Design and Construction Aspects of Foundation Strengthening Works for Kununurra Diversion Dam, Western Australia-Paper

Paper

Pdf Summary

Kununurra Diversion Dam, built in the early 1960s in Western Australia, has experienced seepage beneath both abutment embankments since the reservoir was first filled. Away from the central concrete dam, the embankments transition from rock foundations to alluvium. Assessments found that coarse alluvial soils could liquefy during a major earthquake, while fine-grained soils could undergo cyclic shear failure. Backward erosion piping through medium alluvium was also considered possible.<br /><br />Remedial works were designed to improve seismic stability and control seepage. On the left abutment, a downstream weighting berm, founded partly on a cut-off trench and fitted with filters, was used to collect seepage, reduce piping risk and resist lateral spreading. On the right abutment, deep bedrock and site constraints made a cut-off trench impractical. Instead, stone columns strengthened the alluvium beneath a weighting berm. A secant wall of vertical sand filter piles beneath the berm’s downstream toe provides seepage control.<br /><br />Dry-method vibro stone columns were installed using a crane-hung system, with stone consumption and vibrator power monitored throughout construction. A successful four-column trial allowed the design to use 1.0 m columns on a wider grid, reducing the required column count by 230 while maintaining the target ground-improvement ratio. The filter piles were installed in temporary casing, with installation depths and sand quantities checked against design requirements. Test pitting found shallow rock at one end, where a sand-filled trench replaced the planned piles.<br /><br />The combined berms, ground improvement and filter systems were developed to address the dam’s identified seepage, piping and earthquake-related stability risks.

Keywords

Kununurra Diversion Dam

Western Australia

seepage control

abutment embankments

earthquake stability

liquefaction risk

backward erosion piping

stone columns

weighting berm

sand filter piles