Geotechnical and Structural Engineering

Monitor piles, tunnels, embankments, slopes, sewers, dams, landfills, smart cities …

How does distributed fiber optic sensing help you measure and monitor deformation and temperature events in complex civil engineering projects?

• By detecting small changes, early
• In real-time and continuously
• Over thousands of measurement points
• Remotely
• Over the long term
• Detecting and locating deformation, fatigue and temperature events over long distances
• Providing the real time data you need to accompany digital twins and validate models.

Fiber optic distributed sensing is widely used for structural health monitoring as well as in smart and intelligent structures.

What level of accuracy is achievable?

• deformation with a few micrometers per meter strain accuracy
• temperature events of down to 0.1°C over distances from several m to 50 km from a single interrogator.

Piles and Foundations

Concrete curing

Distributed fiber optic sensing takes the guesswork out of monitoring the temperature of concrete as it cures in large structures, critical to ensuring an energy and cost efficient build.

How?

By measuring temperature (exothermic reaction) inside the structure as it cures, you have the data indicating when curing is complete and you can proceed to the next step, often significantly reducing the time suggested by Standards.
Distributed strain monitoring can detect the formation of thermal cracks in an early phase of the construction.

Pile Load testing

The fiber optic instrumented pile load test reliably evaluates the geotechnical performance of piles. Foundation design can be optimized, resulting in:

• reduced material requirement
• reduced CO2 emissions

while respecting structural performance and reliability requirements.

Fiber optic strain sensing is included in the ‘Specification, requirements and guidance notes’ of ‘ICE Specification for Piling and Embedded Retaining Walls,’ (Institution of Civil Engineers). Guidance for both embedded and surface-attached fiber optic strain sensors is included.
ICE Specification for Piling and Embedded Retaining Walls

PROJECT: Static Pile Loading Tests

Geotechnical monitoring in earth retaining structures

Distributed fiber optic sensing uniquely helps you understand what is happening inside during the construction and settlement of large earth structures, such as slopes, retaining walls, dikes, levees and embankments

PROJECT: Detecting ground movement and deformation of a large earth retaining structure

Construction effect on nearby structures

Instrumenting underground infrastructure provides information about the effect of construction, such as ground movement (strain changes).

Tunnel structural health monitoring

How is the condition of a road, rail or sewerage tunnel monitored without affecting operations?

Fiber optic sensing uses robust inert sensing cables to monitor continuously, in real-time.

The technique is immune to electromagnetic interference (EMI), important when monitoring the condition of train tunnels, underground rail systems and mines.

With a range of 50 km, the fiber optic sensing can be embedded in the structure and attached to rock nails, providing always-on structural health monitoring.

Monitoring during tunnel construction

• Continuous temperature monitoring in shotcrete tunnel linings indicates when concrete curing is complete
• Deformation is measured and monitored continuously. You have the data to confirm when it is safe to move the next section.
• The precision of the system enables shape sensing. Comparing models with actual data provides valuable insight into the behavior of materials and methods. This live data provides feedback for the tunnel’s digital twin and model validation.
• Monitoring strain continuously helps you decide the lining thickness required. Less lining means less concrete, less CO2 and lower costs.

Monitoring during operation

Once installed, embedded fiber optic sensors may be interrogated during the operational lifetime of the asset to detect long-term erosion and other ground or tectonic movements in the tunnel surroundings.

• Continuous strain measurement detects deformation, providing condition monitoring to remote and inaccessible locations.
• Detects deformation and temperature events continuously in lined and rock tunnels

PROJECT: Monitoring sprayed concrete lining deformation during tunnel and shaft construction

ITA President Keynote speech, British Tunnelling Society 2022:
‘Down to the next Level – a role for The UN Global Compact for the underground sector?’
Watch Arnold Dix’s speech:

Slope and ground movement monitoring

Heavier rains and violent storms result in erosion.

In transport infrastructure, cuttings and embankments are at risk of unseen developing landslides. Dikes, levées and steep slopes surrounding water basins, lakes – from erosion. Ports, coastal and sea defenses – from sea level rise and permafrost thawing. Tailings dams deform due to liquefaction and foundation failure.

And when the ground dries out, it cracks, a precursor to landslides.

fibrisTerre systems detect and locate small strain and temperature events over large areas- a single interrogator can monitor 50 km of fiber optic sensing.
When ground movement, settlement or creep and its location are detected with fiber optic sensing, perhaps installed in a geotextile, it can be mitigated and safety management plans revised.

OUR PROJECTS

Installation

The fiber optic sensing cable can be

• embedded into concrete
• installed via microtrenching or geogrids sub-surface
• placed in a groove cut in the asset surface with the sensing cable secured in place with an epoxy filler or cement
• attached to rock nails or other surfaces where the subsurface is not accessible
• direct buried in soil.

For direct burial, a range of ruggedised geotechnical sensing cables is available to suit different applications and terrains.

Soil-anchors may be added to increase strain transfer

Integrating strain sensing cables within smart geotextiles increases strain transfer and extends the area monitored in the soil.