快猫短视频

AS THE British government grapples with the problems following the failure of
the nation鈥檚 privatised railway line operator, Railtrack, a new technology has
emerged that may bolster the travelling public鈥檚 confidence in the safety of the
troubled network. It鈥檚 an infrared scanning system that, when fitted beneath
ordinary trains, can locate worn-out sections of the track bed, pinpointing
areas where the stony ballast supporting the rails is weak, threatening to
derail a train.

Ballast is needed to spread the forces that trains exert on the ground
beneath the track. It must also allow water to drain freely. But when ballast
gets too old and crushed, things can go badly wrong. In November 2000, badly
draining ballast led to a stretch of line near Northampton subsiding. The
sagging track derailed a passing freight train, which tore up 6 kilometres of
track before it finally came to a halt.

Ballast is built up from three layers of angular granite rocks, which measure
from 2 to 6 centimetres across. Gaps between the rocks allow rainwater to drain
through. But passing trains give the ballast a heavy pounding that gradually
breaks the rocks down into smaller pieces. Fragments start to clog the gaps, so
water can鈥檛 drain through the ballast efficiently.

It is difficult to predict when ballast needs to be renewed, so it has to be
inspected regularly. It鈥檚 a laborious job. Inspectors walk the track at night
when traffic is light to examine it visually. They also test the ballast by
digging pits and looking for damage.

Now Mike Forde and Max Clark at the University of Edinburgh have come up with
an easier way. Using a ground-facing infrared camera mounted on a rail trolley,
they have been able to pick up problem areas by measuring the temperature of the
ballast during the night.

The camera is set to pick up temperature differences as small as 0.01 掳C.
As they moved the trolley down the track they found that degraded ballast was
measurably cooler than sections of track that are in good shape. Forde says this
is because the air gaps in sound ballast act as a heat insulator, so the granite
chips hold the heat of the day for longer.

Fitting the infrared camera to trains could give maintenance workers a way of
continuously monitoring ballast quality across the track network. 鈥淚t could help
you find where you need focus your maintenance,鈥� says Alan Stirling, an expert
in railway engineering at the University of Birmingham. Forde says the system
could be fitted to trains within three years.