| Kuala Lumpur city is sitting
on Karstic limestone geology with high ground water
table. The Special Features of Karstic limestone include
cliffs, pinnacles, cavities, collapsed cavities and
sinkholes. Overlying these Karstic limestones is loose
alluvium from previous tin mining activities.
Due to the nature of the soil condition,
much thought and planning was channeled towards the
selection of a construction method that would have
minimal negative impact on the geological
condition of the soil.
Some Features of Karstic Limestone
It is known that the tunnel boring machine
is the most advanced and cost effective method used
in the construction of tunnel in Europe. However,
TBMs come in a variety of shapes, sizes, using a variety
of technology according to need. For SMART, after
much research, study and survey, the Slurry Shield
TBM was opted for. This machine is designed to overcome
problems of groundwater drawdown which has been identified
as the root cause of incidences of sinkhole appearance.
In terms of cost, the slurry shield
machine is not different from any other type of TBM
but unlike other types, the slurry shield machine
is designed to create a pressured shield made up of
bentonite and air pressure.
This pressured shield is able to counter
balance the pressures of the groundwater and loose
soil acting on the face of the boring machine.