Mining Subsidence Monitoring with Satellite Data

Tunnel Stability

Highlights

Extensive site investigation data allowed the top of chalk and infill properties to be mapped in detail.
The geometrical detail was transferred to a 3D FEA model of the raft foundation.
Differential settlements were found to be within acceptable limits for the glazed facade.
18-month post-construction settlements measured by DInSAR were less than 3mm.
Bending moment and shear force output were used in the structural design of the raft.

Monitoring ground movement above tunnelling operations is crucial for ensuring the safety and stability of surrounding infrastructure. As tunnels are excavated beneath the Earth's surface, they can induce ground settlement or displacement, potentially leading to structural damage, land subsidence, or even surface collapses.

Why Visual Inspections and In-Situ Monitoring Alone Fall Short

Visual inspections and in-situ monitoring may not be sufficient for monitoring ground movement above tunnelling operations for several reasons. Firstly, ground movement can often occur gradually and may not be readily visible to the naked eye, especially in the early stages of deformation. Subtle changes in Surface displacement may go unnoticed until they reach a critical point. The main challenges lie in the identification of the affected areas, the severity of movement, and whether this activity predates or was induced by the construction.

Tunnelling in South Asia: A Unique Challenging

Tunnelling operations in South Asia present unique challenges due to the region's rugged terrain, seismic activity, and the presence of soft, unstable soils in some areas. In such a dynamic environment, monitoring ground movement becomes particularly crucial. As tunnelling operations in this area of South Asia were underway, stakeholders needed a way to monitor the stability of the surrounding ground with a higher level of accuracy than visual inspections allow. Using InSAR technology, Geofem monitored ground deformations along tunnelling alignments with millimetric accuracy. From these insights, stakeholders could detect areas of displacement requiring further remedial attention before critical failures occurred. Areas showing settlement not due to construction of the tunnel were also identified.

Addressing Ground Movement in London's Urban Environment

This project in London faced similar challenges. In a densely populated urban environment with extensive infrastructure networks, historical buildings, and variable geology. Many of London's structures are historic and heritage buildings, which may be more vulnerable to ground movement than modern constructions. Monitoring ground behaviour, therefore, is essential to the preservation of cultural assets, minimising service disruptions and costly repairs. The affected areas can be identified, and the magnitude of the settlements measured using InSAR analysis. Project managers could assess areas of accelerated displacement requiring further attention without needing to disrupt vehicular and pedestrian traffic in a busy city centre.

The Benefits of InSAR for Tunnelling Projects

Millimetric Precision: InSAR technology provides highly accurate measurements of ground displacement, detecting even the smallest movements that might otherwise go unnoticed.
Non-Invasive Monitoring: Unlike in-situ methods, InSAR allows for continuous, remote monitoring without disrupting daily operations or requiring physical access to the site.
Early Detection of Risks: By identifying areas of displacement early on, stakeholders can take preventive measures before the situation worsens, saving time and reducing the likelihood of structural damage or collapses.
Contextual Insights: InSAR helps differentiate between ground movement caused by tunnelling activities and natural subsidence or pre-existing geological conditions, offering a more comprehensive understanding of the ground behaviour.

Conclusion

InSAR technology is transforming how tunnelling projects monitor ground stability, particularly in challenging environments like South Asia and densely populated urban areas like London. With its ability to provide accurate, real-time data, InSAR enhances safety, protects infrastructure, and minimises disruptions. Whether dealing with seismic activity, unstable soils, or historical buildings, InSAR offers a reliable solution for ensuring the long-term stability of tunnelling projects.

For more information on how InSAR can benefit your infrastructure projects, contact Geofem today.

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