Staged Construction of an Interstate I69 Embankment: Coupled Hydro-Mechanical Numerical Simulation-Paper

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The study evaluates staged construction of an Interstate 69 embankment over highly compressible soft clay in southern Indiana. The embankment, which serves as a bridge approach, was built on deposits extending to about 75 ft deep. Staged loading was used to limit instability by allowing excess pore pressures to dissipate and effective stress—and therefore undrained shear strength—to increase between construction stages. Wick drains, installed in a triangular pattern at 5-ft spacing, accelerated consolidation.<br /><br />The authors developed a two-dimensional, fully coupled hydro-mechanical finite-element model in PLAXIS. It represented the as-built embankment, soil layers, drainage, construction sequence, waiting periods, and temporary surcharge. Foundation clays were modeled with the Hardening Soil constitutive model, with parameters informed by extensive site investigation, laboratory testing, CPT data, and published correlations. Instrumentation—including settlement plates, extensometers, and piezometers—provided field measurements for comparison.<br /><br />Predicted surface and subsurface settlements and excess pore-water-pressure development and dissipation generally agreed well with observations during construction. Settlement predictions were within a few inches of settlement-plate measurements, and the model captured settlement trends across loading and waiting periods, though it underpredicted settlement in one clay layer. Pore-pressure predictions were also reasonable; pressures near shallow bedrock were overestimated, likely because the model treated the bedrock as impermeable.<br /><br />The authors conclude that staged construction is effective for improving foundation stability, while reliable modeling depends on comprehensive site investigation, careful parameter selection, and an appropriate constitutive model. They also recommend conducting pore-pressure dissipation tests during CPT soundings to better establish groundwater conditions and estimate in-situ permeability.

Keywords

staged construction

Interstate 69 embankment

soft clay

finite-element model

PLAXIS

wick drains

consolidation

pore-water pressure

Hardening Soil model

settlement measurements