High-speed railway track construction in France

High-speed railway track construction is the process by which Lignes à Grande Vitesse (LGV, litt.

The quality of construction was put to the test in particular during the TGV world speed record runs on the LGV Atlantique; the track was used at over 500 km/h (310 mph) without suffering significant damage.

This contrasts with previous French world rail speed record (326/331 km/h in 1955) attempts which resulted in severe deformation of the track.

The first high-speed railway line outside of Japan, LGV Sud-Est, opened to the public between Paris and Lyon on 27 September 1981.

[1] This commitment to a democratised TGV service was enhanced in the Mitterrand era with the promotional slogan "Progress means nothing unless it is shared by all".

The work on a high-speed line (ligne à grande vitesse, or LGV) begins with earthmoving.

The tracklaying process is not particularly specialized to high-speed lines; the same general technique is applicable to any track that uses continuous welded rail.

A special crane unloads the rail sections and places them on each side of the temporary track, approximately 3.5 m (12 ft) apart.

The rail itself is standard UIC section, 60 kg/m (40 lb/ft), with a tensile strength of 800 newtons per square millimetre or megapascals (116,000 psi).

The cranes remove the panels of temporary track, and stack them onto the empty half of the sleeper train.

Next, they pick up sets of 30 LGV sleepers, pre-arranged with the proper spacing (60 cm, or 24 in), using a special fixture.

It then lowers them onto the rubber sleeper cushions, and workers use a pneumatically operated machine to bolt down the Nabla clips with a predetermined torque.

Conventional welding (using some type of flame) does not work well on large metal pieces such as rails, since the heat is conducted away too quickly.

Stress in the rail due to temperature variations is absorbed without longitudinal strain, except near bridges where an expansion joint is sometimes used.

A first layer of ballast is dumped directly onto the track, and a tamping-lining-levelling machine, riding on the rails, forces the stones underneath the sleepers.

The track is qualified at speeds slightly higher than will be used in everyday operations (typically 350 km/h, or 210 mph), before being opened to commercial service.