DTSS- Changi Tunnel
Shield Tunnelling was used in the construction of DTSS-Changi Tunnel.
Principle of Shield Tunnelling:
There is an over-cut where the diameter of shield including the thickness of skin is more than the diameter of tunnel. On top of tunnel, there is always tendency to over-cut in order to reduce friction of shaft during tunnelling works.
The push cylinders push the shield forward against frictional forces of the soil and against the required support pressure. The surface of the last segmental lining ring built inside the shield tail serves as abutment for the push cylinder shoes.
Shield Tunnelling provides shelter for the workforce.
a. Mechanization and high advance rate.
b. Exact tunnel shape, over-cut is small.
c. Least impact on surface structures &
d. High level of safety for personnel.
a. It cannot handle mixed soils. Shield Machine can be successfully used to tunnelling either in soft soils, or in very hard soils. But the same machine cannot handle changes in soil conditions.
b. Expensive for relatively short lengths of tunnelling.
c. Long preparation time, as the manufacturer has to deliver and assemble the tunnelling machine.
d. It can only be used for fixed shape sections and not suitable for stations that require different shapes.