Design of Deep Vertical Circular Diaphragm Wall Using Finite Element Analysis-Paper

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The paper presents the design of a deep, 36 m diameter circular diaphragm-wall shaft excavated to 82.5 m, using PLAXIS 2D axisymmetric finite-element analysis in accordance with Eurocode 7. The model simulated staged excavation and dewatering through layered fill, marine clay, residual soil, and weathered and stronger rock. Analyses assessed both serviceability and ultimate limit states.<br /><br />The wall was modelled in two ways. Isotropic analysis represented uniform stiffness and was used to estimate maximum hoop forces. Orthotropic analysis reduced circumferential stiffness tenfold to represent discontinuities between wall panels; this case governed bending moments, shear forces, and deflections. The calculated maximum serviceability deflection was approximately 92–93 mm. Orthotropic modelling increased bending moments by more than five times in one design combination and reduced hoop forces by roughly 25–35% compared with isotropic modelling, demonstrating that panel behaviour can substantially change how loads are carried.<br /><br />Earth pressures from the finite-element analysis agreed reasonably well with the analytical solution of Kim et al. (2013). Both approaches showed peak pressure at about 40–42 m depth and a subsequent decrease, consistent with soil arching.<br /><br />The authors conclude that axisymmetric finite-element modelling is effective for designing deep circular excavations, provided both isotropic and orthotropic behaviour are considered. They note that the adopted tenfold stiffness reduction was conservative; the realistic reduction depends on wall-panel construction.

Keywords

diaphragm wall

circular shaft

PLAXIS 2D

Eurocode 7

finite element analysis

orthotropic stiffness

staged excavation

dewatering

soil arching

earth pressure