Is Excess Pore Water Pressure Build up an Engineering Demand Parameter for Excavation Analyses?-Paper

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The study examines whether excavation-induced excess pore water pressure can help predict ground movements and select an appropriate analysis method. Using PLAXIS 2D, the authors modeled a braced excavation in cohesive soils with fully coupled solid–fluid behavior, then varied excavation rate, soil hydraulic conductivity, and excavation geometry.<br /><br />The results show that drainage response depends strongly on the excavation-rate-to-hydraulic-conductivity ratio (ER/k) and the excavation’s width-to-depth ratio. Very low ER/k values correspond to drained behavior, while very high values approach undrained behavior; intermediate conditions are partially drained and may not be represented accurately by conventional drained or undrained analyses. The study defines the pore-pressure ratio α as excess pore pressure divided by the vertical stress relief from excavation. Together, α and ER/k provide a practical way to estimate pore-pressure buildup and determine whether a coupled analysis is needed.<br /><br />For practical purposes, settlements under undrained conditions and at ER/k above roughly 100 were generally similar. When α is below 0.2, however, settlement estimates showed greater variability, making fully coupled solid–fluid analysis advisable unless excavation proceeds slowly enough for drained conditions to apply. The authors therefore present excess pore pressure as a useful engineering demand indicator—not in isolation, but alongside excavation rate, soil conductivity, and geometry—to guide analysis selection and improve movement predictions.

Keywords

excavation-induced pore pressure

ground movements

PLAXIS 2D

braced excavation

cohesive soils

hydraulic conductivity

excavation rate

fully coupled analysis

pore-pressure ratio

settlement prediction