1)Through the unconfined compression test,wall-soil interface shear test and permeability test of cement soil,the physical and mechanical properties of reinforced soil with high cement ratio are studied.The influencing factors of cement soil strength and the failure mode of cement soil under high mixing ratio were explored,and the stress-strain curve of cement soil was obtained.Based on Zhangjiagang silty clay,the prediction formula of unconfined compressive strength of cement soil at any age was proposed.The shear characteristics of wall-soil contact interface were studied by large direct shear equipment.The results show that the friction coefficient of concrete-cement soil increases with the increase of cement curing age,and the friction coefficient of concrete-clay decreases rapidly with the increase of clay moisture content.Based on Mohr-Coulomb criterion,the minimum friction formula of reinforced soil biased towards safety and application is proposed.The permeability test of reinforced soil was carried out,and the results showed that the permeability coefficient of reinforced soil decreased with the increase of age.(2)Based on the three-dimensional finite element numerical simulation,the horizontal bearing characteristics of multi chamber wall foundation are studied.The results show that the foundation displacement is the result of the coupling of translation and rigid body rotation,then the wall displacement and the distribution law of soil resistance is further given.With the increase of horizontal load,the plastic zone develops outside the front wall and gradually penetrates up and down,resulting in local shear failure.By establishing models of different foundation types,the influence of base embedded end is studied,and the load distribution characteristics are analyzed.Finally,the foundation reinforcement is analyzed and evaluated.(3)Based on the Zhangjinggao Yangtze River Bridge project,the numerical model of multi chamber wall in layered soil is established and the wall foundation under combined load is studied.The distribution law of lateral soil resistance is given.Under the design load,multi chamber wall mainly bears horizontal load by front soil resistance and side friction,and vertical load by base and wall bottom.Due to the existence of the embedded end at the bottom,the foundation reinforcement is not as good as the traditional box foundation in improving the friction effect of the foundation.(4)Based on the theoretical calculation,the six spring analysis method and the code recommended method are used to calculate the displacement,rotation angle and soil reaction of multi chamber wall foundation under the design load in the operation stage.The results show that the six spring analysis method is in good agreement with the finite element results,and the displacement of wall top calculated by m method is seriously small because the foundation size effect is not considered.Based on this,a reduction method of proportion coefficient of foundation reaction coefficient considering the size effect is proposed in this paper. |
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