MINITUNNEL  T.A. 1200 ÷ 4200

On straight tunnels with diameter between 1200 and 3500 mm and length exceeding 200 – 250 metres, the pipe jacking system is generally used.
Here the tunnel lining is constructed outside in prefabricated rings from 1500 to 2500 mm in length.
The main jacking station inside the well acts, by thrust jacks, on the last ring lowered from above, gradually driving the entire lining, and thus the machine, along the tunnel.
The friction developed between the lining and the tunnel surface limits the length of lining which can be installed using a jacking station to 40 - 70 metres.
Therfore, in tunnels exceeding 40 - 70 metres of length, intermediate jacking stations are required.
These consist of segmented steel rings and a set of hydraulic rams feeded from outside.






In this case the tunnel lining is built internally using segmental rings.
The system is therefore fitted with a segment handling system for advancing and placing of segments inside the tunnel which must be of sufficient size: diameter exceeding 3500mm.
The machine is advanced by a set of hydraulic rams between the shield and the fixed lining of the tunnel.
This system can be used to excavate and line tunnels up to several kilometers in length, which do not have to be straight.


Advantages and Performance

These machines allow tunnels to be cut without interrupting the activities normally carried out on the surface above the area where digging is taking place.
They can be used for :
- Sewers, irrigation pipelines and drinking water mains ;
- Tunnels to take utility lines ;
- Repair of old pipelines ;
- All underpasses of special importance for roads, railwais, airports, town centres, buildings etc.
The choice between the bucket for use with soft materials and the cutting unit for compact materials having bearing strenght 250 daN/cm² allows the machine to work at top efficiency. No skilled operatives are required for changeover of these assemblies and the procedure takes only a short time ( 4 - 8 hours ) ; it can be carried out in the tunnel. The advance rate is approximately 1,5 m/h with the bucket and 1 m/h with the cutting group.