The Characterization of Delamination Processes with Respect to Waterjet Shotcrete Removal During Tunnel Liner Repair and Maintenance

The repair of concrete and shotcrete liners that have been structurally compromised or damaged is a common activity associated with the maintenance and rehabilitation of tunnels and other types of underground workings. Age, in-situ stresses, geology, chemical and physical decomposition, accidental impacts, and water flow/seepage are but just a few of the many factors that necessitate the repair of these structural systems over time. In many cases, it is prudent to limit the repair to the isolated removal of the structural liner around the damaged area rather than the complete excavation of large sections of the support system. In these applications, traditional methods of liner removal include the use of hydraulic or pneumatic hammers that break and excavate the liner material through repetitive percussive impacts. In operating environments where working heights are less than 20 m, these hammers are usually mounted to articulated booms attached to mobile rubber-tired or track equipment, such as a mechanical scaler. In applications that extend beyond the reach of conventional scalers, the height of the operating envelope usually necessitates the use of man-lifts, where workers manually remove the damaged areas from these elevated platforms using hand-held equipment. In both applications, there are significant drawbacks to the use of these traditional methods. It is a long-held belief that the percussive impacts generated by hydraulic/pneumatic hammers while removing the compromised area of the liner also causes unintentional damage to the surrounding intact shotcrete and/or concrete because of the propagation of fractures and the delamination of the liner from the rock substrate, as well as any contained rebar or wire mesh/screen backing. In addition, there is a host of potential safety hazards commonly associated with the use of these traditional technologies. This is particularly true for work performed off of elevated platforms, including the workers close proximity to unstable roof/back, the potential of falling from these platforms, the man-lift tipping or overturning, and the limited ability for rapid egress. To circumvent these technical and operating challenges, this research seeks to develop a unique system that utilizes waterjet technology as the primary excavation tool. Building upon the success of previous CSM research activities in underground rock scaling and scarification, empiric evidence indicates that waterjets are capable of selectively removing damaged areas of support liners without structurally compromising or harming intact material around the area being repaired. The primary research objective is to compare and contrast the unintended damage caused to the surrounding structural liner and rock substrate by both mechanical impact hammers and waterjet excavation methods during empiric testing. This analysis will involve physical testing on instrumented shotcrete panels designed to quantify fracture propagation, substrate delamination, and stress distribution. The intent of this research is to facilitate a better understanding of the dynamic excavation processes associated with liner repair in hopes of developing a future prototype system applicable for field testing.


  • English


  • Status: Active
  • Funding: $193098
  • Contract Numbers:


  • Sponsor Organizations:

    Ramax LLC

    Orlando, FL  United States 

    Hugh Miller

    Golden, co  United States  80401

    University Transportation Center for Underground Transportation Infrastructure

    Colorado School of Mines
    Golden, CO  United States  80401

    Office of the Assistant Secretary for Research and Technology

    University Transportation Centers Program
    Department of Transportation
    Washington, DC  United States  20590
  • Managing Organizations:

    Colorado School of Mines, Golden

    1500 Illinois Street
    Golden, CO  United States  80401
  • Project Managers:

    Miller , Hugh

  • Performing Organizations:

    Colorado School of Mines, Golden

    1500 Illinois Street
    Golden, CO  United States  80401
  • Principal Investigators:

    Miller , Hugh

  • Start Date: 20170515
  • Expected Completion Date: 20190615
  • Actual Completion Date: 0
  • USDOT Program: University Transportation Centers

Subject/Index Terms

Filing Info

  • Accession Number: 01660192
  • Record Type: Research project
  • Source Agency: University Transportation Center for Underground Transportation Infrastructure
  • Contract Numbers: 69A3551747118
  • Files: UTC, RIP
  • Created Date: Feb 16 2018 7:46PM