Sensor Technologies



Track Dam Foundation Subsidence:

The Challenge

Concrete, earthen, or rock-filled dams are put at risk of failure by foundation subsidence. This movement can result from significant lowering of the water table, seismic activity, or the pressure exerted by the water contained by the dam. Tracking subsidence in real time provides an early warning of reduced dam safety and a continuous record of structural health. Traditional methods of monitoring include grouting numerous vibrating wire transducers in series in boreholes. The short actual gage length of these sensors is an issue for very large dam structures. In addition, susceptibility to damage from lightning strikes is a concern in some areas.

Is there a sensor system that can accurately measure subsidence in large dams? Can the system be applied to existing structures? Can the sensors survive a wide range of environmental conditions? Is the system safe to use?

The Solution

FOX-TEK ’s FT ruggedized fiber optic sensors and monitors are part of a complete system with these features. Ruggedized FT sensors contain one or more temperature compensated fiber optic sensors in double walled, waterproof polyethylene tube that is terminated on each end with a threaded fitting. The entire sensor –­­ which is available in gage lengths up to 30 m – can be embedded or each end can be fixed to an anchor point. For the subsidence application, a string of a few sensors linked end-to-end can provide health monitoring for dams 100 m or more in height. A traditional grouted borehole installation method is used. For dam sites without electrical power, a sensor monitor equipped with a radio modem is installed to relay the sensor data to a local field office. The FOX-TEK software is configurable with pre-set threshold values that, when reached, activate an e-mail alarm signal that is sent to various personnel.

Summary of Benefits

  • E arly detection of subsidence effects
  • Timely notification to minimize risk
  • Track changes from seismic events
  Cost Savings
  • M aintenance/repair schedules based on actual integrity
  • Reduced risk of premature structural failure
  • Automated identification of problem areas
  • R educed risk of structural failure
  • Lower risk to maintenance personnel
  • Increased assurance of public safety