Feeling the earth move

EUREKA project E! 2579 GEODETECT has developed an effective and totally novel product for detecting soil subsidence – vital for avoiding costly damage to buildings and infrastructures. Since its development the product has been installed in parts of the French railway system and also around the world in key supporting structures such as bridges and embankments.

Existing monitoring systems for subsidence depend on visual inspection; but by the time visual assessment can be made, the damage is well advanced and repair is costly. Subsidence is a particular problem for railways, where even a few millimetres’ change in track level could have disastrous results, particularly for the coming European high-speed rail network. Damage repair or alternative structural solutions, like building reinforced bridges at critical locations liable to subsidence, both present very high costs.

High-strength matting

The GEODETECT project set out to add a sensory system to an existing material called geotextile. This is a non-woven, fibrous matting made of high-strength polypropylene fibres, reinforced with high-strength polyester yarns. With its high mechanical strength, resistance to mechanical and chemical damage and long life, the geotextile matting was already used without sensors as the foundation for roadbuilding, where it reinforces the soil beneath the gravel layers and gives it added strength. Dr Alain Nancey of project partner Bidim Geosynthetics explains: “Adding sensors linked by optical fibres into the geotextile enables hundreds of them to be installed quickly into the ground, in a critical area where there is risk of collapse. If a cavity appears in the soil under the geotextile, the resulting lengthening of the fibre in the matting will be detected by the sensors and be relayed to the monitoring system. In the case of a railway, for example, the affected track section can then be isolated and repaired quickly before real damage is done.”

The two partners involved in the project were Bidim Geosynthetics from France (now part of Tencate Geosynthetics), and IDFOS (now FOS&S) from Belgium which had already been involved in monitoring the structural soundness of buildings and bridges.

The GEODETECT product has been of great interest to the French national railway company SNCF, and has already been put into use in a section of railway line in mid-France. The project has also led to the development of small geodetect strips, in contrast to the original 5-metre-wide rolls, which can be inserted into built structures like retaining walls, dams and embankment reinforcements. These have been used in about 15 critical locations throughout the world. Further opportunities are opening for the large-scale matting, particularly with the building or conversion of railways to take high-speed trains.