Effects of the Plane Strain Ratio and Wall Relative Stiffness on Deep Excavation Behavior in Clay Deposits

This study presents a three-dimensional (3D) finite-element (FE) parametric investigation of deep excavations in clay deposits, focusing on the influence of excavation geometry and wall stiffness on deformation behavior. Using 100 3D FE analyses based on the Sukhumvit Metropolitan Rapid Transit Station top-down excavation in Bangkok, the study evaluates a range of diaphragm wall dimensions, including excavation width, length, wall thickness, and embedded depth, to investigate their influence on wall deformation. The findings indicate that, for wider excavations, plane strain ratio (PSR) values near unity indicate that the central area aligns more with plane strain conditions, whereas significant 3D effects remain near the excavation corners. Increasing diaphragm wall thickness mainly reduces the magnitude of lateral wall movement, whereas excavation geometry governs the spatial distribution of PSR values and corner effects. Wall embedment depth also significantly influences excavation behavior, with insufficient embedment leading to irregular responses associated with soil heave and reduced system stiffness. The PSR charts developed in this study indicate that similar PSR relationships may apply within certain ranges of wall thickness and embedment depth under Bangkok clay conditions, although deviations may occur for thicker walls or insufficient embedment. Furthermore, an analysis of the relative stiffness ratio ( R ) indicates that relationships between system stiffness, wall movement, and factor of safety depend on diaphragm wall geometry, suggesting that a universal correlation may not represent excavation behavior accurately. The presented relationships may still provide useful preliminary guidance for similar excavation conditions. Finally, this study highlights the importance of considering excavation geometry, wall stiffness, and 3D effects in deep excavation analysis.