Researches Of Numerical Simulation And Measured Datum Of Excavation Deep Foundation Pit Under-acrossing Existing Lines

The Ningbo station is reconstructed by mean of digging deep excavation under the existing railway, it is a large transportation hub which provides vertical transfer for national railway passenger flow distribution and urban rail transit system. In the construction, a temporary railway bridge is build to step across the deep foundation pit to ensure the regular and safe operation of the existing main line. To achieve this, the pillar pile vertical supporting lattice column and the new structure form of continuous girder bridge will be used. This study is meaningful for it explores the deformation and force analysis of bridges under different excavations. The monitoring data of deep excavation beneath existing railway and the MIDAS/GTS model are theoretical foundation for analyzing deformation of retaining structure, stress of the supporting structure, temporary deformation of railway bridge, upheaval and settlement deformation of pillar, and stress of beam bending. Still, this thesis will explore the relative factors which influence the horizontal and vertical displacement of the temporary railway bridge in this program. The main research contents and research results are as follows:(1) According to the characteristics of the reconstruction project of Ningbo station, this study develops monitoring programs for the deep excavation beneath existing railway and the temporary railway bridge. They determine the monitoring items, equipments, frequency, sites, etc. which should guarantee timely feedback and informational construction.(2) It analyzes and explores the horizontal displacement of deep foundation pit on the base of existing main tracks, horizontal displacement of the top of the building envelop, sinking of the outside slope, sinking of the pillar; three-dimensional displacement of the temporary railway bridge, beam bending stress of pillar under various situation and obtains some important rules and characteristics of deformation during this kind of construction, which can be used as references in some similar practical situation.(3) The thesis also builds the MIDAS/GTS model on the base of existing railway. It analyzes the deformation of the building envelop, axial force of the supports; beam bending stress of pillar, sinking of the pillar, horizontal and vertical displacement of the temporary railway bridge. This can offer theoretical foundation for the force rules of deformation on the base of existing railway, which can be also employed as references in some similar practical situation.(4) The thesis analyses the actual and analog computation data of horizontal and vertical displacement of temporary railway bridge. According to the results, it finds the flexibility and regularity of its deformation. It explores the ways of excavation, the effects of the expansion of the inside wall and adding cross supports have on the horizontal displacement of the temporary railway bridge. Meanwhile, it explores the effects of the reinforcement of soil mass in the range of existing railway, the expansion of the inside wall and buried depth of bridge pillar, etc. have on the vertical displacement and some rules are found.