JEC COMPOSITES MAGAZINE - Issue #35 - September 2007 - 59

the knitting process. This innovative patented concept makes it possible to monitor the structure throughout its service life by measuring movement within the soil mass. The incorporation of optical fibres makes this geotextile a composite in the strict sense of the term, since it is made up of several different materials: HT PET yarns, a PP non-woven, and the optical fibres, with standard PET yarn used as binding. The main advantage of warp-knitting technology is this very interesting possibility for binding several different materials together to form a system. In geocomposites, the textile can be functionalised in this way to provide reinforcement, separation, filtering, draining, or protective characteristics. On this worksite, the subsidence is due to an old underground passageway located eighteen metres under the road. The passageway accelerates the decompression process on the lower formations and causes subsidence at the surface. A preventive system was put into application when the incidences of subsidence began to increase (four in a single year). The system is based on the capacity of geotextiles to hold the pavement in place even when its lower structure has collapsed. The special geotextile is placed underneath the pavement and anchored underneath the sidewalks on either side of the road (Fig. 7). Examples of geosynthetic systems Some of the geosynthetic systems produced by Texinov are: - a system combining a non-woven polypropylene (PP) material with glass-fibre tows. This type of system is essential for building pavements on erodable soils, as it provides for filtering and separating the soils, and draining out the water. PP is chemically very stable, making it suitable for use in aggressive environments, especially alkaline ones; - a 100% polyester (PET) non-woven system with high-strength, high-mechanical-property PET tows, used for challenging worksites. These geotextiles can resist tensile stresses up to 600 kN/m, and exhibit tensile stiffnesses up to 5,000 kN/m; - a bi-modulus system that serves to make road and railway track underpinnings secure in case of risk of subsidence. Fig. 7: Anchoring trench (BEAM). Focus on the bi-modulus system In Marseille (Fig. 5), a bi-modulus system has been used in a large earthwork project. The road leading from Trois-Lucs to La Valentine is subject to the geotechnical risk of random subsidence, both on the roadway itself and along the road (Fig. 6). The GX 102 bi-modulus geotextile that was used in this specific case is made of 10% polyaramid and 90% polyester. At 0-4% of deformation, it is highly stiff, due to the combined properties of the aramid and polyester, enough to guarantee safety during normal operation. Above 4%, only the polyester tows are under strain, which suffices to guarantee safety during failure of the structure (Fig. 8). Fig. 8: Traction curve. Fig. 6: Photograph of subsidence at this worksite. Fig. 5: Photograph of Marseille building site. When subsidence occurs, the geotextile goes into tensile stress, (effect membrane) holding up the pavement and JEC Composites Magazine / No35 September 2007

JEC COMPOSITES MAGAZINE - Issue #35 - September 2007

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #35 - September 2007