Publication Abstract

DFI-PFSF Piled Foundations & Ground Improvement Technology for the Modern Building and Infrastructure Sector, (DFI and PFSF)

Design of a Raft Assisted Piled Foundation for a High Rise Prefabricated Hotel Structure in Perth, WA
Lucie Spencer and Craig Butterworth

This paper presents the design of a raft enhanced pile group recently constructed for a hotel development in Perth, WA. At the time of construction in 2016 the hotel was the tallest prefabricated hotel in Australia. The structure covers the entire 12 m by 32 m development footprint, located in an inner city environment, and directly surrounded by existing structures. The small site and lack of space required innovative thinking in terms of the substructure design. The ground conditions comprise a layer of medium dense sand underlain by variable layers of stiff clay, silts and sands. Groundwater was around 1.5 m below ground level. The substructure design was carried out on the basis of a raft enhanced pile group. This allowed the use of much shorter piles than a conventional pile solution, thereby permitting the adoption of CFA piling techniques. This also allowed the raft thickness to be reduced to such that the substructure works were maintained above the groundwater level. The design was carried out in general accordance with the Australian Standard AS 2159 and using conventional piled raft design techniques involving iteration between elastic soil settlement software and structural analysis software until spring reactions were obtained with convergence of the two models. Following this springs were introduced to model piles in the structure. Due to the variable nature of the ground and resulting uncertainty in pile base capacity it was not considered appropriate to design the system as a pile assisted raft with piles loaded beyond their ultimate geotechnical design strength. As a result, all piles were designed based on a maximum load maintained within the elastic response region, with the majority of the load taken by the piles. However, the combined capacity of the raft and the piles allowed for a saving in pile lengths and numbers of around 40%, when compared to a conventional pile group designed in accordance with the Australian Standard AS 2159. The raft slab was monitored during construction in order to check the actual displacements against the design displacements. At the end of construction, the settlements were found to be within 2 mm of the design values

 article #2580; publication #1032 (IC-2017)