A study has raised concerns that 15 miles of tunnel under Minneapolis will require $75 million in repairs, in order to safeguard against failures due to heavy rains.
With some of the tunnels greater than 100 years old, many were built using un-reinforced concrete or masonry. Increased runoff and heavy rains are creating pressures the tunnels weren’t designed to withstand.
Talking to local press, Leonard Krumm, an engineer with CNA Consulting Engineers who has just finished a six-year study on the tunnels’ condition, said excessive water pressures had cracked or burst tunnel walls in some places. If this leads to a failure or partial blockage, there is a real risk the stormwater could back up and flood the area the tunnel was built to protect.
The city of St Paul is reportedly spending $10 million to fix cracks and breaches in concrete tunnels under its remit. At one fracture, water wore an opening 88.5ft (27m) long and 19.7ft (6m) high. Two workers engaged in these works were drowned last July after they were stranded underground during a deluge.
