Addressing Aging Utility Tunnels at Midwestern Universities

By Myles Moran, PE, Project Engineer, RMF Engineering & David Mercer, PE, Principal, RMF Engineering

Our colleges and universities are aging gracefully, but with time, the need for updated infrastructure becomes evident. Higher education institutions are regularly addressing their physical facilities, updating building interiors and exteriors to ensure they continue to meet evolving standards and student expectations. What can’t be overlooked in these improvements is often hidden from plain sight below the surface—the tunnels that house the critical utilities enabling these buildings to function.

Underground utility tunnels play a vital role in the continuous functioning of utility services on campus such as steam, chilled water, electricity, domestic water, and telecom systems, housing and protecting the piping and cables necessary to each. They are a tremendous asset for increasing the life span of the many utilities within by allowing for regular inspection and repairs to be performed without the need for excavation and impacts to above ground operations. Like the institutions that sit above these tunnels, many were built over 100 years ago, and due to natural wear and tear are in need or will soon be in need of renovation or retrofit to remain usable for decades to come.

Without addressing these aging tunnels, the systems that service the residence halls, academic buildings, recreation centers, and other campus facilities that students, staff, and faculty interact with each day are at risk of failure, where consequences can be more far reaching than the loss of heating and cooling, or a pause in operations. Depending on the system, failure can be hazardous to those on campus and most certainly maintenance personnel, amplifying the resolve to maintain these critical pieces of infrastructure. 

Evaluating Aging Tunnels

Many of the tunnels built in the late 19^th or early 20^th century were constructed with brick walls and brick arch tops and are still widely in use today. In fact, a recent structural assessment performed on a university campus by RMF Engineering, Inc. found a stretch of brick tunnel from the 1920s in surprisingly good condition given its age. The mid-20^th century witnessed an increasing shift to reinforced concrete for reduced costs and ease of construction, which made it easier for some institutions to invest in these important infrastructure assets. Precast concrete tunnels, cast-in-place concrete tunnels, and brick-walled tunnels with cast-in-place tops are all often encountered in a campus environment, and while some may be in better condition than others, many are in need of some level of repair. 

Ultimately, some level of rehabilitation to account for degradation over time is inevitable, but it can be accelerated by varying factors depending on locale. In the Midwest, climate and weather conditions play a significant role. Tunnel tops are often very close to the surface, and in many instances double as a sidewalk or bearing surface. With little or no cover, the tunnel structure can be adversely affected by heavy use of salt to mitigate ice and snow in the winter. Over time, this salt will seep into cracks or voids and begin to corrode the steel reinforcement within, causing the concrete structure to delaminate or otherwise deteriorate faster than it might in other regions of the country. A compromised structure will exacerbate water infiltration and create risks to the utility services within them, as well as the roads, walkways, and infrastructure above them. In some cases, remediation can involve removing the top and rebuilding in place. In other instances, remediation isn’t as straightforward. 

Regular tunnel inspections are vital for identifying potential damage and tracking degradation, but underground utility tunnels are often classified as confined spaces and require special safety precautions to ensure the safety of the inspection crew. Beyond the applicable personal protective equipment (PPE), air monitoring, heat monitoring, and emergency egress plans should be carefully considered and strictly followed at all times. 

During a typical inspection, visual evaluations, along with concrete soundings, are performed to gauge tunnel conditions. Signs of cracked or delaminated concrete, exposed rebar, or water infiltration are documented and tracked during future inspections for signs of worsening conditions. For brick tunnels in particular, inspection is predominantly visual, identifying mortar loss, brick displacement, bowed walls, and open joints. 

The inspection can also move beyond just the tunnel structure, to include the utility piping within     . Water infiltration can quickly damage piping, insulation, and pipe support systems so sump pumps and drainage systems are checked for proper operation. Pipe supports and expansion joints are thoroughly reviewed for heavy corrosion that may prohibit movement needed to compensate for thermal expansion as operating conditions change within the piping systems. 

Strategies for Longevity

Various maintenance and rehabilitation strategies can be adopted to help sustain and optimize utility tunnels for extended service life. One key consideration is preventing moisture and standing water from infiltrating the tunnels as such conditions can lead to the deterioration of piping systems, pipe supports, and the overall structural integrity of the tunnel. A proactive approach involves designing new tunnels at greater depths, providing separation between the tunnel top and the surface to allow waterproofing systems to be installed not only on the sides, but wrapped around the top as well.

Of course, this is impossible for a tunnel that has been in the ground for decades, so other considerations will be needed to address any issues found during routine inspections. Since water can be very damaging to a utility tunnel system, adding provisions for drainage at low points, fixing broken sump pumps, and sealing infiltration points all become crucial steps in ongoing tunnel maintenance. When minor cracks in concrete tunnel structures are found and water has begun to seep in, epoxy injections can be used to stabilize the situation and keep the cracks from worsening. Where minor delamination or spalling is found, repairs can be made per American Concrete Institute (ACI) and International Concrete Restoration Institute (ICRI) standards. Generally, these repairs involve isolating any damaged concrete from sound concrete, removing the damaged sections, and patching per carefully detailed procedures. Where to perform these types of repairs should be carefully determined with the help of a qualified, full-service engineering team, and in areas of extensive damage, a full roof replacement may be more practical.

Rehabilitation 

RMF Engineering is currently working with two large midwestern universities on repairs to their tunnel systems, helping the universities to identify and prioritize deferred maintenance through ongoing assessments and repair projects. RMF is currently leading a rehabilitation project in which the team has rebuilt around 1,000 feet of one university’s tunnel system. 

Large Midwestern University No. 1

During 2021 and 2022, RMF performed inspections of all utility and pedestrian tunnels at a large midwestern university. These inspections not only documented existing conditions but also provided a roadmap of recommended repairs with associated construction budgets to occur over the next 10 years. The team’s plan identified areas where repairs were not immediately necessary and could be deferred to the future, as well as those that would be in need of more urgent attention. 

Completed in summer of 2023, RMF performed design and construction administration for rehabilitation efforts of two tunnel sections that were identified during the inspection as needing repairs. The team oversaw the removal of a 1960s era tunnel constructed with brick walls and a cast-in-place concrete top. The tunnel was in need of structural repairs, however the only active utilities remaining were telecom cables as the adjacent buildings had been recently renovated and no longer relied on the steam feed from this particular tunnel section. Several options were considered; ultimately, since it was a branch tunnel and not a main trunk of the tunnel system, it was found to be more cost-effective to demolish the tunnel and move the cabling to a new duct bank. Adding a manhole for maintenance access allowed personnel to continue servicing fiber optic switches that were previously accessed through the tunnel. 

The second tunnel section identified was located in the north academic area of the campus and housed a critical stretch of steam distribution piping. Since this was a main tunnel section, with a major steam line feeding a large portion of campus, rehabilitation was deemed an appropriate action. RMF facilitated the rehabilitation with a new concrete top and repairs to damaged pipe support structures. Rebuilding the section also allowed an opportunity to improve egress through the tunnel, remove abandoned piping, and replace damaged light fixtures. Work for both projects was phased to occur during the summer semester while keeping adjacent roadways open to traffic. 

Additional tunnel rehabilitation at the university is in design, with a goal to address the prioritized utility tunnel repairs throughout the main campus over the next few summer semesters. Utility tunnels that are no longer needed will be removed, and the remaining tunnels still in use will be repaired. In tandem with the tunnel structure repair, many of the thermal utilities within will also be replaced or upgraded to ensure reliable operation. 

Large Midwestern University No. 2

At a second large midwestern university, RMF led the rehabilitation of two stretches of a main utility tunnel in an older section of the university’s main campus. 

The university took a critical look at vast stretches of its underground system several years ago to develop a plan for upgrades; its tunnel network stretches more than five linear miles beneath the campus and houses critical utilities including steam, chilled water, domestic hot water, communications, and power lines. Some of its oldest tunnels dated back 100 years, and certain stretches were in need of repairs to prolong their useful life. 

RMF-designed repairs included replacing the roof and some deteriorated wall sections while also replacing most of the thermal utilities within the tunnel. Prolonged water infiltration had corroded utility lines and damaged several pipe supports, including main line structural anchors in the steam distribution piping. A thermal stress analysis model was completed to ensure proper expansion compensation was included in the new steam and condensate piping support system design. New cable trays and racking systems were installed to organize various cables, and obsolete communication cables were identified and removed. Careful planning was required to keep heating and cooling systems active in adjacent buildings, and to stage the main construction between Spring commencement activities and Fall semester student move-in to minimize impacts to campus.

Conclusion

Tunnels are critical to optimizing the lifespan of the many utilities within them. While accounting for tunnel longevity prior to construction is the best approach, there are futures for decades-old tunnels if inspected regularly, properly maintained, and repaired and rehabilitated with care to ensure they remain structurally sound and safe for decades to come.