TBM, the underground giant

The story has begun long long time ago
when the ground had became so congested especially in urban cities...

Some chose to go up
and that's why some of those magnificient bridges originated

Others chose to go down
but seldom do people notice the beauty of tunnel...
(and probably why geotechnical engineers are being neglected,
not to mention engineering geologists!)

Meanwhile, the underground option takes the lead
Thanks to technology advancement to overcome difficult ground condition, thus improving the efficiency during construction and reducing cost.
In addition, the public nuisance caused by the construction is lesser as compared to above-ground works, as people are hardly visible to the construction works beneath the ground.

The construction cycle is greatly reduced by these giant machines -
TBM (Tunnel Boring Machine)
There are different types of TBM, which works in soft (soil) , hard (rock), or mixed (soil and rock) ground.

Although I don't have the chance to work in tunneling works (well, girls are not welcomed...), it's a great opportunity to visit the fabrication workshop in Guangzhou to take a look at these giants.

I'm not an expert in these machines, so it's just a brief outlook of what these giants are like...

Mixshield TBM, for tunneling in ground with complex geology (soil and rock)
The machine is so long (it's almost 200m in length)


Double shield TBM (fabrication in progress), for tunneling in hard rock
This will be used later in one of the Hong Kong tunneling projects


Though these machines have greatly improved the production efficiency in tunneling works, the choice of machine with a good understanding of ground condition is still vital.
An example is the Hsuehshan Tunnel in Taiwan, where the wrong machine was chosen and the complex geology was not recognised, causing significant delays and loss of life in several tunnel collapses during construction. In later stage of the project, conventional drill and blast option was adopted to replace the TBM method. Finally, the 12km long twin tunnel took 14 years to complete.

In the end of the day, we cannot just rely on technology - and that's when the engineering judgement plays its part!