Saving America’s Tunnels

By Keith Armishaw, Contributing Author

America’s tunnels are strained. Between constant traffic, geological forces and environmental conditions, tunnels often require regular maintenance to remain safe and operational.

Renovating and repairing tunnels — including the process of removing deteriorating linings and wall portions — is a labor-intensive and often inefficient process. Water provides one possible solution with hydrodemolition.

Hydrodemolition is an impact-free process that utilizes a high-pressure water jet with 40,000 psi power, to remove the structure’s damaged concrete without causing underlying damage elsewhere, like steel reinforcements.

Using a robot, the process’s reduced impact eliminates vibrations that can cause microfractures — miniscule cracks in the surrounding concrete that compromise the integrity of the tunnel.  

The removal process leaves behind the optimal texture for bonding new concrete.

Hydrodemolition is a fast, accurate process that works well with the curved and complex surfaces often seen in tunnels.

A common misconception about the hydrodemolition process is that it can only be used to complete flatwork; however, manufacturers have developed components that allows it to be used on virtually any concrete surface, such as overhead, curved or vertical.

This level of precision extends the life of tunnels as strong concrete remains intact. A report from the Swedish Cement and Concrete Research Institute found that repair life expectancy for projects using hydrodemolition is 21-35 years compared to 7-12 years with mechanical chiseling.

This process was put to the test with the rehabilitation of the East Side Transit Tunnel in Providence, R.I.

First built in 1914, repair crews were able to conduct targeted repairs to the century-old arch and tunnel walls without causing damage to the overall structure.

Hydrodemolition also streamlines the process as operators can adjust the robot’s speed to remove the damaged concrete and meet specific project specifications. Robots can be set to adjust speeds to remove concrete that is deeper or shallower all in one pass, eliminating the need to stop and readjust the robot for the different removal depths.

Many contractors and engineers are deterred from using hydrodemolition because of uncertainty about how to manage water. This can be solved with the use of a fully automated treatment plant, which neutralizes pH and reduce suspended solids so the water can be safely released into the environment or recirculated through the equipment. Using recycled treated water reduces usage and costs associated with continuously bringing in fresh water.

Despite the higher upfront investment associated with hydrodemolition compared to traditional concrete removal, the long-term savings add up. Hydrodemoltion is up to 25 times faster than manual methods, requires less labor as the robots can be operated remotely by a single person and provides a higher-quality result in addition to the extended repair life.

Keith Armishaw is the business development manager for Aquajet’s North American subsidiary. He has more than 25 years of industry and leadership experience.