Practices for Controlling Tunnel Leaks (2024)

APPENDIX C

Draft Interview Questions

Introductory Information

• What is your position and how long have you been with the DOT? How long have you been associated with tunnels (and bridges)?
• How many tunnels does your DOT own? Do you maintain and operate all of these tunnels?
• How many tunnels in the state are owned by other agencies?
• Are there any deck-over type structures (air rights structures) in your state that are longer than 300 ft (that could be considered a tunnel)? If yes, what is built on top of the deck?
• Is your asset management/maintenance group involved in developing the maintenance agreements for the deckover structure?
• Is your asset management/maintenance group involved in the reviews of the deckover structure for review of waterproofing design?

Asset Management

• Do you self-maintain all of your tunnels? Do you make the repairs such as leak remediation?
• Do you perform leak remediation as a maintenance task or is the work contracted to a specialty contractor?
• How are your tunnel needs prioritized (funding) compared with other DOT assets?
• Do you have issues with air rights owners that are responsible for maintaining the top surface of a tunnel structure and the DOT is only responsible for the underside?

Prevalence of the water infiltration problem and degree of severity

• How many of your DOT tunnels leak?
• Do you also have problems with support space leakage that impacts tunnel equipment? If yes, is the support space located underground? Built adjacent to the roadway?
• Characterize the leakage- how great is the water (drips per minute)? Is it seasonal? Or heavier following heavy rains?
• What problems does the leakage cause for your DOT- structural deterioration, icicles, slippery roads, damage to functional systems, etc.?
• Do you have issues with mineral deposits from the infiltration? What problems does it cause-i.e. clogging drainage systems? What do you do for maintenance or rehab in that case? Frequency of flushing? Is it effective?

Sources of Water Infiltration

• When you find a leak, how do you investigate it? Does it begin with a review of the construction drawings?
• Has your DOT used Non-Destructive Evaluation methods to investigate or locate leaks?
• What types of NDE have been used and were any of them effective?
• What are your primary sources of water infiltration (Groundwater, Rain runoff, Utilities, Other)?
• How did you determine the source of infiltration? Has been there any testing to confirm or rule out sources of water infiltration? What other agencies have you had to coordinate with to determine the source of leakage – i.e. water department, sewer department, other?

Relationship between tunnel construction type and leaks

• Which tunnel leaks the most for your state DOT? What is the construction type (cut and cover, bored, mined, submerged, unlined rock, etc.)? How many lanes does it carry? Would you consider it to be heavily travelled (ADT)?
• Where is the leakage greatest- at expansion joints, cracks, penetrations, voids behind liner, other?
• Are there any embedded utilities in the tunnel structure that contribute to leakage?
• Are there other tunnels that leak? Any significant differences from the first tunnel or is there anything unique about the structure type, the areas of infiltration, the problems it causes?

Mitigation Methods

• What is your general mitigation strategy?
• What method of remediation has been most effective for your DOT’s tunnels?
• If grout injection is typically used, would you be willing to share the types of grout used?
• How effective has injection grouting been? Do you know the history regarding previous grouting and whether it was effective and for how long?
• Are there any other really successful repairs that you have made that solved your leakage problems?
• Have there been unintended consequences of mitigation methods? How long after the initial repair did you notice the unintended consequence?
• How did you address the unintended consequence? Was it addressed at the same time as the original repair, or in a followup contract or maintenance?

Acceptance Criteria

• Does your agency have specific acceptance criteria incorporated into the design of a new air rights deck structure or a tunnel? How does your agency ensure a watertight structure during design?
• Are there specific thresholds for acceptance of work on a remediation contract? Is there a period of dryness that needs to occur following rehabilitation (i.e. 1 year, 5 years, 10 years)?

Other

• What would you like to get out of this study?
• What would you most like to learn or better understand through this study?