What Does Large Diameter Tunneling Mean?
Large diameter tunneling refers to tunnels that have a diameter of 4 meters or greater that are excavated using tunnel boring machines (TBM).
Improvement in TBM technology along with past experience is allowing the safe and successful installation of these large-diameter tunnels.
Large diameter tunneling fulfills the need to accommodate larger infrastructure such as multiple traffic lanes and railroad tracks, and in some cases where both can be combined. This is especially useful in cities where land space for surface infrastructure is limited.
Trenchlesspedia Explains Large Diameter Tunneling
Large diameter tunneling allows for parallel operations to be undertaken during the construction phase itself, unlike in smaller diameter tunnels that only allow activities to be conducted in series after each operation is completed.
With advancements in technology, it is now possible to use large diameter tunneling in challenging ground conditions using close-faced pressurized TBM's. This kind of TBM was originally developed specifically to operate in soft clays and in loose cohesive soils below the groundwater table. Now they are also used to excavate through mixed-face conditions of soil and rock and through full faces of rock.
Hybrid TBMs have also been developed that combine close-faced pressurized TBM and earth pressure balance TBM. The hybrid machines can operate in either mode depending on the ground conditions.