Abstract:To study the impact of foundation pit excavation on bridge piers and piles during the construction of new roads under the existing bridges, taking the U-groove project under an expressway bridge in Mawei District of Fuzhou as the background, a 3D elastoplastic finite element model is established by using the MIDAS/GTS software to simulate the whole process (including support construction and U-groove grouting) of foundation pit excavation. The analysis shows that the excavation of foundation pit causes the bridge piers and foundation piles to deviate along the bridge direction, and the deformation increases with the decrease of the distance between the foundation pit and the bridge pier. After the construction of U-groove structure, the soil reverse pressure effect significantly reduces the deviation value of the pier column. The maximum bending moments and shear forces of foundation piles concentrate at the middle and bottom of silt layers, and the internal force value increases with the decrease of distance from foundation pit. After the supporting piles + temporary bracing scheme is used, the deformations of pier columns and foundation piles are substantially reduced, which validates the effectiveness of the support measures. The on-site monitoring results align with simulation results, and the displacement values of piers are all below the standard limits. The engineering suggestions are that the U-shaped grooves should be located far from bridge piers or in the middle of the bridge span. The excavation in the weak soil layer should be combined with the supporting measures (i.e, jet grouting pile reinforcement + steel bracing) to control the deformation, which provides the theoretical basis and technical references for the design and construction of similar underpass projects.
