Editing Channel Tunnel (section)

==== Track system ====
Conventional ballasted tunnel track was ruled out owing to the difficulty of maintenance and lack of stability and precision. The Sonneville International Corporation's track system was chosen because it was reliable and also cost-effective. The type of track used is known as Low Vibration Track (LVT), which is held in place by gravity and friction. Reinforced concrete blocks of {{Convert|100|kg|abbr=on}} support the rails every {{convert|60|cm||1|abbr=on}} and are held by {{convert|12|mm||2|abbr=on}} thick closed-cell polymer foam pads placed at the bottom of rubber boots. The latter separates the blocks' mass movements from the concrete. The track provides extra overhead clearance for larger trains.<ref name="bonnett782">Bonnett 2005, p. 78</ref> UIC60 (60&nbsp;kg/m) rails of 900A grade rest on {{convert|6|mm|4=2|abbr=on}} rail pads, which fit the RN/Sonneville bolted dual leaf-springs. The rails, LVT-blocks and their boots with pads were assembled outside the tunnel, in a fully automated process developed by the LVT inventor, Roger Sonneville. About 334,000 Sonneville blocks were made on the Sangatte site.

Maintenance activities are less than projected. The rails had initially been ground on a yearly basis or after approximately 100MGT of traffic. Maintenance is facilitated by the existence of two tunnel junctions or crossover facilities, allowing for two-way operation in each of the six tunnel segments, and providing safe access for maintenance of one isolated tunnel segment at a time. The two crossovers are the largest artificial undersea caverns ever built, at {{cvt|150|m}} long, {{cvt|10|m}} high and {{cvt|18|m}} wide. The English crossover is {{convert|8|km||abbr=in}} from Shakespeare Cliff, and the French crossover is {{convert|12|km||abbr=in}} from Sangatte.{{sfn|Foreign & Commonwealth Office|1994|p=14}}