Detecting Subsurface Tunnels Using Gravity
Non-invasive void detection for construction, rail, and security applications
The Challenge
Subsurface tunnels and voids—whether historic mine shafts, construction features, or hidden infrastructure—pose serious risks to engineering projects, transportation networks, and security operations. Traditional survey methods often struggle to detect these voids non-invasively, particularly when they are deep, narrow, or located in complex terrain.
Whether for rail construction planning or military-grade tunnel detection, the need for a portable, scalable, and reliable sensing method is clear.
Survey Context: Global Centre of Rail Excellence
In 2024, Silicon Microgravity partnered with the Global Centre of Rail Excellence (GCRE) to conduct a field trial over a known subsurface tunnel anomaly. The goal: demonstrate whether our latest resonant MEMS gravimeter GAIA-FIELD could detect an air-filled void with high precision and speed—under real field conditions.
Key anomaly characteristics based on previous borehole data:
- Air-filled tunnel approx. 2 m wide
- Estimated at a depth of ~12 m
- Expected gravity anomaly: 14 microGal
Field Trial Approach
Three SW–NE survey lines were taken each with 15 stations spaced 5 m apart.
Two lines were close to existing borehole locations, a further line was based on extrapolation of the possible void
GAIA-FIELD achieved< 5 µGal resolution with <90 seconds measurement time per station despite high environmental noise from local plant
Three repeat measurements per station were taken to ensure data reliability
The detected gravity anomaly closely matched modelled response for the void
This field methodology offers a scalable and cost-effective method for void detection, adaptable for construction, defence, and security.
Best Practices & Considerations
Choose your station spacing based on the estimated size and depth of your target anomoly
Once an anomoly is detected consider using repeat measurements or tigher station spacing to refine results
If your gravimeter doesn't provide automated corrections for tide, elevation, drift and terrain ensure these are applied during post-processing
For deeper or more complex structures, gravity data should be integrated with other geotechnical data including magnetics, inSAR, LiDAR, seismic and ground penetrating radar where available.
Technology Enabler: GAIA-FIELD
The GAIA-FIELD MEMS gravimeter brings lab-grade sensitivity into the field: <5 μGal sensitivity in under 2 minutes per station. Modern ruggedised and compact solution designed for single-person use. Ideal for pre-construction, geotechnical, or security-focused surveys.
Learn More
Gravity-based tunnel and void detection has clear applications across sectors:
- Rail infrastructure & construction planning
- Engineering and environmental consulting
- Government and defence tunnel monitoring
- Pre-excavation hazard assessment
- Long-term network integrity monitoring
Contact our team to discuss your field trial needs, or to learn how our existing field gravimeters and future mobile gravimeter solutions can extend your gravity capabilities.
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