Effect of ground and ground model conditions on the behavior of Diaphragm Wall.-Paper

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The study examines how ground conditions and soil-model assumptions affect diaphragm-wall behavior and temporary strut loads in a top-down metro-station excavation. The site profile comprises 20 m of soft clay over stiff to hard clay and very dense sand. Analyses using WALLAP and PLAXIS 2D considered open or closed tension cracks, undrained, drained and mixed drainage conditions, and Mohr–Coulomb versus Soft Soil (Cam-Clay-type) modeling.<br /><br />Tension cracks had little effect on wall deflection, bending moment or shear when adequate lateral supports were present. However, open-crack analysis reduced the force in the uppermost strut by about 17% because it lies within the estimated crack depth.<br /><br />Drainage assumptions had a substantial effect. Modeling the stiff-to-hard clays as drained produced the greatest wall deflection and shear force—roughly 79–83% and 61–79% higher, respectively, than in the other cases—and increased upper-strut forces by 52–63%. Middle-strut loads changed little, while mixed drainage substantially reduced the lowest-strut force.<br /><br />Using the Soft Soil Model for the upper soft-clay layer increased maximum wall deflection by about 23% relative to the Mohr–Coulomb model. Bending moment was slightly higher with Mohr–Coulomb, while Soft Soil Model strut forces were 2–6% lower.<br /><br />The authors conclude that retaining-wall design should assess realistic, site-specific combinations of drainage, tension cracking and constitutive models. Mohr–Coulomb analysis can provide preliminary estimates, while the Soft Soil Model may better represent stress-dependent behavior in soft clay.

Keywords

diaphragm wall

top-down excavation

metro station

temporary strut loads

ground conditions

soft clay

tension cracks

drainage conditions

Mohr-Coulomb model

Soft Soil Model