Study On Inclination Characteristics And Rectification And Reinforcement Technology Of Large Chassis Building On Composite Foundation Of Filling Lime-soil Pile

With the rapid development of urban construction in China,the form of filling composite foundation combined with large chassis foundation is increasingly widespread.In practice,the uneven deformation of filling composite foundation results in the fracture of the large chassis foundation and the inclination of the building,which seriously affects the safe use of the building.Therefore,it is necessary to conduct in-depth study on the causes,mechanism and characteristics of the inclination of large chassis buildings,as well as the technology of rectification and reinforcement,which is of great significance for preventing similar accidents,taking timely remedial measures and ensuring the safety of public life and property.Based on an inclination rectification and reinforcement project of a large chassis building with a filling lime-soil pile composite foundation in Xi'an,this paper analyses the causes of the inclination of the large chassis building and the stress and deformation characteristics of the filling composite foundation and the large chassis foundation during the inclination process by means of indoor test and field monitoring,and by means of theoretical analysis and numerical simulation,and puts forward a method based on confining pressure(foundation depth).The settlement calculation method of the composite foundation of filling lime-soil pile is presented.The scheme of rectifying and reinforcing large chassis building by sleeve valve tube grouting technology is given.It has been applied to practical engineering and achieved good results.The main research work and achievements are as follows:(1)Compressive shear tests of lime soils with different compaction degrees,compaction coefficients,ratios and ages show that the compressive modulus,cohesion and internal friction angle of fills and lime soils are positively correlated with ash content,compaction degree and age,and different combinations of compressive shear indexes are brought into the numerical model calculation.By comparing the calculation results of each combination with field monitoring data,the results are obtained.To the actual combination of composite foundation.The results show that the compactness of the filling,the ratio of lime-soil piles and the compaction coefficient of the foundation do not meet the design requirements.The strength of the foundation soil is insufficient and the constraints on both sides of the building foundation are different,which results in a large uneven settlement of the building under the action of self-weight.This is the basic reason for the building inclination.At the same time,it is found that even if the design requirements are met,the building still has a large settlement deformation.The design of foundation treatment is unreasonable.(2)The numerical analysis method is used to study the mechanical and deformation characteristics of the composite foundation of filling lime-soil piles,and the mechanical and deformation characteristics of the large chassis foundation in the inclination process are analyzed.It is found that the composite foundation in the filling area has a large deformation under the force,and the settlement deformation at the edge of the foundation is larger and the shear deformation caused by the shear force is the largest during the inclination process of the building.Tensile force is the greatest,and the floor is under the greatest pressure at 0.2L on both sides of the middle of the floor(L is the length of the floor);the rectification and reinforcement range of large chassis building should be from the edge of the foundation to the middle of the chassis floor.Based on the analysis results,the optimization scheme of filling foundation treatment is put forward: the filling foundation should be treated by rigid piles.(3)The compressive deformation characteristics of filling and lime soil under confining pressure are studied by three-dimensional test instrument.The correlation between the compressive modulus of filling and lime soil and confining pressure(foundation depth)is revealed,and the formula for calculating composite modulus is modified.Finally,the settlement calculation method of composite foundation of filling lime-soil pile is put forward.The engineering example proves that this method can improve the settlement of composite foundation better.The accuracy of calculation.(4)Sleeve valve tube grouting technology can rectify and reinforce the large chassis building without destroying the original building structure.The inclination rate of the building is returned from 8.6 before rectification to 2.5.However,attention should be paid to controlling the grouting amount and strengthening the deformation monitoring of the building in the stage of compaction and foundation rectification.