A Novel Approach to Bracing a Piled Retaining Wall using Temporary Piled Buttresses-Paper

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The paper presents temporary secant-pile buttresses as an alternative to conventional raking props for a contiguous bored-pile retaining wall at a new arena development in Manchester. The project included approximately 200 m of retaining wall and 1,300 bearing piles. Deep, variable made ground, historic coal workings, retained heights up to about 8.4 m, and a 25 mm movement limit near utilities made cantilevering the wall impractical. Horizontal props were also unsuitable because the wall formed part of a basement.<br /><br />Nineteen perpendicular buttresses, comprising 133 piles, were installed from the original working platform alongside the retaining-wall piles. Integrated into the capping beam, they braced the wall during excavation and were later disconnected and removed. Their locations and spacing were coordinated to avoid permanent foundations and accommodate construction sequencing.<br /><br />Designers used Plaxis 2D and WALLAP to assess soil behaviour, wall response, and varying temporary and permanent prop stiffnesses. Buttress spacing was refined iteratively; final spacings ranged from 7.2 to 9.4 m. Monitoring during excavation showed maximum measured deflections of 6–12 mm across the design sections, below the 25 mm limit and generally below predictions.<br /><br />The solution reduced programme time and cost by avoiding additional temporary works and allowing earlier removal of berms. It also reduced manual-handling risks associated with installing raking props and facilitated construction of permanent works. The authors note that improved ground-stiffness testing and more detailed instrumentation could refine future designs and help explain why measured movements were lower than predicted.

Keywords

secant-pile buttresses

retaining wall

temporary works

bored piles

basement excavation

raking props

Plaxis 2D

WALLAP

ground movement monitoring

Manchester arena development