Mechanical Behaviors of Cylindrical Retaining Structures in Ultra-Deep Excavations

Cylindrical shafts have been widely used in practice with prominent structural superiorities, primarily because of the spatial arching effects resulting from their circular retaining structures. The behaviors of cylindrical shafts were investigated via three-dimensional finite element analyses of two circular excavations for anchorage foundations in suspension bridge engineering. By comparing the FE-predicted results with the field measurements, the accuracy and reliability of the numerical models were verified. Additional calculations were also performed to study the influence factors of circular retaining structures. The following major findings were obtained: (1) The stresses in both the diaphragm walls and lining walls are relatively small, indicating that the arching effects of circular and double circular retaining structures are significant; (2) The main function of the lining walls is to enhance the rigidity of the diaphragm wall and to constrain its displacements, so the decrease in the lining wall thickness, the shape variation of the retaining structures and asymmetrical excavation make little difference to the structure stress. (3) The temperature change during circular or double circular excavation has a great influence on the stresses of the retaining structures.