TUNNEL TIME…

More time, planning for tunnel projects key to functional cities

As traffic density continues to increase with population, keeping society from grinding to a halt often rests on tunnel infrastructure says Matt McLean, operations manager for the civil and mining division at Mainmark.

He says that tunnels help to alleviate congestion, promote smoother traffic flow, and minimise disruption in built-up areas and are a highly valued element when developing urban environments, which is why a number of tunnels have been included in the national infrastructure boom, such as the new Sydney Harbour tunnel in New South Wales and the North East Link project in Victoria. “These important infrastructure projects are particularly valuable for major cities in growing metropolitan areas. New South Wales, for example, saw 5,892,206 motor vehicles registered in 2020 according to the latest motor vehicle census, with many of those vehicles expected to travel through Greater Sydney,” says McLean.

“Tunnels are complex structures that require funding in areas which can sometimes be overlooked, yet the investment is essential to ensure the safety, quality and longevity of these heavily utilised transport corridors.”

Tunnel infrastructure and ground condition relationship

When surrounding ground conditions have not been fully considered during construction, says McLean, tunnels can become more susceptible to degradation. For example, unconsolidated soil can result in a soft and often precarious envelope for tunnels that is prone to shifting.

“This can be problematic in areas such as Sydney, where ground conditions are rife with water tables, palaeochannels and weak and unconsolidated sandstone. If these geological occurrences are not identified and planned for in advance, they can affect a tunnel’s structural integrity by causing ground movement and cracking, or significant water ingress that can slowly degrade the structure.

“Unfortunately, costly and irreversible damage may not appear for some time as significant deterioration can take a decade or more.”

In some cases, issues may even be completely overlooked due to competing priorities such as meeting the community’s expectation to complete a tunnel quickly to alleviate serious traffic congestion.

“Yet the serious implications of water ingress in tunnel infrastructure cannot be ignored and having a plan and budget in place for proactive mitigation, like waterproofing and ground reinforcement to minimise the likelihood of costly structural issues post-construction, is essential.”

Remediating problems before they occur

“With increasing pressure on roads in our expanding urban centres, the need for tunnel infrastructure across Australia will be ongoing. It is therefore vital that tunnel construction includes a combination of careful pre-construction planning, ground and risk analysis, and the specification of appropriate remediation solutions. Detailed planning, site surveying and a thorough geotechnical analysis of the surrounding ground conditions should take place well before construction begins.” McLean says thus should then be followed with tailored solutions like specialised resins, gels and coatings that are engineered for civil infrastructure use, introduced before and during the tunnel construction phase.

“Based on the experience of Mainmark’s technicians with remediating and strengthening tunnels, understanding what solutions and application techniques to use for different tunnel systems and ground conditions is vital to mitigating potential issues. By utilising the right solutions, we can ensure the quality and longevity of Australia’s existing and future tunnel infrastructure for decades to come.”

“Tunnels are complex structures that require funding in areas which can sometimes be overlooked, yet the investment is essential to ensure the safety, quality and longevity of these heavily utilised transport corridors.”