Study Of P-y Curve Calculation Method For Pile Retaining Structure Of Foundation Pit

With the large-scale infrastructure construction and urban underground space development deepening,there have been a lot of deep foundation pit.Using appropriate methods to calculate the internal forces and displacements of the excavation envelope more accurately is one of the important contents of the design of the foundation pit.Among them,the elastic fulcrum method based on the theory of beam on elastic foundation is widely used in the calculation of the deep foundation ditch enclosure structure.The elastic fulcrum method based on the theory of beam on elastic foundation assumes that the soil below the excavation face of the foundation pit is always in the elastic state during the excavation of the foundation pit.However,when the deformation of the retaining structure is large,the soil inside the foundation pit may yield and enter into the plastic state.Under this condition,the deformation of soil inside foundation should be considered into the plastic state when calculating the deformation of the deep foundation ditch enclosure structure.In view of the calculation method of the foundation pit retaining structure not enough,this paper proposes the improved calculation method of the deep foundation ditch enclosure structure.The main contents of this paper are as follows:(1)P-y curve method considerses the nonlinear displacement of soil,and it is in accordance with the actual state of the inner soil which is compacted by the deep foundation ditch enclosure structure.Therefore,this paper uses p-y curve method to calculate the displacement value and internal force of the deep foundation ditch enclosure structure in the actual project,compared with the calculation value of the incremental analysis method for beam on elastic foundation and the measured value to verify its rationality and superiority.The results show that:Compared with the measured displacement curve,the lateral displacement curve of the deep foundation ditch enclosure structure calculated by the p-y curve method is not only in line with the actual deformation law of the deep foundation ditch enclosure structure,but also closer to the measured value than the result calculated by the incremental analysis method for beam on elastic foundation.Both the theory and the practice show that it is reasonable to use the p-y curve method to calculate the displacement of the deep foundation ditch enclosure structure.(2)Although the calculation method of the foundation ditch enclosure structure based on p-y curve has considered the actual situation which the soil of inside of the foundation pit may enter into the plastic state,it has not considered the latera displacement of the retaining wall when the internal bracing is erected,which starts working after the retaining wall has occurred the initial displacement.In view of the above shortcomings,this paper presents a calculation model of the foundation ditch enclosure structure based on p-y curve,considering the initial displacement of the retaining wall where the internal bracings erect at the time of bracing;The finite difference equations and methods for lateral displacement calculation of enclosure wall are established,and the rationality of the proposed method is verified by engineering examples.The results show that:Compared with the traditional p-y curve method and the incremental analysis method for beam on elastic foundation,the results from the displacement form of the calculation result,the value of the maximum displacement and the position where it appears calculated by the p-y curve method proposed this paper is closer to engineering measured value.The wall distribution of force calculated by the p-y curve method proposed this paper can avoid the risk of walls bending moment is too large,and it's in line with the actual project situation.Theoretical analysis and engineering examples are all shown that:Compared with the traditional p-y curve method and the incremental analysis method,the calculation results from the p-y curve method proposed in this paper is more in line with the actual project results.