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

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This study assesses how construction of a 10 m-high highway embankment over compressible soft soils affects a nearby shared-path bridge in southeast Queensland. Three-dimensional PLAXIS modelling was used to evaluate long-term pile movements at the bridge abutment and pier, considering different construction sequences and structural configurations.<br /><br />The key comparison was between an original sequence, in which the embankment was constructed and preloaded before the bridge, and a revised sequence, in which the bridge was built first. With the revised sequence, predicted pile-head displacements at both the abutment and pier were nearly three times greater. Although redesigned foundations—adding piles and increasing structural stiffness—reduced movements by about 50% at the abutment and 45% at the pier, displacements remained higher than under the original sequence.<br /><br />The findings show that construction staging strongly influences bridge performance on soft ground. Where feasible, completing and preloading the embankment before building nearby structures is the most effective way to limit pile movements and may avoid costly foundation strengthening. The study also found that simplified models using plate and embedded beam-row elements provide reasonable initial estimates, but may predict displacements about 5 mm, or roughly 15%, higher than detailed models using volume elements. Volume-element modelling is recommended where displacement tolerances are tight.

Keywords

highway embankment

soft soils

bridge abutment

bridge pier

pile displacement

construction sequencing

PLAXIS modelling

foundation redesign

embankment preloading

volume-element modelling