Design of a Raft Assisted Piled Foundation for a High Rise Prefabricated Hotel Structure in Perth, WA-Paper

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The paper describes the foundation design for a 17-storey prefabricated hotel on a highly constrained 12 m × 32 m site in central Perth. Existing neighbouring buildings, shallow groundwater, and variable ground conditions made conventional piled, pile-group, and raft solutions impractical or inefficient. The ground comprised dune sands over interlayered clays, silts, and sands, with bedrock at about 31 m depth.

The engineers selected a <strong>raft-enhanced pile group</strong>: a raft supported by 40 short, 750 mm diameter continuous-flight-auger (CFA) piles. Unlike a pile-assisted raft, this approach kept both raft and piles within a largely elastic response range, avoiding reliance on uncertain pile-base capacity and limiting settlement—important for the prefabricated structure. The shorter piles also enabled a thinner raft and avoided dewatering.

Design followed Australian Standard AS 2159. Geotechnical settlement analysis and structural modelling were iterated until their settlement profiles converged; pile springs were then incorporated into the structural model. The design predicted about 15 mm maximum settlement under working loads, with differential settlement limited to 8 mm. Construction monitoring recorded 6–10 mm settlement, within 2 mm of predictions.

Compared with a conventional rock-socketed bored-pile design, the combined foundation reduced pile lengths and numbers by approximately 40%, lowered construction costs, and shortened the programme. The authors note that more extensive monitoring and three-dimensional soil–structure interaction modelling could improve future designs and potentially reduce pile quantities further.

Keywords

raft-enhanced pile group

prefabricated hotel

foundation design

continuous-flight-auger piles

settlement analysis

soil-structure interaction

Australian Standard AS 2159

differential settlement

shallow groundwater

central Perth