Control Ground Settlement and Sink Hole Risks During Tunnelling and Microtunnelling
When tunnelling through variable ground conditions using microtunnelling or larger tunnel boring machines (TBMs), successful completion can be significantly impacted by surface heave, excessive ground surface settlement and large ground losses. This can result in missed schedule milestones, large consequential costs, safety risks to the public and construction crews, and litigation. Often, the loss of ground control is directly related to management of tunnelling machine operating parameters.
Key to managing these risks is specifying minimum criteria related to TBM operating fluids and operating pressures with follow-up during construction. Face pressure control of EPB or slurry tunnel boring machines must be targeted to avoid surface heave, large ground losses, maximize productivity and comply with ever more stringent surface settlement or volume loss criteria. Well-planned operating targets can, using clear engineering principles, help avoid settlement and sinkhole challenges, and their consequential costs and delays.
Selecting or checking operating pressures can be highly subjective and can sometimes lead to disastrous consequences. While thoughtful machine selection can result in the right tool for the right job, having the right tool does not in itself assure success. Clear guidance for tunnelling control and government agency review and inspection was published in Hong Kong Geo Report 249, but it is not universally applied and is not well known in North America. You and your colleagues are invited to learn from one of the authors, Storer Boone, Ph.D., P.E., Principal and Geotechnical Group Leader, how to proactively mitigate potential losses on your small or large diameter machine tunnelled project.
- Importance of pressure support mechanisms
- Methods for setting target face pressures
- Pre-construction planning
- Quality control
- Importance of ground conditions analysis and comprehensive instrumentation program
- Specification guidelines