| The technology of adding underground floor is a method to expand the use space of the underground structure of the existing building from top to bottom.It is in line with the concept of green environmental protection,and the functional upgrading and comprehensive transformation of existing buildings are in line with the national industrial development direction.However,at present,there is no systematic achievement and complete set of technical standards or construction specifications in the excavation technology of underground additional layer,which has great subjectivity and experience in this field.Therefore,it is very important to carry out the model test of pile foundation underpinning method.In this paper,through the design of model test and combined with the finite element three-dimensional numerical simulation to study the influence of pile foundation underpinning construction on the settlement and deformation of existing buildings,the main research contents and results are as follows:(1)In order to study the settlement rule of pile foundation underpinning and the change rule of frame beam strain more comprehensively,the model test of 1:10 is adopted.The existing buildings in this test adopt reinforced concrete structure.Considering the possibility of model construction,only the main beam is poured,not the secondary beam is designed,and the basement floor and roof are not poured;pile foundation underpinning is adopted for underpinning;the excavation method adopts circular excavation and reservation core local law.(2)In the test,the three working conditions of soil excavation under corner column,side column and middle column are taken as a cycle,which are divided into three cycles and nine working conditions to study the law of settlement and deformation.Collect the settlement value of each column base and the strain value of the second and third floor frame beam span under different working conditions,study the influence of earthwork excavation on the existing structure,and draw the conclusion that the settlement value of column base under working conditions 1,4 and 7 is generally larger than that under other working conditions and presents "basin type settlement",and the rebound amount of foundation soil in the middle span after earthwork excavation in working conditions 3 and 6 is large,and the upper structure presents "upward arch" trend;the frame structure has a "upward arch" trend In the first excavation,the strain changes most obviously.(3)ABAQUS is used to establish a solid three-dimensional model.According to the above nine working conditions and the construction of basement floor and roof,the construction process of pile foundation underpinning reverse construction method is modeled.By comparing the calculation model with the model test,it is verified that the calculationmodel can accurately simulate the settlement and deformation laws obtained from the model test,so that the 1:1 calculation model can be used to simulate the actual project and collect the data,The corresponding settlement and deformation values verify the feasibility of this underpinning and excavation method.Through the 1:10 model test and the 1:10 and 1:1 numerical simulation,this paper studies the settlement of the column base,the change rule of the frame beam strain and the influence of the basement floor and roof construction on the settlement of the existing building in the construction of the pile foundation underpinning reverse method,so as to provide a reference for the actual project application. |
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