Research On Horizontal Bearing Characteristics Of Split Shaft Diaphragm Wall Anchorage Foundation

With the rapid development of bridge construction in China,the research on the form and stress of large bridge anchorage foundation is becoming more and more important.Split shaft diaphragm wall foundation is a new type of anchorage foundation of suspension bridge.It has simple foundation structure,convenient construction and great popularization potential.However,there is little research on the horizontal bearing characteristics of the foundation at present.There are a large number of soil cores in the foundation of split shaft diaphragm wall,and the stress deformation and horizontal bearing mechanism of the foundation are complex.Therefore,based on the anchorage foundation project of Sichuan Bank of Sichuan kahaluo Jinsha River Bridge,the horizontal bearing capacity and load transfer mechanism of split shaft diaphragm wall foundation are systematically studied and analyzed by means of field test,numerical simulation and theoretical calculation.The main research contents are as follows:(1)The in-situ soil mechanical property test of Sichuan bank anchorage foundation of kahalo Jinsha River Bridge was carried out to study the soil properties.The soil mass of Sichuan bank is mainly gravel soil,with high strength and good bearing performance.According to relevant specifications,the horizontal bearing roof test scheme of in-situ shaft diaphragm wall foundation is prepared,and the test method,equipment layout,loading program and data processing method of horizontal roof test are put forward.(2)The ABAQUS three-dimensional finite element model of single chamber shaft diaphragm wall foundation in gravel soil foundation is established,to study the horizontal stress and displacement law through numerical analysis.The foundation of single chamber shaft diaphragm wall shows an overall inclined failure mode.With the increase of external load,the rotation center of the foundation moves from the back wall to the front wall,and the depth remains basically unchanged.Based on the analysis of the failure form of soil,the top soil in front of the foundation first gives play to the bearing capacity.With the increase of external force,the horizontal load is gradually transmitted to the deep soil.Therefore,the plastic zone of soil first appears on the top outside the front wall and expands downward with the increase of depth until the wall tilts or the soil yield failure.Further,the earth pressure distribution form and load sharing ratio of the wall are analyzed.The horizontal load of the single chamber wall is mainly borne by the front and rear wall soil resistance and side wall friction,of which the front and rear wall soil resistance accounts for about 70%.The influence of vertical load on the horizontal bearing characteristics of shaft diaphragm wall is explored.The results show that the vertical load improves the horizontal bearing capacity of the wall to a certain extent.(3)The ABAQUS three-dimensional finite element model of split shaft diaphragm wall anchorage foundation under gravel soil foundation is established,and the horizontal bearing characteristics of split shaft diaphragm wall foundation are studied based on the research results of single chamber wall.The split shaft diaphragm wall foundation has 12 chambers in total.The foundation also shows the overall inclined failure mode,and the horizontal displacement of the wall is distributed in the form of fluctuation along the transverse direction.The earth pressure distribution form and load sharing ratio of the split shaft diaphragm wall foundation are analyzed.Compared with the single chamber wall,the soil resistance of the front and rear walls of the split wall accounts for 62%,while the horizontal friction resistance of the wall bottom and base increases.The models of single chamber wall,six chamber wall and split wall are established and loaded horizontally.Through comparison,it is found that there is group wall effect in multi chamber diaphragm wall.The stress overlap of multiple chambers and the weakening of soil core in the tube reduce the average bearing capacity of the chamber.The layout of split shaft diaphragm wall is conducive to reduce the influence of group wall effect.(4)The calculation theory and method of rigid foundation and elastic foundation spring method of diaphragm wall are put forword.The horizontal bearing capacity of split shaft diaphragm wall is calculated and analyzed by using rigid foundation spring method and domestic current rigid foundation m method.The results show that the calculation result of m method is small when calculating large-scale diaphragm wall,while the calculation of rigid foundation spring method can consider the action of soil core in the wall,and the result is more appropriate.