How to manage ground and surface water during tunnel construction

A guide to implementing safe and efficient water management for your next tunnelling project

With substantial tunnelling projects currently underway in most major Australian cities, Coates Engineering Solutions is experiencing growing demand for the design and implementation of comprehensive water management solutions.

“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.

Here we consider why dewatering is particularly important for tunnelling projects, and explore the range of products that can be used to safely and efficiently manage ground and surface water during construction.

Why do tunnelling projects need water management?

During tunnel construction, large quantities of rock and soil must be removed to allow for the tunnel structure to be built. With much of this excavation work happening below the water table, large volumes of groundwater must be extracted and managed too.

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 important 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

• 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.

Choosing the right approach to water management

Two main strategies for managing water during construction to create a safe and dry environment for excavation 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 wellpoints. For particularly deep excavations, submersible pumps can extract groundwater from deep wells positioned outside the excavation perimeter, temporarily lowering groundwater below the tunnel.

A range of factors should be considered to find the right water management approach:

• 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 water management strategies that are required.

• 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 you can install. 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.

Choosing the right water management equipment

Coates Engineering Solutions works closely with customers to design solutions tailored to meet the unique water management needs of tunnelling projects. The team draws on one of Australia’s largest fleets of pumps and water treatment equipment, comprising:

• Diesel and electric sump pumps

• Hydraulic and electric submersible pumps

• Silenced canopy pumps, suitable for use in 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.

Coates has one of Australia's largest fleets of pumps and water treatment equipment

Dry hire or comprehensive on-site support?

“For straightforward construction sites, Coates offers a range of user-friendly pumps and specialist equipment that can be conveniently delivered to 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.”

In addition to equipment hire, Coates provides you with:

• On-site support from experienced engineers and water technicians

• Easy access to engineered temporary works solutions to prevent groundwater seepage

• Detailed water flow analysis to determine the impact of dewatering on tunnel construction and neighbouring assets

• Laboratory testing to determine water quality, water treatment requirements and to confirm discharge water quality

• Lunch & Learn sessions to upskill and keep your team’s knowledge up-to-date.

To design a safe, efficient and cost-effective water management solution for your next tunnel construction project, talk to Coates today.