Uncoupled Limit Equilibrium Analysis of Embedded Walls-PPT Presentation

PPT Presentation

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The presentation describes an uncoupled limit equilibrium (LE) method for preliminary analysis of embedded walls, such as diaphragm walls, drilled-shaft walls, and heavy sheet piles used for slope stabilization or grade separation.<br /><br />Conventional LE analyses may model a slip surface as continuous through the wall, implicitly assuming the wall shears like soil and that strength is mobilized simultaneously along the entire surface. This can misrepresent the behavior of stiff structural elements, which are more likely to be pushed into the soil in front of them, potentially causing excessive displacement or structural shear and bending failure. LE analysis alone cannot assess wall shear, moment, or deflection; those require soil–structure interaction analysis, such as finite-element, finite-difference, or p–y methods.<br /><br />In the uncoupled approach, the critical slip surface ends at the wall. The wall’s lateral capacity is set to zero in the LE model, and soil below the excavation line in front of the wall is omitted. Its resistance is represented instead by an upslope line load equal to an “allowable passive pressure” resultant—full passive resistance reduced by a factor to limit wall displacement. The method searches for the slip surface that meets the target global factor of safety while accounting for this reduced passive resistance.<br /><br />The presentation illustrates estimating the allowable passive force from the full passive force and an assumed acceptable displacement. Once the required capacity is established, a trial wall must be checked using numerical soil–structure interaction analysis to confirm acceptable displacement and structural shear and moment demands.<br /><br />The author concludes that uncoupled LE analysis better reflects the behavior of embedded walls than analyses with slip surfaces passing through them. It can support preliminary design and provide input to more complete analyses, but does not replace structural and soil–structure interaction checks.

Keywords

uncoupled limit equilibrium

embedded walls

diaphragm walls

drilled-shaft walls

sheet piles

slope stabilization

grade separation

allowable passive pressure

soil-structure interaction

finite element analysis