CHAPTER 4

Case Examples

Within the survey sent to all DOTs, one question asked if the DOT would be willing to participate in an interview for more detailed discussion of the leakage within their tunnels. Interviews were conducted with the following four DOTs: Arizona, Colorado, Pennsylvania, and Washington State. Table 4 summarizes the case example interviews.

Arizona Department of Transportation

The Arizona Department of Transportation (ADOT) has seven active tunnels operated and maintained by the state. No tunnels are owned by other agencies in Arizona. The seven tunnels include one deck-over structure, the I-10 Deck Park Tunnel, which supports a city-owned park.

Constructed in 1990, the approximately 2,600-ft-long I-10 Deck Park Tunnel is the longest tunnel in Arizona’s inventory and is a rectangular box structure in soil. The other Arizona tunnels are horseshoe structures in rock.

ADOT has experience with leakage in some of their tunnels, although leakage is reported to be minor. Two of the horseshoe tunnels are unlined rock tunnels and experience minor groundwater infiltration. These tunnels are in the mountains and carry low average-daily-traffic roads. The tunnels experience more inflow of groundwater during the winter and monsoon seasons.

The I-10 Deck Park Tunnel consists of a series of 19 units, each 150-ft-wide, post-tensioned box girders, with a waterproofing membrane on top and then covered in fill. Between each unit is a 1.5-in. expansion joint, which may have a backer rod and sealant, covered by the waterproofing membrane above. This structure carries the Margaret T. Hance Park owned by the City of Phoenix. The park houses a Japanese garden and pond on top of the structure. It also supports Central Avenue Bridge and a few buildings above. The deck-over structure experiences water dripping through the joints between bridge units. The park is mostly a large a grass area, and irrigation is the main source of the water leaking through the joints.

ADOT noted that some leakage occurs near the portal onto traffic below and is a source of complaints from the public. In addition, ADOT noted leakage into the tunnel support spaces through cracking. The support spaces are constructed as a shed-type structure attached to the tunnel on the backside of the abutment. Where possible, ADOT staff exposed and installed new waterproofing to reduce leakage. This mitigation has been successful in the areas where ADOT staff have been able to implement it, but finding a tear in the membrane is difficult. Additionally, scaling is evident along the interior abutment walls in the access areas behind the portals because of the leakage at the ends of the box units.

To date, ADOT has not used non-destructive testing (NDT) to identify leaks because the leaks have been readily detectable by visual methods. ADOT staff would like to use NDT in the future

Table 4. Summary of case example interviews.

to investigate the post-tensioning strands of the deck-over structure to see if water infiltration may be causing any deterioration. Dye testing was also mentioned as a potential means to identify leaks from the pond above, but that has not been used so far.

Grouting from within has not been used as a potential remediation for leaks because of the 6-ft depth and the post-tensioning that exists in the deck at the I-10 Deck Park Tunnel. For the deck-over structure, repair or investigation has been only in conjunction with park maintenance activities. During construction in the park area, the DOT removed fill down to the waterproofing membrane to inspect for defects and provide repair as needed. This approach, to find the source and fix it from the outside, is ADOT’s preferred approach to solving the leaks in the deck-over structure.

ADOT has a dedicated tunnel maintenance group—the Transportation Systems Management and Operations (TSMO) division. TSMO staff perform basic maintenance for the tunnels, but TSMO contracts out major repairs or rehabilitation work because sufficient staff are not available. Consultants perform routine inspections of ADOT tunnels. The maintenance group is not typically involved in reviewing new designs or in developing maintenance agreements on air rights projects.

Acceptance criteria for leak remediation projects were briefly discussed. Currently, ADOT has no criteria for accepting a certain volume of leakage upon completion of new tunnel construction or leak remediation projects.

Colorado Department of Transportation

The Colorado Department of Transportation (CDOT) owns and maintains 20 tunnels. In addition, CDOT has two deck-type structures constructed as snowsheds, providing a path for avalanches. The two deck structures will be added to the CDOT inventory next year, bringing the total number of state-owned tunnels to 22. In addition, the federal government and local or private entities within the state own a total of 19 other tunnels.

Complex tunnels have dedicated tunnel maintenance crews to cover daily operations and maintenance. For non-complex tunnels, typically three separate maintenance crews provide maintenance: roadway maintenance, traffic services for electrical, and information technology support services for electronics. Major leak remediation is handled by external contractors.

CDOT indicated the source of water infiltration in mountain and canyon tunnels is from groundwater and surface runoff. CDOT staff noted that greater leakage occurs in shotcrete tunnel liners than in those with a cast-in-place (CIP) concrete liner for certain tunnels.

CDOT staff noted greater leakage is observed in the springtime for the Eisenhower-Johnson Memorial Tunnel; at the Wolf Creek Pass Tunnel, water has been flowing through the liner. Most leaks in CDOT tunnels are seasonal and at cold construction joints in the concrete liner, and the leakage causes deterioration to the joint. The seasonal leakage is most problematic when Winter changes to Spring and groundwater starts flowing but temperatures are still below freezing. The Eisenhower-Johnson Memorial Tunnel has had heaving of pavement from these freeze-thaw issues caused by groundwater saturation.

CDOT has implemented chemical grout repairs at joints (using a contractor) and installed additional drainage systems to direct water from the roadway. Prior repairs have included applying pneumatic concrete over the leaking areas of the liner and adding a drainage mat under the shotcrete to direct the water from the roadway. Because the leaks are seasonal, they are often not active and thus not fully documented on NTIS tunnel inspections. CDOT is implementing a grouting program that will start at the Eisenhower-Johnson Memorial Tunnel to mitigate groundwater infiltration.

CDOT has issues with support space leakage within the tunnel in the Eisenhower-Johnson Memorial Tunnel, mainly around the interface with the mountain, and experiences leaking roof issues from ice and snow at the buildings at either end of the tunnel.

CDOT staff acknowledged it is difficult to determine the best means to identify the cause of and develop solutions to water infiltration. The Wolf Creek Pass Tunnel, after 17 years of relatively dry operation, is leaking—water springs from the liner for a short period at the end of winter. CDOT staff noted that if it were from a clogged underdrain system, they would like to know the best practices for investigation. Above the Eisenhower-Johnson Memorial Tunnel, the original landslide construction installed an underdrain system and the drains feed to a culvert that vents to a nearby creek.

CDOT participated in the SHARP2 study for NDT to identify leaks within the tunnel. Both thermal imagery and LiDAR scans were used during the study with seemingly good results, and CDOT endorsed the use of these technologies. The results were never compared to actual field inspection data to verify the locations of water leaks. CDOT staff have implemented scans at six tunnels to date, including tile-lined CIP and shotcrete liners. The thermography shows that water has been accumulating at the edges where the drains exist. Water is at a different temperature than the subgrade, so it shows up, and the thermal camera used is sophisticated enough to detect small temperature differences. CDOT staff tried using thermography near the portals but found the technique less useful there because of warming from the sun and outside temperatures. CDOT staff also analyzed using thermal couplers to determine optimal thermal signature by the

time of day and with or without ventilation. Ventilation did not influence or improve the results. CDOT staff noted they liked thermography better for identifying moisture and changes in temperature in shotcrete liners. Although the results were interesting, CDOT staff cautioned that the thermal cameras were extremely expensive ($20K for rental in 2018). The equipment was very effective at documenting liner leakage using temperature, but leaks are easily confirmed visually using traditional inspection.

Pennsylvania Department of Transportation

PennDOT owns and maintains 9 tunnels, while county, municipal, and state toll agencies own an additional 23 tunnels in the state. Within Pennsylvania, most of the state-owned tunnels are in the Pittsburgh area. Four of these nine tunnels are horseshoe and were constructed in rock or mixed-face conditions. The remaining tunnels are rectangular and in varying soil and mixed conditions. The longest tunnel is approximately 5,900 feet long.

A few of PennDOT’s tunnels have minor leaks, typically at joints and at transitions to cut- and-cover construction at the tunnel ends. The leaks are not of major concern because they are not creating a hazard or structural deterioration currently. The worst leakage occurs in the Squirrel Hill Tunnel, where ice builds up along one particular joint. Other tunnels with minor leakage include the Corliss (owned by the City of Pittsburgh) and Armstrong tunnels. The water is typically worst in the first or second joint in from the portal (which may correlate with a transition in structure). Keeping water off functional systems and removing icicles are the priorities.

PennDOT also reported water infiltration issues into support spaces; however, those occur in the portion of the tunnel not underground. The issue is related to portal building roof leakage rather than tunnel leakage. This is one of PennDOT’s major leakage issues.

PennDOT has dedicated tunnel maintenance staff who perform routine cleaning and maintenance activities and are responsible for removing icicles formed because of water infiltration during the winter months. The maintenance staff does not perform leak remediation or other rehabilitation work. Instead, staff initiate a rehabilitation project when structural deterioration has occurred.

Rehabilitation was previously completed on three of their tunnels in Pittsburgh. PennDOT removed the ceiling in the Squirrel Hill and Fort Pitt tunnels, and water was not a significant issue. PennDOT had not seen evidence of water infiltration above the ceiling before it was removed. The neighborhoods constructed above those tunnels are dense and the resulting ground above the tunnel is somewhat impervious, reducing the amount of infiltration into the ground surrounding the tunnels.

The PA Turnpike Commission (PTC) owns and operates 10 tunnels throughout the state. PennDOT reported that PTC tunnels have been reported to leak primarily at the joints in the concrete liner. Two of the PTC’s tunnels that form the eastbound and westbound tubes of the Tuscarora Tunnel are undergoing major rehabilitation. The eastbound tube will have a full umbrella PVC waterproofing membrane installed inside the existing concrete liner and a new shotcrete liner placed as the final inside surface. Water infiltration will be captured by the waterproofing membrane and will be directed to the tunnel drainage system. The westbound tube is undergoing a less extreme rehabilitation with new vertical drains being placed in the wall at each liner joint to redirect water infiltration.

PennDOT identified two deck-over structures within the state, both owned by other agencies. One structure at the Allegheny County Airport consists of an adjacent box-girder bridge with composite deck and a waterproofing membrane under fill. The other, in Pittsburgh, also consists of an adjacent box-girder bridge with a concrete deck, waterproofing membrane, a concrete

protection slab, and fill, but carries a park on top. PennDOT provided oversight during the design and construction of this project due to federal funding; however, the City of Pittsburgh took ownership after construction and is responsible for future maintenance. Because the project is relatively new, there have been no issues with leakage. Both structures are being reported to FHWA as tunnels.

PennDOT staff participated in the SHRP2 project using NDT for tunnel liners, but their participation did not involve using technologies specifically for leakage. Because PennDOT has only minor leakage present throughout their state-owned tunnels, PennDOT staff rely on visual detection to locate leaks. When asked what they would like to learn through this study, PennDOT staff indicated they (1) would appreciate seeing repair schemes and what other states are doing, (2) would like to learn more about how to repair the damage and mitigate water infiltration in their tunnels, and (3) would like to learn about products that other DOTs have had success with. PennDOT staff observed that construction of deck structures, with their unique structural configurations such as post-tensioned box beams with facilities installed above, present new challenges in identifying and solving water infiltration.

Washington State Department of Transportation

WSDOT owns and operates 55 tunnels with more under construction at the time of the interview. Four tunnels within Washington State—three rail tunnels in Spokane and one tunnel under a parking garage in the City of Olympia—are owned and operated by another agency. Six tunnels are owned by the National Park Service. Deck-over structures (or lids as WSDOT refers to them) are common within Washington State—over 11 of them are present throughout the state. Most of the deck-overs in Washington State have a park and hardscaping with limited usage lanes with more of a “city street” feel instead of a bridge. One significant structure is a convention center structure spanning the I-5 interstate.

The tunnels owned by WSDOT vary in length, with the Alaskan Way Tunnel being the longest at 12,244 feet. Three of the tunnels are horseshoe structures constructed in soil, fifteen are rectangular and constructed in soil or mixed conditions, and the remaining tunnels are circular bored tunnels in soil.

Approximately 14 of WSDOT’s tunnels have active water infiltration, but many of the others show signs of past infiltration with areas of water staining. Typically, the cut-and-cover tunnels have a good waterproofing layer which is reasonably watertight on top, but leakage occurs through the walls. Water infiltration is most prevalent in the support spaces (e.g., plenums and utility rooms).

A concern that arises from water infiltration in WSDOT’s tunnels is the formation of icicles. In some mountain tunnels it is not a major concern because the roadway is already being treated for ice and some mountain roads are even closed during the winter months. The bigger concern is when water infiltrates support spaces or egress areas and freezes, creating a potential slipping hazard. WSDOT staff have noted leaching into utility spaces and plenums which leaves a residue on the floors. WSDOT also reported issues with mineral deposits in the drainage system of one tunnel (mitigated by using a snake through the drains to clear them).

WSDOT has dedicated tunnel crews for routine tunnel maintenance but uses the state’s bridge maintenance crews to assist with complex repairs or rehabilitation (including epoxy injection). WSDOT performs its own leak mitigation with in-house personnel, who are also experienced with large pontoon bridge structures that have zero tolerance for water intrusion. WSDOT staff indicated they have had success with the following products for leak mitigation: (1) DE NEEF Denepox I-40 for epoxy injection of tunnel liners, (2) DE NEEF Cut Pure for injection

of leaking grout ports, and (3) XYPEX Concentrate (crystalline coating/sealer) for sealing small surface cracks. Contractors are used as needed for tunnel repairs based on the complexity of the work and the availability of in-house crews.

WSDOT is the only agency that reported having documented acceptance criteria for water infiltration as part of a new tunnel commissioning. The criteria, developed for the State Route 99 tunnel, required the contractor to waterproof the tunnel for the life of the structure with an allowance for 1 gallon of infiltration per minute per 1,000 feet length of tunnel. The criteria also included the following stipulations:

• No more than 1 drip per minute in any location.
• No drips allowed over the roadway.
• No water infiltration allowed where it could cause damage to or malfunction of electrical equipment.
• No infiltration of soil particles permitted.
• Embedded electrical boards, conduits, and other similar elements must be waterproof and watertight.
• Interface between cut-and-cover and bored construction must be watertight.

WSDOT staff noted the criteria proved to be difficult to (1) measure in the field and (2) enforce when it came to having the contractor mitigate any leaks beyond the allowable criteria.