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.
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csengineermag.com
Summer 2024
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