Solution


A Sensor-Enabled Geotextile

Traditional attempts to monitor soil strain and temperature in-situ have been met with instrumentation problems as well as other significant challenges: difficult and costly installations, construction delays, installation damage, excessive maintenance, poor accuracy, and only short-term results.

The patented TenCate GeoDetect® system starts with a unique design that embeds fiber optic sensors into a composite geotextile during the manufacturing process. The geosynthetic composite has a highly efficient interaction with the soil and therefore can accurately measure soil strain. Thus, the TenCate GeoDetect® sensor-enabled composite offers an accurate measurement system that can be easily adapted to monitor a wide variety of geotechnical engineering structures. TenCate’s exclusive Distributed Anchoring System enables the sensor-enabled geotextile to have an intimate relationship with the soil. Strain and temperature information is transferred from the soil directly to the fabric and to the fiber optic with nearly perfect accuracy.


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Figure 1. The TenCate GeoDetect® composite geotextile has fiber optic sensing cables embedded onto it during the manufacturing process.

Once installed, the sensor-enabled geotextile communicates the soil strain and temperature data to the TenCate GeoDetect® system’s interrogator equipment. Soil strain as low as 0.02% can be measured, and with the proper software, changes in temperature can be monitored at 0.1C with a spatial resolution as precise as 0.5m to 1.0m.

The TenCate GeoDetect® system is comprised of the sensor-enabled geotextile, data acquisition instrumentation, data logging, visualization, alert and reporting software as shown in figure 2.


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Figure 2. The TenCate GeoDetect® system components

This actionable information can be used for a number of functions:

  • Field performance monitoring
  • Early-warning system
  • Structural health monitoring
  • Observational Design and Design validation

With the TenCate GeoDetect® system, engineers now benefit from an in-depth look into the integrity of geo-structures. They can utilize geosynthetics in applications that were previously not considered because of insufficient design knowledge and long-term performance uncertainty.


Fiber Optic Sensing Technology

The TenCate GeoDetect® system can utilize three different fiber optic sensing technologies:

  1. Fiber Bragg gratings (FBG)
  2. Distributed Scattering
    1. Stimulated Brillouin Scattering
    2. Raman Scattering

Fiber Bragg Gratings


Fiber Bragg Gratings

Strain sensors that form an intrinsic part of the system are incorporated in the cable using Fiber Bragg Gratings (FBG) technology to detect strains in the geosynthetic. Any stresses exerted in the geosynthetic will cause a wavelength shift in the sensor that can then be related to a corresponding strain as shown in Figure 3.

By using different wavelengths (λ1, λ2, λ3 etc), signals of various FBG sensors can be identified and distinguished. Because each sensor has its own unique wavelength, the sensors can be integrated in series along one optical fiber line. In this way multiple sensors can be measured simultaneously and the location of the strains localized within the soil structure.


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Figure 3. The principle of Fibre Bragg Gratings (FBG) in TenCate GeoDetect®.


Distributed Scattering

Distributed Scattering is best suited to monitor projects with large surface areas, generally over 100 meters in length. (Principle: frequency analysis of retro diffused (laser) signal. Brillouin and Raman scattering is a natural scattering process associated to the propagation of light in a medium like an optical fiber.)

The interaction results in the generation of scattered light (Brillouin or Raman components) which shows either a frequency (or wavelength) shift for the Brillouin component, or a signal amplitude shift for the Raman component, compared to the light causing the interaction. The principle is based on the analysis of the Brillouin or Raman scattered light in optical fibers to perform strain and temperature measurement. This can be achieved since the Brillouin and Raman shifts depend on the acoustic velocity of the medium, which is temperature or strain/temperature dependent as shown in figure 4.


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Figure 4. Principle of Brillouin scattering in the TenCate GeoDetect® system.

  • Stimulated Brillouin Scattering:

    Brillouin Scattering technology is used to obtain changes in strain and temperature over long distances. Individual sensors are not required using Stimulated Brillouin Scattering. Standard fiber optic cables, instrumentation equipment and software provide the strain and thermal data. With the proper instrumentation, strain measurements as small as 0.1% can be obtained with a spatial resolution of 1.0 m at a distance of 20km. Temperature changes of 0.1°C can be obtained at similar distances.
  • Raman Scattering:

    Raman Scattering technology is used to obtain very minute changes in temperature. Individual sensors are not required using Raman Scattering, however, special fiber optic cables, instrumentation equipment and third party software are required to provide actionable thermal data. Changes in temperature as precise as 0.1 °C can be obtained using this specialized equipment. For TenCate GeoDetect® applications, a 0.1 °C temperature resolution with a spatial resolution of 1.0m at a distance up to 10km is sufficient for monitoring small leaks in levee applications. 

Data Acquisition Software

Data acquisition software is included with every TenCate GeoDetect® solution. Each TenCate GeoDetect® system comes with a standard software package designed to operate the appropriate instrumentation equipment. Our team optimizes this base software for each project. This software can also be customized to meet the specific needs of each project providing the user with alarms, notifications, web interface and reports.


System Installation

No monitoring solution would be complete proper installation. The TenCate GeoDetect® Team of Systems Integrators are experts in installing fiber optic sensing technologies and data acquisition systems around the world. We provide the complete package of products and services to provide you with a turnkey solution.


Advantages of the TenCate GeoDetect® solution

TenCate GeoDetect® System Conventional Instrumentation (Electromechanical Strain Gauge)
EASY TO INSTALL Very cumbersome and difficult installation due to application of adhesive of each ESG on geosynthetic. Calibration needs to be carried out on every ESG to maintain accuracy of measurements.
MULTIPLE MEASUREMENT POINTS ALONG ONE SINGLE FIBER OPTIC LINE Each sensor must be individually wired. Complex installation for a multiple sensor application.
Economical due to the low cost of sensor preparation and installation procedures Very high cost of sensor preparation and installation by highly skilled technicians.
HIGH INSTRUMENTATION ACCURACY Poor accuracy due to difficulty in calibration. Also depends on electrical resistance due to environmental factors and length of wiring.
FREE FROM ELECTRICAL OR ELECTROMAGNETIC INTERFERENCE. Influenced by electrical and electromagnetic interference.
WATERPROOF Non-waterproof and ESGs need to be individually protected.
DURABLE AND LOW RISK OF MALFUNCTION ONCE INSTALLED Non durable and high risk of malfunction due to breakage, corrosion, short circuit and installation damage.
PROVIDES LONG-TERM PERFORMANCE Normally short-term monitoring only
VERY LONG DISTANCE MEASUREMENT FOR HUNDREDS OF METERS. Local measurement
BG-GeoDetect