Perth City Link – Wellington Street Bus Station

Background

Demolition of the old Wellington Street Bus Station has allowed for the construction of a new, Australian-first, dynamic stand-allocation underground bus station.  It forms part of the Perth City Link project, an urban renewal and redevelopment by Metropolitan Redevelopment Authority, with the intention of enhancing local vibrancy by connecting Perth city centre and Northbridge.

The ground conditions are challenging due to the variable clays and sands encountered, and high groundwater table, which are associated with a remnant lake system in the area.  Top down construction methodology was adopted with concrete columns at basement level constructed as piles from original ground level.

Scope

CMW carried out foundation pile designs, testing and construction supervision for a total of 92 piles as detailed below:

Cased bored piles, up to 1800mm in diameter and 54m depth, with 22 rock socketing into Kings Park Formation (KPF);
The piles were constructed with temporary, and in some cases, permanent casing, and under polymer fluid;
Osterberg-cell (O-cell) testing on 2 piles including design, interpretation and use of results to optimise design; and
Rock socket and pile toe clarification on site for each pile as well as general construction support.

Findings/Challenges

As the foundation designs were highly optimised, to meet the tight settlement and tolerance specifications, with large diameter bored piles under large loads and with high groundwater condition, the construction works were closely monitored. Competent rock sockets, and quality concrete were ensured with a comprehensive pile testing program.