Characteristics
This method starts an enlarged shield from the starting base at a given point in a shield driven tunnel and excavates the tunnel longitudinally to enlarge the cross section in the tunnel.
- Cross section can be enlarged for a desired length according to the use of space.
- Circular cross section created after enlargement ensures structural stability.
- Eccentric enlargement of cross section is possible in all directions.
- The method offers even greater economy and shorter construction period in tunneling at greater depths.
- Work is carried out exclusively in the tunnel with no adverse effects on surface traffic or the environment.
Variations of construction method
One of three construction methods can be selected according to the length of the tunnel to be enlarged.
| Type 1: | Combination of circumferential shield tunneling system and enlargement shield tunneling system |
|---|---|
| Type 2: | Combination of circumferential shield tunneling system and enlargement excavation system |
| Type 3: | Circumferential shield tunneling system |
Examples of tunneling equipment
-
- Circumferential shield machine
-
- Enlargement shield machine
-
- Enlargement slurry shield machine
Mechanism of tunnel driving
- Excavation by a circumferential shield machine
(construction of the base for starting an enlargement shield machine)
- Assembly of an enlargement shield machine
- Tunneling by the enlargement shield machine
Applications to actual tunneling
Applications to actual tunneling
| Use | Outer diameter (mm) | Length (m) | |
|---|---|---|---|
| Primary segment | Enlarged segment | ||
| Underground cable tunnel |
6,600 | 7,800 | 24.1 |
| Utility tunnel | 6,600 | 9,200 | 29.5 |
| Sewer tunnel | 6,000 | 8,709 | 11.3 |
| 2,000 | 3,150 | 2.6 | |