Impact from the Construction of a Working Platform and Girder Lifting Operation on Bridge Pile Foundation in Soft Soil-Paper

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The paper examines how raising a working platform and operating a heavy crawler crane affected bridge piles founded in soft alluvial soil at Pier 09 of the Nambucca River Bridge in New South Wales. The site had up to 22–25 m of soft clay above bedrock. After the piles and pier columns were built, the platform was raised by about 1.3–1.5 m to provide crane clearance. The crane’s high bearing pressures during girder lifting added further loading close to the pier.<br /><br />Surveying found that the columns had already moved 25–50 mm toward the river after the platform was raised. During the first two girder lifts, they moved a further 28–39 mm. This was broadly consistent with numerical predictions: finite-element modelling estimated free-field soil movement, and boundary-element analysis assessed pile response. The predicted column-top displacement was about 72 mm, close to the measured total of 64–78 mm.<br /><br />After the second lift, the operation was paused and a 5 m-wide rock berm was built on the riverside of the pier to counterbalance the platform and limit further movement. Subsequent lifts caused no more than about 8 mm of additional displacement. Some movement recovered after crane loading was removed. Analyses concluded that the piles had sufficient capacity to withstand both the temporary peak bending moments during lifting and the smaller residual moments expected after construction.<br /><br />The case demonstrates that a platform can satisfy stability requirements yet still induce significant movement in nearby permanent foundations on soft ground. Heavy-lift planning should therefore assess effects on existing piles as well as platform stability. The authors recommend early coordination between geotechnical and construction teams, careful movement monitoring, and an observational approach with contingency measures such as a counterweight berm.

Keywords

bridge piles

soft alluvial soil

crawler crane

working platform

pier displacement

finite element modeling

boundary element analysis

girder lifting

rock berm counterweight

geotechnical monitoring