In this subterranean world, one can walk seemingly endless lines of steam pipes and fiber-optic cables along smooth, grey concrete walls — interrupted only by a round-face pressure gauge here, an orange or yellow steel ladder there, or a locked metal gate.

It can be 100-plus degrees, winter or summer. Horns don’t honk, birds don’t sing, and smartphones fail. The sun never shines. Yet, this world coexists just yards from the Diag, Hill Auditorium, the Michigan Union and other campus landmarks.

It’s the mysterious university tunnel system, all six-plus miles of it. The only ones who see it are Utility Department staff, construction crews doing maintenance and upgrade work, and the occasional tour taker.

This spring and summer, construction crews will focus on a $1.8 million project to reinforce sections of the tunnel system. A recent study determined that some sections under proposed emergency vehicle access routes require reinforcement to withstand the loads of heavy emergency vehicles, particularly fire trucks carrying water tanks. Select tunnels will be reinforced with concrete and steel to allow heavy vehicular traffic.

The project calls for work along nearly 550 feet of tunnels near the School of Social Work Building and the restoration of paving and landscaping disturbed by the project.

“Utilities to nearby buildings will continue to be provided during construction. The project will require temporary detours for pedestrian traffic and emergency vehicle access, but access to nearby buildings will be maintained,” said Timothy Slottow, executive vice president and chief financial officer, in a February report to the Board of Regents.

They approved the project, with funding provided from Utilities & Plant Engineering resources. Designed by Commonwealth Associates Inc., work will begin around May 1. Completion is scheduled for this fall.

Protecting the enterprise

The key value of the tunnel system is that it houses steam lines to power heating and cooling systems, domestic hot water lines for showers, compressed air to serve mechanical systems, and fiber-optic cables to transmit data to central campus buildings.

“A steam distribution system is one of the most efficient methods for conveying energy used to heat or air condition buildings,” says Michael Swanson, utilities services manager. He has managed the tunnel system the past 15 years.

Tunnels are looped, which means that more than one tunnel serves each building.

“That’s so buildings can be backed up and fed by utilities from more than one direction. Because this is a research institution, the tunnel system is designed for high reliability,” Swanson says. “That’s why we take such pride in the work we do and why we maintain a high state of repair. It’s just critical to the research that goes on at the university to have a highly reliable steam and mechanical distribution system.”

While the reinforcement project is the focus of tunnel-related work this year, improvements and maintenance work is ongoing.

“In the past 10 years we’ve had ventilation improvements, and we’ve encapsulated all the asbestos,” Swanson says. More recent upgrades include pipe-insulation improvements, and expansion joint replacement projects to maintain the integrity of the piping systems. “We build our tunnels in such a way and go to great lengths to waterproof them so that they’ll last 100 years or more.”

The Utilities Department every seven to eight years conducts a comprehensive structural assessment of the tunnel system. This includes reviewing past reports, tracking previous repairs, and a review of the structural condition of the present system. Based on priorities, recommendations are made for the next repair cycle. The university has invested approximately $60 million during the past 15 years to refurbish and maintain the tunnel system, and plans to spend about $20 million in the next five to 10 years, Slottow says.

Tunnels history

In 1894, the first brick tunnels at U-M were constructed to protect the piping that provided steam heat to buildings around the Diag. Sixty percent of the tunnels used today were built from 1925-40, to accompany rapid building and facilities growth. Another 20 percent of the tunnel system was built in the 1950s. More tunnels have been built since to support new buildings.

“We’ve found abandoned brick tunnels as recently as five years ago,” Swanson says. They were discovered on North University Avenue. Crews looking to install stormwater piping near the Central Campus Transit Center drilled into a void and found an old abandoned brick tunnel in near perfect condition for its age. In such cases, crews fill the abandoned structure with a cement and potash mixture called lean concrete which basically acts like dirt but allows the mixture to flow like concrete, Swanson says.

There was a time when rats were known to hang out in the tunnels, near garbage containers. “It was not as well sealed up then. But we’ve removed all the penetration and we don’t have that issue today that we had over 20 years ago,” Swanson says. There is still the occasional infestation of cockroaches, for which exterminators are called.

Tunnel trespassers beware

Students in the 1980s were known to trespass in tunnels to play “Dungeons and Dragons.” Students in similar tunnel systems at other universities have been involved in fatal accidents. But Swanson says trespassing is rare today.

“Since then, we’ve added a very robust security system, all of the entrances are now locked and monitored. The U-M Police Department takes unlawful entry to the tunnels very seriously,” he says.

Police Chief Bob Neumann says utility tunnels are restricted for reasons of infrastructure security and safety.

“Persons authorized to work in the tunnels have received specialized training and follow safety protocols specific to the environment. Violators are subject to prosecution for crimes ranging from trespass to breaking and entering depending on the circumstances,” he says.

Members of the public who believe they see an unsecured utility entrance are asked to contact university police.