Study On Model Test Of Pile-Wall Foundation Replacement Of Underground Adding Layer In Existing Buildings

With the acceleration of urbanization and the increasing shortage of urban land,the rational development and utilization of underground space resources is an effective way to solve the urban land shortage.At present,although some scholars have proposed and studied the development and utilization of underground space for existing buildings,they have not formed a set of technical standards,and most of them are carried out by numerical simulation,which has strong subjectivity and experience.Therefore,it is very important to carry out the experimental research on the model of the existing building overburden model,to explore the law of the settlement and deformation of the existing building,and to provide the reference basis for the actual engineering project of the existing building's underground overburden.Based on the physical model test and ABAQUS 3D numerical simulation,this paper makes a comprehensive study on the existing building's underground overburden project with strip foundation,hoping to provide technical support for underground space development and utilization.The main research contents and achievements are as follows:(1)In view of the project of underground layer-increasing of existing frame structure with strip foundation type,this paper puts forward the concept of "pile-wall" type foundation support replacement,using layered and zonal earth-excavation method to carry out earth-excavation so as to achieve the purpose of new underground spaceBased on this,the1:10 scale model test was designed,and the settlement of the column foot and the strain of some beams and columns were monitored during earthwork excavation.The model test shows that the settlement and non-uniform settlement of the foot of the column increase greatly compared with other excavation conditions after the completion of the second step of earth excavation.In the process of earthwork excavation,the maximum strain of the third layer beam is always greater than the maximum strain of the second layer beam,and the third layer beam should be monitored emphatically during construction;in the stage of earthwork excavation,the settlement of column foot,uneven settlement,beam and column strain values are all very small.(2)Numerical simulation of the model structure at 1:10 shows that: At the foot of the model structure,the settlement law of "saddle shape ",the settlement law of " U shape " and the settlement law of " basin type " are presented.The maximum settlement of the foot of the model structure is 3.0 mm,the maximum settlement of the foot of the column is 3.6 mm,the settlement of the foot of the column is close,and the maximum change of the settlement of the foot of the column is the first layer of intermediate soil in excavation,and the settlement law of the foot of the column under the other working conditions is more consistent.(3)The 3D numerical simulation of the prototype frame structure shows that:hesettlement law of column foot is similar to that of model structure numerical simulation column foot,of the model structure,and is in good agreement with that of the experimental column.In the earth excavation stage,the maximum change of settlement occurs at working condition 2.When the third layer of intermediate soil is excavated,the springback deformation of foundation pit causes the settlement of column foot to decrease relative to the previous working condition,and the final settlement meets the requirements of relevant codes.When the basement floor and roof are constructed,the settlement of column foot increases significantly,and the rebound deformation of foundation pit is effectively controlled.with the increase of excavation depth,and when the soil is excavated on both sides,the springback deformation of foundation pit is small,and when the middle soil is excavated,the springback amount of foundation pit is large.