An Investigation Of The Load Carrying Capacity Features And Technique Of Settlement Computation For CFG Pile Composites Bases

The scale of domestic infrastructure is expanding year by year,and various technical problems are often encountered during construction,such as the bearing capacity and deformation of the foundation caused by poor foundation can not meet the requirements of national specifications.Among them,CFG pile composite foundation is widely used,which can effectively improve the bearing capacity of poor foundation and have strong resistance to deformation.However,through the analysis of the current actual engineering situation,it can be seen that the foundation settlement calculated according to the current specifications is often greater than the actual monitoring value,that is,the safety factor is large,and the calculation process is complex.In view of the above problems,based on a resettlement house project in Lucheng Town,Tongzhou District,this paper explores the change law of bearing capacity and deformation of CFG pile composite foundation and CFG single pile through field test and numerical simulation analysis,and optimizes the design scheme.On this basis,the compression modulus multipleof composite foundation in the code method is modified.At the same time,a correction method for settlement calculation of CFG pile composite foundation is proposed,and the correction method is verified by combining the actual settlement measurement data of Sunhe resettlement house project and Jinzhan resettlement house project in Chaoyang District,which provides a reference for the design and construction of similar projects.The main contents and achievements of this paper are as follows:(1)Based on the CFG pile test data and settlement monitoring data of a resettlement house project,the bearing capacity and deformation characteristics of CFG single pile and CFG pile composite foundation are obtained.FLAC 3D software is used to simulate and analyze CFG single pile and CFG pile composite foundation,and the accuracy of the model is verified by field data.At the same time,the foundation treatment design scheme of the project is optimized.And more in-depth study of the pile shaft axial force,pile side friction,bearing characteristics of the soil stress field of the composite foundation,displacement of the cushion layer,pile-soil displacement and other deformation characteristics.(2)Using the numerical simulation analysis of CFG pile composite foundation,the influence of these parameters on settlement is discussed by changing the three parameters of compression modulus,cohesion and internal friction angle of soft soil layer and pile tip soil layer in the composite foundation.Finally,it is concluded that the compression modulus is the most sensitive factor affecting the settlement,which provides a basis for the later correction of the compression modulus of the code method and the proposed correction method of settlement calculation.(3)Through the settlement monitoring data of actual engineering cases,it is found that the settlement value calculated by the standard method is conservative.According to the measured settlement data when the base bearing layer is cohesive soil and sandy soil respectively,the composite foundation compression modulus multipleV.When the base bearing layer is cohesive soil,the modulus correction coefficient of composite foundation is taken as 2.22(?) and the calculated value of settlement deformation is closer to the real value;When the base bearing layer is sandy soil,the modulus correction coefficient of composite foundation is taken as4.85Vand the calculated settlement deformation value is closer to the real value.In addition,in order to predict the settlement more accurately,a modified settlement calculation method is proposed,which is based on the additional stress generated by the earth pressure between pilesσ_s.Additional stress at the pile end caused by pile side friction and end resistance σ_d to calculate the settlement value.And the correction method can reflect the interaction between piles and soil,can also reflect the nature of the soil layer at the pile end,and also reflects the phenomenon of sudden increase in the additional stress at the pile end.(4)The modified settlement calculation method proposed in this paper is used to calculate the two projects in which the foundation bearing layer is located in cohesive soil and sandy soil respectively.Combined with the measured settlement data of CFG pile composite foundation of 30 buildings in the two projects,the standard method,the modified method and the measured values are compared and analyzed at the same time.The error rate of settlement value calculated by this correction method is mostly within 15%,which can effectively improve the accuracy of settlement calculation when the bearing layer of CFG composite foundation base is cohesive soil and sandy soil.