Floating track slab

The rail is mounted on a concrete track slab. A resilient layer or spring system supports the slab.

Examples of these systems can be seen on the Japanese Shinkansen, sections of Hong Kong MRT, and in some Docklands Light Rail tunnels. The Channel Tunnel Rail Link has floating track slab over the East Coast Main Line bridge outside St. Pancras Station.

There is a wide spectrum of floating track slab types available ranging from simple slabs cast on a rubber membrane, through to sophisticated sprung systems such as manufactured by Getzner.

Turnouts, crossovers and rail expansion joints can all be mounted on floating track slab.

System Components

A floating track slab system consists of rails mounted via baseplate fasteners on a pre-cast or in situ reinforced concrete slab.

The slab is supported off the foundation slab by a resilient layer. This can take the form of:

• Resilient membrane
• Bituminous material
• Bearings
• Springs

The choice of system will usually depend on acoustic performance and cost. Compared to other slab track systems, floating slabs generally require greater construction depth (particularly those supported on springs and bearings).

System Performance

Floating slab systems have been in use for many years. The most notable example is the Japanese Shinkansen where pre-cast slab sections are supported on a resilient bituminous grout. This track system has proven reliability for operation on high speed rail lines.

Other systems such as Getzner floating slab tend to be applied over short lengths where a high level of acoustic mitigation is required.

Construction Issues

For a simple system, a reinforced concrete trough is lined with a resilient membrane. An in situ reinforced concrete track slab is then cast directly against the membrane. Trackwork can be installed by a drill-and-fix technique, with grouting beneath baseplates. Alternatively, “top down” construction can be used with the slab cast around the baseplate fixings.

The more complex systems involving bearings or springs typically use pre-cast track slab sections. Restraining plates are usually required to ensure transmission of longitudinal and transverse forces.

Maintenance Issues

For systems using springs or bearings, access to these for routine maintenance or replacement must be incorporated into the slab design.

Acoustic Performance

Floating track slab systems can offer very high levels of mitigation against ground-borne noise and vibration. The high mass of the slab contributes to the damping of vibrations. A high degree of resilience can be introduced into the bearings or springs, without adversely affecting the rail seat stability.