Supporting behavior evolution of ultra-deep circular diaphragm walls during excavation: Monitoring and assessment methods comparison

Abstract

Ultra-deep circular excavations present unique challenges in geotechnical engineering due to their complex behavior and the scarcity of relevant case studies. This paper presents a comprehensive study on the excavation behavior of the deepest circular excavation (77.3 m) ever built in China through field monitoring and computational methods. The excavation process leads to the transformation of the underground diaphragm walls into an elliptical cylinder shape, elongated in one direction and shortened in the perpendicular direction. The outer annular reinforcement primarily experiences compressive stresses, while the inner annular reinforcements undergo tensile stresses, attributed to the spatial deformation of the cylinder structure. The findings emphasize the significance of considering 3D deformation and accurate characterization of internal forces to ensure the structural integrity and stability of such complex geotechnical systems. Three computational methods, including the 2D load-structure method, the 3D load-structure method, and the stratum structure method, were employed to analyze the deformation and internal forces. Comparison between measured data and calculated results reveals differences and highlights the effectiveness of the 3D load-structure and stratum structure methods in capturing the observed behavior. The study contributes to the understanding of circular excavation for designs in geotechnical engineering.