2D and 3D Finite Element Analyses for Cantilever Slurry Walls in Cohesionless Soil-Paper

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The study compares two- and three-dimensional finite element (FE) analyses of 6 m-deep square excavations supported by cantilever slurry walls in dry cohesionless sand. It examines how excavation length-to-depth ratio (L/H), wall modeling assumptions, capping beams, and excavation geometry affect wall deflections and bending moments.<br /><br />In 3D analyses, wall deflections and bending moments approached plane-strain results as the excavation became longer. For conventional square excavations, discrete-panel wall models reached approximately 90% of plane-strain deflection and 95% of plane-strain bending moment at L/H = 5. Thus, excavations with L/H above 5 largely resemble plane-strain conditions. Modeling slurry walls as continuous isotropic plates substantially underestimated responses. Discrete panels provided the most representative model; a continuous plate with lateral-to-vertical stiffness ratio no greater than 0.001 was a practical alternative.<br /><br />Capping beams reduced wall deflections and redistributed bending moments, including the development of negative moments. Their influence extended through the wall depth and was especially significant at low L/H ratios, so it should be represented in 3D analysis when relevant.<br /><br />The study also considered a 270° excavation geometry, representing a corner where most surrounding soil is excavated. For L/H ratios above 3.5, predicted deflections exceeded plane-strain values. Because plane-strain analysis could therefore underestimate deflections and bending moments, potentially producing an unsafe design, 3D effects should be considered for this geometry.<br /><br />Overall, the findings show that 2D analysis is not uniformly conservative. Selecting an appropriate model requires attention to excavation geometry, wall panel behavior, and capping-beam effects.

Keywords

finite element analysis

square excavation

slurry wall

cantilever wall

plane-strain conditions

wall deflection

bending moment

capping beam

three-dimensional analysis

excavation geometry