Published Fri 25th Oct 2024
A key element in the Ibbenbüren Mine Dewatering Project in northern Germany is the construction of a 7.4 km tunnel to drain groundwater from the former coal mine. Set for completion in 2025, the project involves unique technical challenges that require precise, real-time monitoring.
VMT, a leader in tunnel monitoring, was hired by contractors Wayss & Freytag and Züblin to oversee the tunnel’s monitoring.
VMT selected Senceive’s advanced wireless sensors to meet the specific demands of this project.
Tackling the Challenge: Pea Gravel and Ring Convergence
One of the unusual features of the Ibbenbüren tunnel project was the use of pea gravel instead of traditional cementitious grout to fill the overbreak between the precast segmental lining and the surrounding ground. The use of pea gravel was specified because if its drainage properties, but it introduced variability in the bedding of the rings, making it critical to monitor for convergence and deformation. Unlike grout applied under pressure, pea gravel binding lacks the same level of consistency, so indirect control over the tunnel rings through precise measurement was essential.
How VMT’s Ring Convergence Measurement System Works
To ensure the stability of the tunnel rings, VMT selected Senceive’s Nano Triaxial Tilt Sensors for a Ring Convergence Measurement System (RCMS). The RCMS operates using these small tilt sensor nodes (inclinometers) mounted on each segment of the rings being monitored. The precise MEMS tilt sensors in the nodes detect any changes in rotation of the segments, which can be used to determine deformation or convergence in the tunnel structure.
The data from the sensor nodes is transmitted through a wireless mesh (FlatMesh™) to a Gateway, which relays the information to a data visualisation system for evaluation. VMT monitoring experts integrate the data seamlessly with other platforms such as TUnIS Navigation Office and MODUS, allowing for easy transfer and further analysis of the data.
RCMS – Ring Convergence Measurement System
Strategic Sensor Placement and Optimisation
In a typical tunnelling project, two or three rings are typically monitored at any time, spaced 20 to 40 metres apart. Once the grout has hardened and the rock has settled, the sensors are removed and mounted on new rings to continue the monitoring process. This methodology ensures continuous and precise assessment of the tunnel’s structural integrity.
For this project, it was determined that a greater density of data was required. The VMT team therefore established 10 measuring cross-sections, spaced 10 metres apart, covering a length of at least 100 metres. This setup allowed for the optimisation of sensor transmission rates, fine-tuning the system for peak efficiency and data accuracy.
Triaxial Tilt Sensors mounted on tunnel rings - used to measure tunnel convergence
Why the Ibbenbüren Project Is Important for VMT
The Ibbenbüren project stands out as one of the largest applications of VMT’s Ring Convergence Measurement System (RCMS) to date, validating its performance in challenging tunnelling conditions. Senceive tilt sensors are fundamental to this process, providing the precise, reliable data needed to monitor convergence, with engineers remotely alerted of any concerning structural changes.
By implementing an automated system that eliminates the need for manual data evaluation, VMT’s RCMS ensures consistent, real-time monitoring, significantly enhancing both safety and efficiency throughout the construction process.
Building the Future with Innovation
As the Ibbenbüren Mine Dewatering Tunnel approaches completion, VMT’s decision to use Senceive’s wireless technology highlights the importance of accurate, real-time monitoring in demanding environments and their commitment to deliver innovative, precise, and reliable monitoring solutions.
