Leda, Western Australia
Background
To improve the wastewater system within the City of Kwinana, WA, an existing Dalrymple Drive pump station, located at the corner of Dalrymple Drive and Djilba View in Leda, was upgraded.
In addition, approximately 3.3km of wastewater pressure main was constructed. The new pressure main starts at the Dalrymple Drive pump station site, travels north along Gilmore Avenue and ends near the intersection with Kirkus Road in Medina.
Avopiling was appointed by the principal contractor Georgiou to construct the temporary secant piled circular cofferdam which was required to enable installation of the pump station.
Scope
To improve the wastewater system within the City of Kwinana, WA, an existing Dalrymple Drive pump station, located at the corner of Dalrymple Drive and Djilba View in Leda, was upgraded.
In addition, approximately 3.3km of wastewater pressure main was constructed. The new pressure main starts at the Dalrymple Drive pump station site, travels north along Gilmore Avenue and ends near the intersection with Kirkus Road in Medina.
Avopiling was appointed by the principal contractor Georgiou to construct the temporary secant piled circular cofferdam which was required to enable installation of the pump station.
Findings/Challenges
The construction works were closely monitored to ensure that the piling works were carried out within the best possible tolerances such that the cofferdam could achieve the effective circular wall thickness which was required to ensure the stability of the wall. Any gaps between secant piles could have resulted in insufficient overlap of piles and need for temporary propping to ensure transfer of compressive forces.
The ground conditions comprised loose sand overlying Limestone at depth and a high groundwater table. The excavation was carried out dry as the limestone provided adequate water cut off at formation level.
The piles were founded in Limestone, at normally 1m below excavation level. The top of Limestone level was encountered relatively uniformly on site, at approximately 2m above excavation level.
A reinforced concrete capping beam was required to tie in the piles together and to ensure a sufficiently robust solution working in compressive hoop stress.