Advanced Ground Prediction System

Work Packages 3/4/5

Several beneficiaries of the NeTTUN consortium participate in a dedicated working group (GT24) within AFTES (the French chapter of the International Tunnel Association). What the NeTTUN beneficiaries have noted is that there is a strong requirement from all GT24 participants for effective ground prediction systems.

Currently the construction of tunnels is heavily reliant on time and cost expensive experts, brought in outside of the awarded contractor’s team, to analyse data provided by existing ground prediction systems. These outputs are insufficient and result in tunnelling projects working in practically continuous “moderate risk” warning scenarios that operators tend to ignore after a number of weeks of apparently safe progress, resulting in relatively frequent geotechnical accidents. Most existing ground prediction methods require stopping the excavation for several hours, which relegate them to a once per week activity and at best performed during planned maintenance operations. Overall this by far exceeds the available nominal idle time corresponding to the construction of a ring in a segmental lined tunnel.

Hence there are strong demands from tunnelling contractors for:

• A fully automated system, displaying a reliable “Go/Slow/Stop” type of information that a TBM operator can easily understand and follow. There is therefore a need for a decision-aid system that can process the prediction system information into a more digestible format. This is our first NeTTUN objective.

• High-speed ground prediction operations that are transparent (in time) to tunnelling. The proposed approach is that the ground prediction operations are performed during ring construction time, resulting in no additional time loss. This is the second NeTTUN objective.

• Systems to identify large obstacles that can obstruct the digging (e.g. other tunnels, cavities, boulders, foundations, archaeological remains, etc) as well as soil changes (e.g. from gravel to fractured rock).