Research On Working Mechanism And Numerical Simulation Of Double-row Piles And Soil Nail Composite Supporting Structure

The double-row piles and soil nail composite supporting structure has the advantages of large side stiffness resistance,shortened construction period,and ease of construction,and is particularly applicable to deep foundation pit projects with strict requirements for deformation and strict requirements for supporting space of foundation pits.The double-row piles and soil nail composite supporting structure is a new composite support system based on double-row piles supporting structure and vertical soil nails installed between the piles.At present,the study on the stress deformation of double-row piles and soil nail composite support is not very systematic.This paper uses numerical simulation methods to analyze the deformation of the double-row piles and soil nail composite supporting structure during construction.On this basis,according to the geometric characteristics of the double-row piles and soil nail composite system,consider the gravity effect of the soil between piles,study its cooperative working mechanism,and establish a simplified calculation method of its force deformation.The main research contents and results are as follows:(1)The finite element method was used to establish the numerical model of the double-row piles and soil nail composite supporting,and the deformation and deformation characteristics of the foundation pit during excavation and support construction were simulated,comparison and analysis of forced deformation of double-row piles supporting structure.The results show that: double-row piles composite soil nailing support structure adopting larger row spacing,the soil nail can not only pull anchor effect on the front row of piles,but also improve the strength of the soil between the piles.The overall stiffness is larger,and the soil between the piles exerts its gravitational effect,so that the overall lateral displacement of the supporting structure and the maximum bending moment of the front and rear row of piles decrease.(2)Based on the numerical simulation method,the design parameters such as the front and rear rows of piles distance,depth of embedment,pile diameter and soil nail length were changed,and the influence of various parameters on the force deformation of the composite support structure was analyzed.The results show that: increasing the front and rear rows of piles distance,pile diameter and soil nail length can significantly reduce the lateral displacement of the foundation pit,and there are reasonable combinations between various design parameters based on different optimization design goals.(3)The finite element strength reduction method was used to simulate and analyze the overall stability of the foundation pit,and based on the above-mentioned parameter changes,the effect on the safety coefficient of the foundation pit stability was analyzed.The results show that: When the foundation pit is destabilized to failure,the sliding surface is a wedge-shaped sliding surface that has evolved into a pile bottom around the pile.Increasing the front and rear rows of piles distance,depth of embedment and soil nail length can significantly improve the overall stability of the foundation pit.(4)Based on numerical simulation results,using theoretical research methods,simplified analysis of front and rear earth pressures of front and rear row piles.Considering the working conditions,the theoretical calculation formula of the force and deformation of the composite support system is deduced by analytical method.Through comparison with numerical simulation results,verify the rationality of the theoretical calculation formula of this paper.