Research On Slab Underpinning Technology Of Model Test And Numerical Simulation

While the urbanization rate is rising rapidly,the land resources are in short supply,and the sustainable development of city has been severely blocked.The underground adding story of existing buildings is an important form of underground space development and utilization,which can effectively solve the problem of shortage of urban land resources.And its key is the foundation underpinning and the soil excavation.The slab underpinning technology utilizes the proposed partial top and bottom slab of structure itself to alternately load as substituting component to achieve underground adding story,which can also save engineering cost to a certain extent at the same time,and has a very good practical application prospect.Through physical model test and ABAQUS finite element numerical simulation software,qualitatively research and study the settlement,uneven settlement of superstructure and the stress deformation of underpinning slab during the soil excavation construction process of a slab underpinning technology proposed in this paper,which can provide application reference and reference for practical engineering.The main research contents and conclusions are as follows:(1)Through the limit analysis method and numerical simulation,the compressive stability limit load of the compressed soil during the soil excavation process of the slab underpinning technology on this paper was worked out,which can provide some reference for practical application.(2)The outdoor physical model test of 1:10 was done.The slab underpinning process was divided into top slab underpinning,soil excavation under the column foundation,column lengthening,bottom slab underpinning,and soil excavation under the top slab,etc.The five processes were simulated to study and analyze the settlement of the column-foot and the strain of the underpinning slab during each process.Test results showed,the variation law of cumulative settlement of the column-foot generally shows that the cumulative settlement of middle part is greater than side part,settlement and uneven settlement difference all meet the requirements of the specification.In the model test,except for the settlement of column lengthening process reduced thanks to the column-foot happened “uplift”,the settlement of all the other steps increased;the uneven settlement difference of column-foot showed the change rule of increasing first and then decreasing,the largest uneven settlement appeared in the column lengthening process.The lengthening process of the column is the most unfavorable process for the internal force of the superstructure.The strain condition of the slab,the maximum strain is at the mid-span position of the slab,and the strain of the slab at the intermediate position is greater than ones at the side position.Uneven settlement of column-foot will also have a significant effect on the strain of the underpinning slab.(3)Through the ABAQUS finite element program,the 3D modeling analysis of the entire construction process of the slab underpinning was done.Simulation results showed,in the top slab underpinning process and the bottom slab closing process,the settlement variation of the column-foot in middle part is bigger than ones in surrounding part.While,in the soil excavation process,which are under the column foundation and the top slab process under the top slab,the settlement change value of the column-foot in the middle is smaller than the settlement change value of the surrounding column-foot.In the column lengthening process,the settlement of the column-foot is reduced;The total tendency of cumulative settlement of each column-heel show like basin-shaped.The strain distribution of the underpinning top slab condition,the maximum strain range at the mid-position of the slab,and the strain magnitude of top slab at the mid-position of the building plane is greater than ones at the side position.The finite element simulation results are consistent with the experimental results,verify its correctness.