One of the methods currently being proposed for combating the risk of accidents due localised sinkholes under road and railway embankments is to place a reinforcing geosynthetic at the base of the structure. To develop a method for designing this type of installation, full-scale tests were performed on the TGV highspeed train line in the Drôme region of SE France. From the results of these tests, it was possible to determine specific subsidence mechanisms associated with a membrane-type behaviour of the geosynthetic reinforcement for each material studied, and consequently to propose an appropriate design method. The assumptions of this method differ in certain respects from those usually made in certain other countries. To check the validity of the observations, a new series of full-scale tests was carried out at an experimental site fitted with measuring instruments and using different types of fill material.
The progressive growth in road and rail infrastructure in industrialised countries has resulted in roads and tracks being laid in high-risk areas likely to be subject to localised forms of subsidence. The presence of natural or artificial underground cavities relatively close to and possibly extending up to the surface means that there is a permanent risk in operating the infrastructure in question. While large-diameter cavities can in general be detected, there is currently no reliable method for systematically detecting the presence of smalldiameter cavities at medium and shallow depths prior to carrying out construction work. The purpose of the reinforcement is, on one hand, to alert operators that a sinkhole is beginning to form and, on the other, to limit surface subsidence to reasonable levels until backfilling and repair work can be carried out. Generally speaking, this technical solution should only be considered as temporary, pending complete rehabilitation of the site.
