Chatswood - Epping
Rail Tunnel
 For
the Chatswood to Epping rail tunnel in Sydney, Australia
Thiess Hochtief the main contractor had several options
to fix the rail lines to the concrete track slab. Very
early in the process it was decided that the best method
was using Delkor rail base plates.
There are two basic type of base plate.
The first is for fixing the rail to a “floating”
track slab and the second is for fixing the rail to
a “fixed” track slab. A “floating”
track slab is for where the tunnel passes under high-density
housing and the “fixed” is for not so noise
critical areas.
A “floating’ track slab is, as the name
suggests, a concrete slab, 20 metres long by 2.1 metres
wide and 600mm. thick. After pouring, it is jacked up
20mm and rubber bearers inserted to insulate it from
the tunnel base. Each slab is about 20mm. from the next
and they are held in position by 3 no. 600mm. by 600mm.keys.
The “fixed” slab is poured directly on to
the tunnel base.
The next problem was securing the base plates to the
concrete. Again there are two options. One is to set
the base plates in position and pour the concrete to
the required height around the hold down bolts. The
other option is to pour the concrete and drill holes
later on for the hold down bolts. There are obvious
advantages and disadvantages for both methods and it
was decided for the majority of the “fixed”
slab that the first option would be appropriate and
for the “floating” track slab and the remainder
of the “fixed” track slab that drilling
the holes after curing and jacking would be appropriate.
There was 5.5kms of “floating” track slabs
and 3.1km of DFF driill and grout slabs in the 26 km
tunnel requiring 96,000 50mm. diameter holes a minimum
of 135mm. deep. To maintain the tunnel programme 1000
holes had to be drilled per day.
To get the job done in a timely manner and because of
the accuracy specified, +/- 1mm in either direction,
we decided at an early stage that we had to use a multi-head
drill rig. Our calculations were that we needed a rig
that would simultaneously drill 16 holes. The logistics
were difficult. No manufacturer that we contacted had
ever built such a machine or had even heard of one being
built. We were working up to two kilometers from the
tunnel entrance. Water was supplied to the job; a 75kVa
generator supplied power. Slurry was to be disposed
of using the tunnels’ environmental systems. There
was 75 tonnes of concrete cores to be transported to
the surface and disposed of.
The result: All the holes were drilled to within the
1mm tolerance. If site conditions were to specification,
we were able to drill our 1000 holes per day. The 16
head-drilling rig worked better than anticipated.
Click
here to download pdf detail sheet (pdf~116kb)
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