Abstract:

Excavation of deep foundation pit may result in deformation of supporting structures and surrounding soils. These deformations have different sensitivities to different influencing factors. Taking Shanghai Yangtze River Tunnel Project as an example, this study establishes a geometrical model of the foundation pit excavation based on actual soil distributions. The finite element analysis software ABAQUS was used to simulate the excavation process of the foundation pit. Horizontal displacements of the diaphragm wall were examined during excavation. Comparison between the field monitoring data and the simulated ones was made. Three factors influencing horizontal displacement of the diaphragm wall were chosen: thickness of diaphragm wall and width/depth of narrow excavation, and for each factor tree levels were set. Thus a total of 9 numerical simulation tests were performed based on the orthogonal table L$_9$(3$^4$) using an orthogonal test technique. Range analysis and variance analysis were then made. The simulation results are close to the field monitoring data. Factors affecting horizontal displacement of diaphragm wall in a descending order are thickness of diaphragm wall, depth of excavation of narrow foundation pit, and width of excavation of narrow foundation pit. Thickness and horizontal displacement of the diaphragm wall show a positive relation, while width and depth of excavation of the narrow foundation pit and horizontal displacement of the diaphragm wall show a negative relation. The results may provide references in analyzing deformation of retaining structures in foundation pit construction.

Key words: foundation pit, retaining structure, horizontal displacement, finite element method, orthogonal test