Assessing the Impacts of Embankment Construction Over Soft Soil on an Adjacent Bridge-PPT Presentation

PPT Presentation

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The presentation assesses how constructing a 10 m embankment over soft soils affects piles supporting a nearby bridge in Southeast Queensland. Soft clay can undergo short- and long-term vertical and lateral movement, potentially causing damaging displacement in adjacent structures.<br /><br />The site investigation included 19 boreholes, 15 CPTu tests, laboratory consolidation tests, and pore-pressure dissipation tests. The team used PLAXIS 3D consolidation analyses over a 100-year period, modelling soft and firm clays with the Soft Soil Creep Model, stronger soils with the Hardening Soil model, and rock with the Mohr-Coulomb model.<br /><br />Three scenarios were considered. In the original sequence, the embankment was built and preloaded for three months before bridge construction, allowing some ground movement to occur beforehand. Predicted displacements were considered acceptable. When the sequence was reversed and the embankment was built after the bridge, displacements increased substantially and became unacceptable. A redesigned, stiffer bridge structure was then assessed for this revised sequence; it reduced transverse pile displacements by 50% compared with the original structure under the same construction sequence. For the revised abutment, modelling with volume elements also predicted 12% less transverse pile movement than a simplified plate-and-beam model.<br /><br />The findings show that construction staging strongly influences bridge performance beside embankments on soft ground. The most effective way to limit pile movement is to build and preload the embankment, allowing consolidation before constructing the bridge. If this sequence is impractical, a stronger and more costly foundation or structural design may be necessary. Simplified modelling can provide an initial estimate, while volume-element modelling is recommended where displacement tolerances are tight.

Keywords

embankment

soft soil

bridge piles

construction staging

consolidation

PLAXIS 3D

lateral displacement

pile movement

ground investigation

foundation design