Three-dimensional Coupled Numerical Analysis On Bearing Deformation Mechanism Of Composite Foundation With Floating-encased Stone Columns

The reinforced gravel pile composite foundation is a kind of soft soil foundation treatment technology,which is widely used in super soft soil,liquefiable soil,wetland protection area and other soft soil foundation reinforcement.At present,most of the researches on reinforced gravel pile composite foundation focus on the condition of thin soft soil and good geological condition of pile tip bearing layer.With the rapid development of economic construction,the application scope of the stiffened machete pile is further expanded.In the Guangdong-Hong Kong-Macao Greater Bay Area and the southeast coastal areas of China,the thickness of soft soil is large and the stiffened machete pile is difficult to pass through.At this time,the stiffened gravel pile is in suspension state,the pile tip resistance provided by the bearing layer is small,and its bearing deformation mechanism has changed significantly.Therefore,it is necessary for the composite foundation to adapt to the development of the new era to carry out further research on the bearing deformation mechanism of the reinforced gravel pile in deep soft soil area.Therefore,this paper is combined with the National Natural Science Foundation of China project "Research on dynamic Bearing Deformation Mechanism and Analysis Method of Reinforced gravel pile Composite Foundation"(51908150)and the Guangdong Provincial Education Department Young Innovative Talents Project "Research on Bearing Deformation Mechanism of Reinforced gravel pile Composite Foundation in Pearl River Delta deep soft soil Area"(2018KQNCX200).On the basis of the laboratory model test,the numerical model of the composite foundation with suspended reinforcement crushed stone pile is established by using the numerical analysis method of discrete element method and finite difference method.The bearing deformation mechanism and influencing factors of the composite foundation with suspended reinforcement crushed stone pile in deep soft soil area are discussed.The research content of this paper mainly includes the following aspects:(1)Gravel and geogrid in composite foundation of floating-encased stone columns are simulated by discrete element particles,and soft soil around pile is simulated by finite difference grid.The discrete element method numerical simulation tensile test and cantilever test of geogrids were established,and the test results were compared with those of laboratory tests.The bending stiffness and tensile stiffness of geogrids were calibrated,and the discrete element method simulation mesoscopic parameters of geogrids were determined.The triaxial test of discrete element method numerical simulation of gravel was established,the internal friction Angle of gravel was calibrated,and the mesoscopic parameters of discrete element method simulation of gravel were determined.The finite difference numerical simulation triaxial test of soft soil was established,the elastic modulus and ultimate bearing capacity of soft soil were calibrated,and the finite difference numerical simulation parameters of soft soil were determined.(2)Using the coupling calculation logic of discrete element method and finite difference method,the coupling numerical calculation model of suspension reinforcement reinforced gravel pile composite foundation is established,and compared with the indoor model test results,to verify the rationality and reliability of the coupling numerical model in this paper.On this basis,the stress and deformation characteristics of gravel(vertical stress of gravel,radial strain of pile,etc.),the stress variation of soft soil around pile(vertical stress,radial stress of soft soil,etc.)and the stress variation of geogrid are discussed deeply.(3)According to the four important parameters affecting the bearing deformation characteristics of the composite foundation of reinforced gravel pile,namely,the condition of bearing layer,the particle size of gravel,the depth of reinforcement and the tensile stiffness of reinforcement,the parameter analysis is carried out.The numerical analysis model of the composite foundation of floating-encased stone columns with different parameters was established to study the influence of different factors on the bearing deformation characteristics of the composite foundation of floating-encased stone columns with different parameters.