Research On The Calculation Method Of Deformation And Stability Of Row Piles And Soil Nailing System

Row piles and composite soil nailing structure,which combine row piles and soil nails,is a new type of bracing structure of foundation pits.Row piles as a vertical structure,it is able to overcome the shortcomings of large displacement of traditional soil nailing supporting foundation pits,because of its great stiffness. And through the grouting soil nails improve properties of undisturbed soil, and get re-distribution of soil stress, increase the stability of the soil between row piles.Both interact to limit the deformation of foundation pits together and maintain the stability of foundation pits.If the surrounding environment of the foundation pits is complex, it need more stringent requirements for the deformation,prestressed soil nails will help to further reduce the displacement of pit sidewalls.Currently, Row piles and composite soil nailing structure has been applied in the actual projects,however,the related researches of the retaining structure are little, cognitive theories are far behind the engineering practice.Based on this, in this paper, using the finite element numerical simulation and combined with theoretical analysis to study the influence on force,deformation and the stability of row piles and composite soil nailing structure by prestressing. Then this paper deduces the simplified calculation method of horizontal displacement of the retaining structure and the retaining structure under prestressed soil nail conditions based on the law of force and deformation of this structure.The overall stability of this structure has been analysed by using strength reduction method,and establish the calculation formula of the overall stability of row piles and composite soil nailing structure, The main research results and conclusions are as follows:(1)Three-dimensional finite element model is established by ABAQUS finite element software,to simulate the effects of prestressed position and size of row piles and composite soil nailing structure,concluding force,deformation and the stability.Turn out that, the prestress in the upper part of the foundation pit slope is better for the decrease of the horizontal displacement of the soil between piles and row piles;the influence of ground surface settlement and bottom heave by prestressed position and size is very small,it can be neglected basically.(2)This paper establishes a calculation model of horizontal displacement of row piles based on elastic foundation beam method and combines with the theory of structural mechanics. The calculation model of deformation of soil nails is established by the axial force of soil nails of finite element simulation.To introduct incremental method,it deduces a simplified calculation method of horizontal displacement of row piles and composite soil nailing structure based on the deformation compatibility between row piles and soil nails by considering construction process. On the basis of this,it deduces a simplified calculation method of horizontal displacement of the retaining structure under prestressed soil nail conditions.This method is verified by finite element numerical examples which show this the method is reasonable.(3)The failure mode of row piles and composite soil nailing foundation pits is analysed by using the strength reduction finite element method, turn out that,the overall stability of foundation pits enhances with the increase of embedded depth of row piles and soil nailing length.But there is a threshold value; When the length of soil nails is certain, the sliding surface of foundation pits at failure transforms from arc under pile to pile bottom arc,and then transforms the arc cutting pile with the increase of the embedded depth of row piles;When embedded depth of row piles is certain, the sliding surface of foundation pits at failure transforms from the arc cutting pile to arc under pile with the increase of the length of soil nails.(4)Based on the analysis the role of row piles and soil nails in the overall stability,it estabilishes a calculationformula of overall stability of row piles and composite soil nailing foundation pits, through the finite element calculation example shows that the method of stability analysis is reasonable and feasible.