PROJECT MANAGERS, DESIGNERS, CONTRACTORS AND OPERATORS ALL AGREE UPON THE NEED FOR WELL-PLANNED MONITORING, ADAPTED TO EACH INDIVIDUAL TUNNEL.
Monitoring plays an important role in every stage of the construction of a tunnel:
- At the design stage involving an exploration tunnel for site evaluation or the doubling of an existing tunnel.
- During construction, to accurately evaluate the impact of geological conditions, the effect of the tunnel on nearby structures and construction methods to be used. Design hypotheses can be confirmed, the needs of the support structures defined and the optimum moment for instrument installation in accordance with convergence-confi nement (NATM) methods can be determined.
- Once the tunnel is in service, to enable long-term monitoring thus ensuring the safety of the tunnel over its life span.
Instrumentation is used to accurately quantify certain parameters of structural behavior and to monitor their rate of change. It is possible to observe movement stabilization, or, in the case of acceleration, to deduce the possibility of failure. The comparison of measured values with design values enables the monitoring of tunnel stability and the possibility of implementing corrective measures at the appropriate moment.
Certain projects, such as tunnels in soft grounds, carried out in urban areas, would be practically impossible to achieve without instrumentation and automated data acquisition systems. Roctest Telemac instruments used in major projects in more than 75 countries continue to provide reliable data for critical parameters such as pressure, deformation, displacement, inclination and load.
Selection Criteria for Instrumentation Three major criteria should guide instrument selection:
- Reliability of the measurements obtained (accuracy, resolution, precision and drift)
- Longevity of the instruments supported by numerous references
- Ease of automation, essential for effi cient data collection and interpretation
Roctest Telemac tunnel monitoring instruments respond precisely to these three criteria.
Types of Measurement
The types of measurement and instrument location must be adapted to the existing geological and environmental conditions as well as construction methods. Nonetheless, there are certain general guidelines to follow for instrumentation selection, based on tunnel construction.
Cut and Fill Tunnel
Shallow Tunnel in Unconsolidated Ground
Deep Tunnel in Rock Objectives
- Ensure the stability of the excavations
- Monitor the integrity of the tunnel lining
- Deformation of the rock mass around the excavation
- Stress in the lining