With substantial tunnel construction projects underway in most major Australian cities, effective water management is more important than ever.
“When water is involved in construction, it can increase the risk and complexity of a project. But with the right planning, equipment and expertise, water can usually be managed quite effectively, both above and below ground,” says Yang Liu, Design Manager – Water at Coates.
During tunnel construction, large quantities of rock and soil must be removed to allow the tunnel structure to be built. With much of this excavation work happening below the water table, large volumes of groundwater must also be extracted and managed.
Often, a steady supply of water is also needed to cool the equipment used for tunnel boring, drilling and blasting. Recovering and treating the wastewater from these activities is another crucial aspect of water management for tunnelling projects.
If water isn’t effectively managed during tunnel construction, it can seep into the excavation, increasing the risk of flooding and soil erosion; reduced stability that can lead to sinkholes and collapsed tunnel entry and exit points; and reduced structural integrity of the constructed tunnel and other nearby structures.
“These and other water management issues can also affect the safety of people working in that environment and lead to construction delays and budget overruns – making water management essential to the success of any tunnelling project,” says Yang.
Two main strategies for managing water during construction include using water extraction methods for dewatering and establishing physical barriers to prevent groundwater infiltration.
Dewatering involves using pumps to extract water from sumps or a combination of vertical and horizontal well points. Submersible pumps can extract groundwater from deep wells outside the excavation perimeter for particularly deep excavations, temporarily lowering groundwater below the tunnel.
Factors to consider when determining the right water management approach include:
- Ground conditions: Water flows easily through soils like sand, gravel and silty sands and more slowly through rock, clay and silty clay. This permeability affects the soil retention properties for excavation and the required water management strategies.
- Size and depth of excavation: The groundwater level, size and depth of the excavation are important factors that shape the water management requirement. “The more you need to dig, the more water you will encounter and the greater the water management requirement for your project,” says Yang.
- Accessibility: The accessibility of the tunnel excavation sites determines how, where, and what type of dewatering equipment can be installed. The distance that extracted water needs to travel to exit the excavation is another factor shaping the design of water management solutions for tunnelling projects.
- Discharge requirements: Chemical treatment and filtration processes may be required depending on the quality of the extracted water, the discharge location and the local environmental requirements for water management. Additional environmental requirements may apply for tunnelling in urban environments to limit the impact of construction noise and water pollution.
Coates Engineering Solutions works closely with customers to design solutions tailored to the unique water management needs of tunnelling projects.
The team draws on one of Australia’s largest fleets of pumps and water treatment equipment, including diesel and electric sump pumps, hydraulic and electric submersible pumps, silenced canopy pumps suitable for residential areas, sediment filtration tanks, and chemical treatment plants. Remote monitoring systems, with telemetry-enabled pumps programmed to issue alerts if water pressure and flow rates fall outside of the required range, are also available.
“For straightforward construction sites, Coates offers a range of user-friendly pumps and specialist equipment that can be conveniently delivered to the site, allowing customers to oversee their own water management,” says Yang.
“For more complex sites, our products are backed by a team of geotechnical engineers, technicians and licensed drillers who can design, supply and install a comprehensive water management solution,” he adds.
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