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Tunnel Induced Deformation using Modern Tunneling Equipment

Description:

A significant risk in urban transportation tunneling is building, utility and other structural damage caused by tunneling-induced deformation. Considerable effort, time and cost is expended to account for and to mitigate the effects of tunneling-induced deformation. Conservative values of volume loss, e.g., 0.5 to 1.0%, are used in preliminary building assessment to identify structures requiring fortification or protection. Numerous buildings are either strengthened or ground improvement efforts are taken to protect them, e.g., compensation grouting. Both efforts are costly and time-consuming. If such efforts were not required, tunneling cost and risk could decrease significantly.

Tunneling practice in North America and worldwide over the past decade has shown that tunneling-induced ground deformation has decreased significantly. This is largely the result of pressurized face tunnel boring machine (TBM) tunneling and their proper operation. Volume loss on the order of 0 – 0.3% are increasingly common. The tunneling industry therefore operates in an environment where large volume losses (0.5-1.0%) are often planned for yet much lower values are realized (0-0.3%). The goal of ‘negligible-deformation’ TBM tunneling is arguably within reach. To realize this goal, the community needs to better understand TBM tunneling-induced deformation control. It is well understood that inadequate face pressure, the shield annulus and the tail shield/segment gap are the general contributors to ground and building deformation. However, there are many important questions about these. Further, changes in geology and hydrogeology often are the cause of deformation. Improved understanding of how TBM pressures can mitigate these effects is needed.

Objective:
  1. Document and analyze, for a variety of North American tunneling projects completed over the past 10-15 years, observed ground and building deformation as a function of face, shield annulus and grout pressures, as well as geology and geometry (diameter, depth, etc.).

  2. Develop and document the cause and effect relationship between these TBM-induced pressures and the observed deformations. Convey deformation levels (as a function of TBM-induced pressures and in different geology) in a probabilistic fashion. Use computational modeling with GDR information and TBM parameters to support this analysis.

  3. Develop risk-based criteria for TBM operation (required pressures) that control deformation (but that also does not slow production).

Benefits:

Better control of TBM tunneling-induced deformation.

Less building fortification, less ground improvement = lower cost.

Related Research:

A detailed literature search will be conducted in order to obtain available information in regard to addressing this specific problem. Literature searches will include national technical reports, state DOT libraries and personnel queries, university research programs, and association work.

Sponsoring Committee:AFF60, Tunnels and Underground Structures
Research Period:24 - 36 months
Research Priority:High
RNS Developer:Mike Mooney
Source Info:Committee members and friends
Date Posted:12/30/2017
Date Modified:01/05/2018
Index Terms:Tunnel borers, Tunneling, Tunnels, Deformation,
Cosponsoring Committees: 
Subjects    
Highways
Construction
Geotechnology
Bridges and other structures
Vehicles and Equipment

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