Railway construction is linear by nature: work proceeds sequentially along the length of the future track, from its starting point to its end. It depends on many conditions — topography, geology, hydrology, weather and climate, and other natural factors.
Building a railway involves two main stages: earthworks and construction of the track superstructure. Earthworks mean forming and compacting the subgrade, draining it and protecting it against frost heave. Building the track superstructure means forming the ballast bed, laying the sleepers, and laying, fastening and joining the rails.
Railway construction also necessarily includes engineering structures such as culverts, drainage channels, chutes and overpasses, as well as crossings with roads and other railway lines, diamond crossings and turnouts.
Earthworks
The foundation of railway construction is the subgrade. The subgrade is a set of engineered earth structures that serve as the base for the track superstructure. It takes the load from the track panel, the ballast and the rolling stock and spreads it evenly onto the natural ground below.
The subgrade is formed during earthworks. Along the route the ground is levelled, compacted and, where necessary, drained (groundwater is diverted, etc.). Bulldozers build low embankments, cut shallow excavations and benches on slopes, level the ground and backfill — depending on the subgrade type. Soil is placed in embankments in layers, levelled by bulldozers and compacted with rollers, tampers, vibratory compactors and other machines.
Building the track superstructure
As the earthworks advance, track work begins — the set of operations that builds the structural elements of the track superstructure. The track panel is laid directly on the formation level of the subgrade using one of the two methods described below.
- Pre-assembled track panels are laid. The panels are assembled at production bases, stacked and delivered on special flat wagons. During installation the stacks are pulled into the reach of a track-laying crane.
- The track panel is assembled on site: sleepers are laid out, rails are placed on them and fastened.
Each method has its pros and cons. The first is faster on site. However, work can only start from the connection point, because the panels are laid by rail-mounted cranes. It is also more expensive than the second method, since the assembly base may be far from where the track is laid.
The second method is cheaper and allows the track panel to be installed from any point along the route, because it is laid with truck-mounted cranes. Its drawback is a longer construction period. Next, ballast is delivered along the newly laid track in hopper wagons or gondolas and unloaded while the train moves at a set speed. Once the track panel is covered, it is lifted onto the ballast. Layer-by-layer ballasting ends with filling the cribs between the sleepers, bringing the ballast bed to its design dimensions.
Each track work cycle also includes alignment, which brings the track geometry within the limits required for safe running at the specified speeds. After laying, the track is run in by trains. Final alignment and finishing work is carried out before the section is handed over for permanent operation.
The track superstructure must be strong, stable, durable, wear-resistant and economical, so that it ensures safe and smooth train running at maximum speeds under any operating conditions.