Analytical Study On Backfill Height Of Intake Tower Built On The Bank In Seismic Area

Because of its wide adaptability to geological conditions,intake tower built on the bank is widely used in large and medium-sized hydropower stations in China.According to the previous research on its seismic performance,reasonable backfill height and backfill material can improve the mechanical performance of the tower structure.However,the current research on the backfill height of the back of the tower is not sufficient,and the relevant literature is few,and all of them are finite element analysis for specific projects,and the conclusions are not universal.In view of this,this paper uses analytical method to study the reasonable range of the backfill height of the tower back,the main contents are as follows.1)On the basis of the existing research results,based on the stress and deformation characteristics of the tower structure under the horizontal earthquake action,this paper simplified the tower back backfill support and the tower bottom foundation into L-shaped elastic foundation,and simplified the intake tower built on the bank on the vertical bank into Timoshenko beam on the foundation.According to the quasi-static method recommended by the current code for seismic design of hydraulic engineering,the expressions of displacement and internal force of tower under horizontal earthquake are derived,and the internal force solution program is compiled.2)Taking a 46 m high intake tower built on the bank project as an example,the influence of different backfill materials,concrete materials,height width ratio,section height width ratio and bottom restraint conditions on the lateral displacement,internal force and stability of the tower body under different backfill height ratio of the tower body are discussed by using the derived analytical formula and the solution program analyze the applicability of the calculation model to different height intake tower projects.3)In view of the influence of the vertical force of the tower intake can not be ignored sometimes,on the basis of reference to relevant research,considering the influence of the tower body weight,the vertical seismic inertia force,the axial friction of the tower back,etc.,the differential formula of Timoshenko beam motion on the L-shaped elastic foundation is deduced again,and the semi analytical method is used to solve the problem,and the internal force solution program is compiled,and then the literature is used to solve the problem Three typical engineering examples of intake tower are verified,and the influence of axial force on lateral displacement,internal force and stability of tower body is discussed.The research shows that the mechanical model and the analysis method are reasonable and feasible,and the distribution law of transverse displacement,bending moment and shear force along the tower height can be understood,so that the tower body is both economical and safe.Therefore,the optimal scope of the backfill height and the size of the tower body can be estimated.It is considered that the optimal backfill height ratio of the tower back should be between 0.4 and 0.7.It is suggested to choose the material the foundation resistance coefficient of which between 4500 ~ 15000MPa/m as the backfill of the back of the tower.It is recommended to select the concrete with small elastic modulus as far as possible under the condition of ensuring the strength.It is suggested that the optimal height width ratio is between 2 ~ 5.75,and it is suggested that the section height width ratio is between 0.9 ~ 1.5.The research in this paper can provide useful reference for the seismic design of the tower intake in the seismic area.