Client: Power and Water
Contractor: BMD Constructions
Project Value: $15.40 million
Leanyer Sanderson Stabilisation Ponds treats 1.5m litre of wastewater everyday. The inlet facilities filter out large objects and pollution at beginning of the wastewater treatment process. The inlet upgrade works aims to improve the performance of the ponds, reducing the environmental impact and improve the treatment of odour at the site.
Goeinventions were engaged by BMD Constructions to provide the design and certification for the temporary retention and excavation for the new proposed waste stabilisation pond (WSP) inlet works at Leanyer wastewater treatment plant (WWTP). The proposed development is to construct a new inlet pipe and other associated infrastructure on an existing pond embankment. The excavation will be required to a maximum depth of approximately 4.8m below the current pond surface level.
To retain the old pond dam wall which consists of compacted clay sandy gravel fill and soft clay,m original geotechnical information indicated no groundwater ingress and better soil conditions, however during excavation, soil conditions indicated soft clay with leakage of water through the clay lined pond wall.
Geoinventions opted to design two sheet pile retaining wall to retaining the fill based on the current soil conditions and groundwater ingress experienced. Due to the depth of soft clay experienced, the design required 7.0m long L755 profile sheet piles installed at the pond wall crest. Another challenge experienced was the high intensity rainfall events which occurred during construction which increased the softening effects of the soft clay and increased pond water levels.
Due to the criticality of the project and varying conditions, Geoinventions managed project construction and design risk by having a full time experienced geotechnical engineer on site to coordinate the installation of sheet piles. Trigger levels and constant monitoring of the sheet pile wall following heavy rainfall events gave greater confidence to BMD and their clients.
The project was successfully completed without failure to the pond wall or risk to construction personnel.