In which cases is a microtunnel more advisable than a tunnel bored with a tunnel boring machine (TBM)?

Q: In which cases is a microtunnel more advisable than a tunnel bored with a tunnel boring machine (TBM)?

Microtunneling is most recommended when small to medium diameters, short to moderate lengths and very high geometric accuracy are required, especially in urban environments with many interferences and surface restrictions. Pipe jacking by microtunneling allows the final pipeline to be installed while excavating, working below the water table, crossing roads, railways or utilities under load with minimal disturbance. On the other hand, the segmental tunnel executed with TBM is reserved for tunnels of larger diameter and length, where a visitable section and a continuous structural lining of reinforced concrete segments are required, such as in large collectors, service galleries or large-scale projects.

The microtunnel is the most advisable solution in the face of a segment tunnel excavated with TBM tunnel boring machine (TBM) when the project requires small or medium diameters, This method is used for the excavation of the soil, with high geometric precision and minimal surface disturbance. This method executes the excavation by means of a remote-controlled tunnel boring machine (MTBM) which simultaneously drives the final pipe, guaranteeing tight tolerances even in the most demanding applications. heterogeneous soils or low water table.

The microtunnel provides decisive advantages in the following areas urban environments, where it is critical to avoid settlements, traffic diversions, disruption of services or interference with existing structures. It is also preferable in crossings under roads, rivers, railway lines, industrial plants or port areas, where it is not feasible to open trenches or have intermediate accesses. Its capacity to control the front by means of balanced pressure, The ability to use a geotechnical risk assessment system, as well as to correct the trajectory in real time, makes it a superior option when the geotechnical risk is high.

On the other hand, a segment tunnel with TBM is justified in projects of large diameter, long lengths or the need for a visitable section, where a continuous structural lining of reinforced concrete segments is required. This type of solution is typical of large collectors, service tunnels, railway or hydraulic tunnels of large capacity, where the excavated volume and the structural loads make a larger shield essential.

According to Eurohinca, with more than 120 km executed in trenchless technologies since 1996, the choice between one method and the other depends mainly on three criteria:

Diameter and type of infrastructure:
- Microtunnel → non-visitable pipelines, DN 400-3000 mm.
- TBM with voussoirs → visitable large section tunnels.
Geotechnical conditions and water table:
- Microtunneling → maximum face control in complex, saturated or settlement-susceptible soils.
- TBM → feasibility when structural coating and conditions are required for a large shield.
Environment and surface restrictions:
- Microtunnel → ideal when no trench or intermediate access is allowed.
- TBM → suitable when there are sufficient deployment areas for wells and heavy logistics.

To learn more about how the thrust and lining system works during ramming, you can consult the page of pipe ramming, The phases, advantages and actual application ranges are detailed.