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The Hanging Lake Tunnel crack repair was a major 2007 reconstruction of a damaged ceiling slab in the transition tunnel above Interstate 70’s eastbound lanes in Glenwood Canyon, Colorado. CDOT closed the tunnel on March 30 after the crack had widened, deepened and begun leaking; it reopened on October 3, while backfill and seeding work continued. The repair combined temporary structural shoring, excavation, crack grouting, extensive reinforcing steel, a new concrete slab above the existing slab and reinforced shotcrete below it. The project account also makes clear why the work took months: crews had to reach the slab through constrained rail and trail access, remove and stockpile enormous quantities of rock and soil, and carry out the repair in limited space.
This is a historical case study, not a current repair specification. The figures and timeline below come from Building Design + Construction’s August 11, 2010 project account. That account reports the project as it was completed in 2007; it is not a later engineering review or a long-term monitoring report.
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The damaged structure was a 105-by-49-foot ceiling slab in a transition tunnel over the eastbound lanes of the Hanging Lake Tunnels. The account describes the tunnels as 4,000 feet long and the Interstate 70 route through Glenwood Canyon as 12.5 miles. The Federal Highway Administration found a crack during a routine inspection in July 2006. It was initially reported as 70 feet long. By the time CDOT closed the tunnel in March 2007, it had extended to 80 feet, widened to 1.5 inches, reached 4.5 feet deep and begun leaking.
Joe Elsen, P.E., then a CDOT Region 3 program engineer, gave approximately 500 cubic yards of rockfall onto the slab in 2002 as the probable cause. That is an attributed explanation in the project account, not an independently established finding. The distinction matters: the report describes a plausible history for the damage, but does not provide a forensic investigation, structural calculations or a separate assessment confirming the cause.
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A long, widening, deepening crack that is also leaking was not treated in the report as a surface-sealing job. The repair addressed the damaged slab as a structural element, while also requiring access to its upper side, temporary support and work below it. The source does not publish the design calculations or explain why this particular assembly was selected over alternatives, so the project should be understood as a documented solution for this site—not a standard detail that can be copied to another tunnel.
Why did the tunnel close, and when did it reopen?
CDOT closed the tunnel on March 30, 2007, after the crack had worsened and begun leaking. It reopened on October 3. The project account says backfill and seeding continued after reopening, so the date marks the tunnel’s return to traffic, not the end of every restoration task.
The report estimated that 20,000 vehicles a day were shifted to the detour. That figure is the account’s estimate, not a current traffic count. It helps explain the schedule pressure: the repair was a structural project in a difficult location, but it also took place on a route where a closure affected substantial daily traffic. The article says a $132,000 early-completion incentive applied to related highway rehabilitation work. It does not identify that amount as a payment for the tunnel repair itself.
What did the repair involve?
The reported repair used several linked stages rather than a single patch. First, crews monitored the slab and supported it; then they exposed and repaired the damaged area and added reinforced concrete elements on both sides of the existing slab. In the project account, Pete Mertes, P.E., CDOT resident engineer, described the design as “a concrete sandwich.” That phrase refers to the new 12-inch reinforced concrete slab above the existing slab and a 6-inch reinforced shotcrete slab below it. It does not, by itself, describe the design calculations or establish how the assembly has performed since construction.
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- Install monitoring and temporary support. Crews installed three strain gauges and erected structural steel shoring beneath the slab. The account reports 210,000 pounds of shoring steel arranged in 12 bents, set 8 feet on center. The shoring supported the work while the damaged slab was exposed and repaired; the source does not publish gauge readings or say how the instrumentation was interpreted.
- Excavate above the slab. Crews removed rock and soil to reach the slab from above. The project account reports that 25 million pounds of rock were removed to reach it. Excavated material had to be handled in the restricted site and some was retained for later backfill.
- Grout the crack and add reinforcement. After exposure, crews grouted the crack. They cored 1,130 holes through the existing 4.5-foot-thick slab for reinforcing steel. The report lists 95,000 pounds of reinforcing steel for the repair. It does not provide bar layouts, grout specifications or details needed to reproduce the work.
- Build the upper reinforced concrete slab. A new 12-inch-thick reinforced concrete slab was placed above the existing slab. The account reports 210 cubic yards of concrete for the top slab and identifies it as CDOT Class D concrete with a Xypex additive.
- Apply the lower shotcrete slab. Crews installed a 6-inch reinforced shotcrete layer beneath the existing slab. The report gives the quantity as 650 square yards and says Xypex additive was used in the shotcrete as well. It does not name a specific additive formulation.
- Address drainage and restore the site. The work also modified drainage and included restoration of tunnel surfaces. Crews used stockpiled excavated material for backfill, with backfill and seeding still continuing after the October 3 reopening.
The order is significant because the access and support work made the structural repair possible: the crew could not simply reach the crack from a convenient work platform and patch it. The account documents the broad sequence, but does not give construction drawings, mix designs, inspection records or the full engineering basis for each step. Those omissions limit what another project team can infer from the case.
Why did the project take so long?
The duration reflected the work needed to reach and safely repair the slab, not just the time needed to place concrete. Access was constrained by the tunnel and the Cinnamon Creek Complex. The slab’s upper side was reached by railroad cars and a steep trail, while the work area itself had little room for equipment and materials. Gary Coffey, Concrete Works site superintendent, summarized the constraint this way: “In this limited space, everything from the equipment to the repair processes has to go single file.”
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The excavation quantities show the scale of that access problem. The account reports 6,500 cubic yards of rock shipped out by rail car and 12,000 cubic yards of rock and soil excavated and stockpiled for later backfill. These are reported project quantities; the article does not reconcile them into a single total, and they should not be treated as interchangeable measures. A large excavator had to be partly disassembled to fit through the railroad tunnels. Material that could not be hauled away immediately had to be stockpiled in a setting where space was already restricted.
Temporary shoring added another layer of logistics. Before crews could progress through excavation, crack grouting and reinforcement, the slab required support from below. Then more than a thousand holes had to be cored through a slab already 4.5 feet thick. Concrete placement and shotcrete work followed only after access, support and reinforcement had been addressed. Each phase depended on the previous one, and equipment, people and materials had to move through the same constrained work zone.
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Dick Brasher, Concrete Works vice president, described the process as an evolving construction problem: “We responded on the fly, and have been working on the repair puzzle piece by piece.” He also said the work required “a collaborative approach between the CDOT and Concrete Works team.” These comments describe the project team’s account of the coordination challenge; they are not a substitute for the technical records that would be needed to assess the design or its long-term outcome.
What do the reported project figures show?
The quantities underline how much of the job was access, excavation and structural reinforcement. All figures in the table are reported in the 2010 project account about work performed in 2007; they have not been independently verified here.
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| Item | Reported figure | What it describes |
|---|---|---|
| Damaged slab | 105 by 49 feet | Slab dimensions given in the project account |
| Rock removed to reach slab | 25 million pounds | Reported excavation quantity |
| Rock shipped out by rail cars | 6,500 cubic yards | Material hauled from the site |
| Rock and soil stockpiled for backfill | 12,000 cubic yards | Material retained for later restoration |
| Shoring | 210,000 pounds; 12 bents at 8-foot spacing | Temporary structural steel support |
| Reinforcing steel | 95,000 pounds | Steel reported for the slab repair |
| Core holes for rebar | 1,130 | Holes through the existing slab |
| New top concrete slab | 12 inches thick; 210 cubic yards | Reinforced concrete above the original slab |
| Bottom shotcrete | 6 inches thick; 650 square yards | Reinforced shotcrete below the original slab |
| Estimated repair cost | $6 million | Estimate reported at the time, not a current price |
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These quantities are useful for understanding the scope, but they are not enough to compare costs or establish a transferable unit price. The account does not provide a cost breakdown, final audited expenditure, inflation adjustment or a clear basis for comparing the repair with another tunnel project. Its $6 million figure is an estimate from the period, not a present-day budget target.
What does the report say about waterproofing?
The project account says Xypex additive was used in the CDOT Class D concrete top slab and in the shotcrete. It does not identify a formulation, dosage, current product version or project-specific test result. Brasher said, “This additive should provide nearly 100-percent waterproofing.” That is an attributed expectation, not independently verified performance data.
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The distinction is especially important because the crack was reported to be leaking, and the project also modified drainage. The account does not provide post-repair leakage measurements, later inspections, crack-movement data or a monitoring period. It therefore supports the statement that the additive was used and that a project participant expected it to help with waterproofing; it does not establish long-term waterproofing performance or suitability for another structure.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What can this case teach other tunnel repair projects?
The strongest lesson is that repair access and structural work cannot be separated. In this project, the slab was reached through rail access and a steep trail, the excavation had to be managed and partly stockpiled, the equipment had to fit through railroad tunnels, and temporary shoring was installed before the repair sequence could proceed. A repair plan that considers only the final concrete section would miss much of the work that shaped the schedule and construction method.
A second lesson is to distinguish reported project facts from engineering conclusions. The project account gives dimensions, quantities, dates and a probable cause attributed to a CDOT engineer. It does not provide the calculations, drawings, alternative analyses, material submittals or later condition reports needed to independently evaluate the design. For a comparison with another tunnel repair, the useful dimensions are the structural approach, access and excavation logistics, traffic management, drainage work, schedule and reported cost—not simply whether both projects used concrete.
Finally, the reopening date is not evidence by itself that the repair remained successful over the long term. The source records that the tunnel reopened on October 3, 2007, while restoration continued. It does not include later monitoring or an independent assessment. A reader can accurately describe what was built and when traffic returned, but cannot use this account alone to claim a particular service life or current condition.
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Frequently Asked Questions
Can the $6 million estimate be used to budget a tunnel repair today?
No. It is a 2007-era estimate reported in a 2010 account, with no cost breakdown or inflation adjustment. A present-day estimate would need a defined scope and site-specific information about access, excavation, traffic control, materials and schedule.
Does the Hanging Lake Tunnel report prove the repair is still performing well?
No. It records the construction approach and reopening, but provides no later inspections, crack-movement measurements or leakage monitoring. The account therefore cannot establish the repair’s current condition or service life.
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What would an engineer need before applying this repair approach elsewhere?
At minimum, the engineer would need the other structure’s condition assessment, loading and design information, site geology, water and drainage conditions, access constraints and construction sequencing requirements. The Hanging Lake account does not provide enough drawings or calculations to serve as a reusable design specification.
