Microtunnelling is a technology of trenchless construction of underground utilities (water-, heat-, gas-, sewerage networks, oil pipelines, gas pipelines, cable channels, etc.) in conditions of limited space, where their laying by traditional (open) method is difficult, impossible or might be too expensive.

The method requires no excavation of trenches along the pipe-laying route, and that is why helps to minimise the negative impact on the environment and the usual life running of the area (especially in a metropolitan) during the construction process.

Historically, microtunnelling was designed to perform trenchless piercing for small diameter pipes (up to 900 mm) where human participation is very limited or impossible. Initially the borehole length was barely 100 metres, but with the construction development the method has been improved. Today, with the availability of specialised machinery, the diameter of the puncture can be as large as 2500 mm (even up to 4000 mm) and the distance is more than 300 metres. The maximum tunnel penetration length depends on many related factors: type of soils, associated friction levelling materials, equipment capacity, but the key factor is still the material of which the pipe is made (i.e. whether it can withstand compression pressure).

The development of microtunnelling technology became real due to the introduction of modern equipment: ultra-precise control sensors, progressive control mechanisms and technologies which were previously used in the construction of large-scale tunnels using shields with soil and water loadings. While at its birth the microtunnelling was originally only suitable for linear, precisely controlled depth and gradient tunnelling, the introduction of new technologies, including pressure, deviation, volume, and other measurements, made it possible to extend the scope of microtunnelling. In addition, the geological conditions in which microtunnelling technology can be applied have also expanded. The microtunnelling method enables trenchless laying in geology ranging from sandy rocks to rocky soils, including in weak water-saturated soils.

Here an important role is played by specialists, who must correctly select the type of cutter heads of the equipment for the given type of geology.

The point of the microtunnelling is the use of an underground tunnelling shield (tunnelling machine), which is driven by a jack-up unit (station) located in the start-up pit at the depth of the expected pipeline laying.

The jacking unit transmits a pushing force to the shield, which drills out the ground. While moving ahead, the force becomes more powerful. The pushing action produces a hole equal to the length of the push-through pipes. Inside from the cutting wheel, which drills out the soil, a water is fed to bring the soil to the surface of the shaft in a special sump. In the sump the deposited soil is disposed of and the water can be reused in the push-through process. The gradual movement of the microshield along the planned pipe path ends in the receiving pit, from where it is eventually dismantled. The pipe (collector) stack remains inside the ground.

Importantly, during microtunnelling construction, the entire complex construction process is automated and takes place underground, while all the machine control panels and staff involved are on the surface.

Microtunnelling technology applications:

• in municipal engineering: construction of water supply networks and other various underground utilities, gas manifolds, heating networks and electrical wiring;
• construction of gas and oil pipelines under water bodies;
• connection of an offshore section and an overland pipeline;
• construction of runway crossings, railways and motorways;
• laying of supply lines to objects located in the centre of a body of water;
• providing primary support for large tunnels.

In addition to the wide range of applications, most important advantages of microtunnelling are the high speed of penetration and, as a result, short project complementation in time.

BELTRUBOPROVODSTROY JSC implemented some significant projects using microtunnelling technology. Among them there was the project: “Expansion of the Unified Gas Supply System to provide the gas supply to the South Stream gas pipeline”. BELTRUBOPROVODSTROY performed the construction works of the underwater crossing through the Proletarski Reservoir with total length  1250 m, diameter 2000 mm by Microtunnelling Technology. (2016, Customer: Gazstroyproekt, Russia)

*the photos are for illustrative purposes only