The paper, co-authored by Senior Geotechnical Engineer Alireza Akoochakian and Principal Geotechnical Engineer Phil Band, presents a case study evaluating impact rolling as a ground improvement method for a commercial development site characterised by highly variable fill, granular layers, and soft to firm cohesive soils.
The team sought to improve near-surface ground conditions sufficiently to support shallow foundations, avoiding the higher costs and construction impacts associated with deep foundations. Impact rolling was applied progressively in multiple passes using heavy dynamic loading across five treatment areas and assessed through pre- and post-treatment Cone Penetration Testing and Dynamic Cone Penetrometer (DCP) testing, settlement monitoring, and proof rolling. Results showed that impact rolling was effective in granular soils, producing significant densification, increased stiffness, and settlements of up to 200 mm, with improvements largely confined to the upper 1.5–2.0 m of the subgrade. However, fine-grained cohesive soils (clays and silts) demonstrated limited and inconsistent response, requiring supplementary remediation such as excavation and replacement with engineered fill in localised soft zones.
The study concludes that impact rolling is a valuable but soil-dependent ground improvement technique, best applied as part of a flexible, site-specific strategy supported by detailed verification testing to ensure performance and manage residual settlement risks.
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