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Mass Transit | MassTransitmag.com | SEPTEMBER/OCTOBER 2014
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Te ground level also shifs natu-
rally from soil movement or vol-
ume changes. Te bridge structure
and train track may displace if the
ground level shifs too dramat-
ically. To mitigate this risk, the
2006 bridge team made ground
modifcations prior to drilling.
However, the modified drill-
ing still caused a number of en-
vironmental changes, most no-
tably ground movement and soil
liquefaction. In turn, the track
on the adjacent 1948 timber tres-
tle displaced (which the Carls-
bad Double Track and Bridge
Project has now replaced). To
further complicate matters, the
geotechnical evaluation con-
cluded that the loose soil in the
area could potentially liquefy
below the water table, which is
the imaginary line separating
ground saturated with water
and unsaturated ground. The
soil, sediment and rocks are full
of water below the water table.
Te Carlsbad Double Track
and Bridge Project designer
has to determine a safe way to
install the substructure piles at
the timber trestle's location. Te
designer has to consider various
pile installation methods to do
The new track
alignment was
in development
while the
existing train
service was
maintained.