Broadbeach Dewatering & Water Treatment QLD

Iris Built has undertaken to build a monumental construction project on Broadbeach, Victoria & Albert. As part of this, the project required a 6 level basement over 4385square meters in size. The lowest excavation will be 20m below sea level (-20mAHD). Currently the excavation is to the 6th basement level and the remaining lift pits are all that remains to complete the excavation. Iris Built was commissioned to undertake a significant excavation project that required effective groundwater management, focusing mainly on the dewatering process due to potential groundwater inflow challenges indicated by the geotechnical analysis. NPE was tasked with providing dewatering services to manage an initially estimated maximum groundwater inflow of 60 litres per second (l/s), ensuring the site remained dry and compliant with construction requirements.

Project Challenges

This is one of the more complex deep excavation dewatering projects undertaken. The lowest excavation requires removing all of the material above the indurated layer (clay separating 2 aquifers). This means dewatering in 2 aquifers simultaneously, ensuring depressurisation in the lower aquifer to prevent heave in the clay layer, and capturing all of the water in the strata directly above the impermeable clay. The water quality in the excavation has provided challenges in being highly saline and containing a great deal of dissolved iron. This requires complex management of pipe scale and a high attention to detail in chemical dosing to provide compliant water discharge.

pH management through the life of the project has switched from Alkaline to acidic. Due to the different water present at different levels the water treatment, which initially had to dose to lower the pH has moved to raising the pH. Managing this change in raw water quality while consistently maintaining ideal discharge pH is a testament to our water treatment team. During the excavation a once in a generation storm event hit the worksite providing an immense amount of rainfall. Our system managed to keep up with the increased load to maintain a dry site. beyond this our telemetry experts provided immediate technical support to keep the levels visible to our team and the client even while their own home was without power.

Solutions Provided

Through the project we have maintained an open dialogue with Iris Built to keep the project moving and quickly respond to changing conditions. We have provided the following; Initial dewatering through a spears system Installation commissioning and operation of a deep well system including a double ring main to provide redundancy and peace of mind A novel solution to minimise the quantity of irons in the water by installing inflatable plugs at the clay layer through the initial phase of dewatering until the project required deeper drawdown. A combination of deep well dewatering and spears at the lowest level of excavation to deal with perched water close to the clay layer. A modular water treatment system that has allowed us to remove equipment in preparation for the tower crane install after the full drawdown was achieved. Our dewatering has achieved a dry site through the excavation. By listening and responding quickly to site condition changes and client requirements we have maintained minimal impact to site activities, allowing for the works to proceed unhindered. The dewatering project for Iris Built highlighted the critical nature of proactive groundwater management in construction. With NPE's robust planning, the project adeptly navigated the complexities of potential groundwater inflows while ensuring compliance and safety. This case underscores the importance of comprehensive planning and flexibility in project execution to address the varying demands of construction environments effectively.