Research On Deformation Control Of A Subway Deep Foundation Pit In Hefei

The foundation pit is located on the southern extension of Hefei Rail Transit Line 3,with pipelines distributed around the excavation section.The soil of the foundation pit is mainly clay,and the soil is loose and uneven.The main rivers in the project area are Paihe.The total length of the excavation of the foundation pit is 202 meters,the depth is 17.4 meters,and the width is 25 meters.The underground continuous wall and internal supports are used for joint support.In order to effectively control the deformation of the enclosure structure,the method of segmented excavation was adopted.The two ends were excavated.The middle section was excavated after retaining the soil.The remaining soil was placed in a Fig eight shape,and the bottom of the grading section was along the length of the foundation pit.The total length in the direction is 59 meters.Based on the finite element method,the difference in the deformation of the foundation pit under the excavation mode of the section and the whole section is studied,and the simulated value and the measured value are compared.The relevant research content and the obtained results are as follows:(1)Using MIDAS GTS software to simulate and analyze the settlement and displacement under different excavation modes,and compare the obtained data,the results show that the peak surface settlement of the foundation pit under the overall and segmented excavation is 15.74 and 12.40mm,respectively,the difference between the two It is 3.34mm;the maximum horizontal displacement of the ground connecting wall is 12.35,11.43mm,and the difference is 0.92mm.By comparing the maximum surface settlement and the maximum horizontal displacement,it can be concluded that the reserved soil under the segmented excavation can restrain the deformation of the enclosure structure.(2)As the amount of soil excavation inside the foundation pit continues to increase,the horizontal displacement of the ground connecting wall under segmented excavation and the measured horizontal displacement of the ground connecting wall both show a continuous increasing trend,but the overall deformation trend is basically the same.The overall change pattern presents a bow-shaped distribution;the surrounding ground settlement does not change significantly at the edge of the foundation pit.The closer the distance to the foundation pit,the greater the amount of ground settlement,and the maximum horizontal displacement moves downward with the increase of the excavation depth.The change law of surface subsidence generally presents a spoon-shaped distribution.(3)There is a clear difference between the supporting axial force under the overall excavation and the supporting axial force under the segmental excavation.For the first concrete support,the maximum support axial force under the overall excavation and section excavation are 191kN and 165kN,respectively,and the second steel support,the maximum support axial force under the overall excavation and section excavation are 2445kN respectively And 2135kN,the third steel support,the maximum support axial force under integral excavation and section excavation are 3233kN and 2724kN,respectively.Through the comparison of the three supporting axial forces,it is shown that setting up reserved soil under the segmental excavation can slow down the change of the internal force of the supporting structure.Fig 68 table 8 reference 51...