Study On The Mechanical Properties And Application Of A New Type Diaphragm Wall For Long-Span Arch Bridge

The diaphragm wall exhibits various advantages,including high stiffness,large bearing capacity,mature construction technology,and strong adaptability to complex geological conditions.Hence,it is an ideal form of foundation structure for long-span arch bridge.At present,the application of long-span arch bridge diaphragm wall to engineering projects is still not common,with a lack of mature calculation methods and engineering application experience.Based on the existing engineering applications and related studies,this paper puts forward the concept and structural system of a new type of diaphragm wall for the long-span arch bridge and carries out investigation into the structural system,simplified calculation methods,structural mechanical properties,and engineering applications of the new diaphragm wall.The main research contents and results are as follows:1.The concept and structure system of a new type diaphragm wall foundation for long-span arch bridge are proposed.The new type diaphragm wall foundation is a reasonable stress,low cost and convenient construction foundation structure,which the wall rock-socketed or not,the cap elevation,soil characteristics of bearing layer,and the connection mode between the cap and the wall are based on comprehensive consideration of the characteristics and stress requirements of the arch rib structure,geological conditions,construction conditions and time limit requirements,etc.According to the wall rock-socketed or not and the connection mode between the cap and the wall,four structural systems of new diaphragm wall of long-span arch bridge are proposed which are integral rock-socketed structural system,separated rock-socketed structural system,integral non-rocksocketed structural system,and separated non-rock-socketed structural system.The mechanical properties of different structural systems are significantly different,therefore it is of great significance for engineering application to choose the proper structural system to reduce the project scale,the construction difficulty,risk and cost,etc.2.The simplified calculation formulae of vertical and horizontal load of diaphragm wall and the displacement limit of arch foot of arch bridge are deduced:(1)The calculation formula of internal force of wall structure of diaphragm wall foundation subjected to vertical load is deduced by static balance based on the reasonable assumption of the relationship between wall side resistance,wall bottom resistance and soil core resistance and the corresponding stress distribution according to existing related research results,which is verified by comparison with the finite element numerical calculation results.Based on the elastic mechanics theory of semi-infinite foundation and the layer-wise summation method,the simplified equation for calculating the internal force and settlement of diaphragm wall foundation subjected to vertical load are derived,and the computation program is developed using MATLAB,which is verified by comparison with calculation results of the reference examples.(2)Based on the Timoshenko’s beam theory,theory of beam on elastic foundation,and Winkler foundation model,this study deduces the analytical solution for the diaphragm wall foundation subjected to horizontal load.The subsection undetermined coefficient method is applied to calculate the internal force and displacement of the foundation under complex conditions such as layered soil,varying stiffness,and m method,and the computation program is developed using MATLAB,which is verified by comparison with the finite element numerical calculation results and the testing data of the reference examples.(3)Based on the Principle of Force Method in structural mechanics,the simplified calculation formula of the displacement limit value of arch foot of arch bridge is derived.Firstly the additional stress expression(non-integral form)of the displacement of arch foot is derived based on the simple case of quadratic parabolic arch axis and uniform cross section stiffness of arch rib,then it is proved through finite element numerical calculation that the variation of arch axis and the variation of the cross section stiffness have little influence on the calculation of additional stress,which can be neglected,therefore the calculation formula based on the simple case can be used as a general formula.According to the deduced calculation formula,the displacement limit value of arch foot is related to the risespan ratio,span,elastic modulus,section height and the additional stress limit value,and it is quadratic parabola relation between the horizontal and vertical displacement limit values of arch foot and span,whereas it is linear relation for the rotational displacement.For a specific bridge The rise-span ratio,span,elastic modulus and section height are determined,the displacement limit value of arch foot can be calculated only by the additional stress limit value,which is determine d by material of the arch rib and the arch rib stress safety.3.The simplified calculation method proposed in this paper are used to analyze the relationship of the mechanical properties of the new diaphragm wall foundation with factors such as structural system,material properties,cap position,and structure size,so as to provide reference for engineering application.4.Pingnan No.3 bridge project is taken as an example in this paper to lay out the details related to the design,construction,and operation of the new diaphragm wall for the long-span arch bridge.Pingnan No.3 Bridge is a concrete-filled steel tube arch bridge with a span of 575 m,which is also the largest arch bridge in the world.A new type of diaphragm wall foundation of separated rock-socketed structural system is adopted on the north bank of the bridge which is the first application for long-span arch bridge.At present,the bridge is in good operating condition,and the relevant test and monitoring data show that the diaphragm wall foundation of the bridge has good mechanical properties.The successful application of the new diaphragm wall foundation of the bridge shows that the research results of this paper have good engineering practicability,and can provide references for related research and engineering application.