Three-dimensional m method for retaining structures and its application for top-down construction of excavations

The top-down method is widely used in construction of deep and large foundation pits under sensitive environment in soft soil areas. Although the three-dimensional finite element method based on the continuum mechanics has been gradually used to analyze and evaluate the impact of deep excavation on the surrounding environment, the elastic resistance method based on the beam-soil spring system is still used to analyze the internal force and deformation of retaining structures in engineering practice, while the traditional elastic resistance method cannot consider the influence of complex construction factors of foundation pits by the top-down construction method. Based on a deep and large foundation pit project with top-down method in Hangzhou, combined with the field measured data, the fitting formula for the equivalent horizontal resistance coefficient m is obtained through PLAXIS analysis of plane finite element and back analysis of elastic resistance method. The formula can consider the effect of the earth berm, the working pile close to the retaining wall and the creep of soft clay. A 3D finite element method for beam-spring system considering these complex factors due to top-down construction is proposed. It is shown that the calculated results of this method are more reasonable than those of the existing methods. For the deep soft clay foundation pits with top-down construction method, the creep of soils has a significant effect on the deformation of the retaining walls.