A new Pendolino train was successfully tested by Czech Railways at up to 237km/h (147mph) on a trackbed with the sub-grade stabilised by Tensar bi-axial geogrids, and laid over soft ground with low bearing capacity. Although the normal maximum speed for the Czech Railways is 160km/h, in November 2004 a test was authorised that took the train from 160km/h to 230km/h in three minutes, and then recorded a stopping distance of 1,800m from 220km/h to 0km/h.
Tensar geogrids have been utilised to enhance the bearing capacity of soils on many sections of the fourth pan-European corridor line between Èeská Tøebová, Brno and Bøeclav.
With the standard maximum speed of 160km/h (99mph), the track structure had to have an appropriate bearing capacity beneath the ballast layer. However, the sub-grade stiffness modulus was as little as 15Mpa in many sections, and the water table was also high.
Use of Tensar geogrids enhanced the bearing capacity and improved track geometry enabling the rail network to be modernised at minimum additional cost despite the poor ground conditions. The Czech railway system has undergone extensive modernisation with the construction of the fourth and sixth pan-European corridors; the work commenced in the mid-1990s and is scheduled for completion in approximately 2015.
The Tensar bi-axial geogrid manufacturing process produces a unique grid structure, consisting of full-strength junctions and stiff ribs, which present a thick, square leading edge to the aggregate used in trackbed construction. This allows the aggregate particles in ballast or sub-ballast to grip the geogrid and forms an effective mechanical interlock.
The interlock prevents lateral movement and dilation of the aggregate particles, so that a very high effective angle of shearing resistance is mobilised, and the load bearing capacity of the aggregate layer is greatly enhanced. This enables smaller volumes of aggregate to be used and avoids the requirement for heavy conventional solutions such as piling and rigid concrete structures.