Study On The Mechanism Of The Foundation Reinforcement With The Bag Pile

In the field of geotechnical engineering,foundation reinforcement is often needed.As a new type of composite foundation reinforcement technology,the bag grouting pile has the advantages of convenient construction,environmental protection and so on.It avoids the loss of water resource and environmental pollution.As a new composite foundation reinforcement technology,due to the lack of theoretical support,this technology has not formed a unified industry standard,which affects the further application of this technology.In this paper,two-dimensional and three-dimensional expansion models of bag pile are established respectively considering the structural disturbance of soil.The theoretical solutions of stress field,strain field and water pressure field are obtained.FLAC3 D software is used to solve the numerical simulation.The theoretical solutions,numerical solutions and measured values are compared through case analysis,which proves that the theoretical model has a high applicability in the mechanism analysis of the bag pile.The main contents are as follows:(1)Considering the influence of structural disturbance of soil and initial stress,the surrounding soil is divided into elastic region and plastic region during expansion.A logarithmic in-situ strength disturbance function is proposed,and the soil sensitivity parameter is introduced to describe the disturbance effect.Based on the Mohr-Coulomb strength criterion,the two-dimensional theoretical model is proposed.The analytical solutions of stress field,strain field and displacement field are derived during expansion.The theoretical solutions of excess pore water pressure are derived by Henkel's water pressure formula.(2)The bag piles are often used to strengthen the deep foundation,so the cylindrical cavity expansion theory based on the plane assumption can not meet the actual engineering needs.On the basis of the twodimensional theoretical model,the three-dimensional theoretical model is established by considering the changes of the pile side pressure and friction with the depth.Through rigorous theoretical derivation,the quantitative indexes that can reflect the reinforcement effect of bag pile,such as the radius of plastic region,the ultimate expansion pressure are obtained,which can provide scientific basis for engineering quality detection and evaluation.(3)FLAC3D is used to establish the numerical model of the bag pile.Through the software simulation,the stress field,displacement field and water pressure during the expansion are studied.The numerical solutions are compared with the theoretical solutions to verify the applicability of the proposed model.(4)The construction process of the bag pile is studied,and the procedures,construction control points and quality inspection indicators of the bag grouting pile were summarized.(5)The two-dimensional and three-dimensional theoretical solutions are compared with the domestic and foreign engineering case data.The comparion proves that the theoretical model has high applicability in the mechanism analysis of the of bag grouting pile.