main rail line between Dublin and
Belfast in Ireland it’s 625 p.m. on a
Friday evening and the trains before and
after you are full commuter trains heavy
with passengers as you drive over
malahide viaduct a bridge that takes you
over a big estuary you notice the water
splashing a little bit higher than usual
you look out the window and your stomach
drops
you notice part of the bridge you’re
driving over crumbling into the waters
below
there’s only track holding up you and
the other passengers from falling into
those waters this actually happened on
August 2009 the fourth pair of malahide
rail viaduct collapsed into Broadway
meadow estuary luckily in this instance
the driver managed to coast the train
safely over the bridge and called it in
Holts the passing of any further trains
but this was very nearly a much larger
tragedy with human life at risk now the
cause of this particular failure was
judas scour scour is where the ground
material in a river or estuary is worn
away a kind of erosion that forms a hole
around the foundations of a bridge so
when it’s no longer supported it’s at
risk of collapsing what’s scary is that
this isn’t an isolated incident you can
see that there are actually many more
cases of this in the UK periods of heavy
flooding in the last few years have
caused collapses in Scotland Cumbria the
south of London and the South of England
there was even just a bridge collapse
last month it’s actually kind of
terrifying how many things fall down
around us take this example in August
2007 the i-35w Mississippi River Bridge
collapsed it killed 13 people and
injured a further 145 so after the
collapse a forensic investigation was
undertaken and yes by forensic invest
I mean in a similar way you think of a
crime scene where you carry out forensic
investigation to figure out what
happened engineers we also carry out a
forensic engineering activity to try and
figure out why major structural collapse
has happened it’s a little bit like CSI
for bridges only no one’s asked me to
start a hit new TV show yet back to my
story um so this particular bridge
failed because certain plates these
plates started to bow out and then one
day they suddenly collapsed taking the
whole bridge down with it the scary
thing about this is that looking at
photos taken during an inspection four
years before this collapse revealed that
you could see the bowing of this plate
now it was only a few millimeters but
the scary thing was it was there we just
missed it by eye so if you think how did
we miss that well actually most
countries carry out inspections by a
period of standard annual or – yearly or
sometimes six yearly visual inspections
so someone like me I’ll come along with
some drawings and we’ll look at the
bridge and we’ll mark up the defects we
can see take a few photos that kind of
thing but it inherently relies on
someone being able to spot signs of
distress or unusual behaviors before
they reach this kind of catastrophic
stage so is there something else we can
do
is there something where we could
remotely munde our bridges something to
give us a little bit of a hand could we
say use our eyes in the sky to help us
out another issue with our visual
inspections is that things happen
between these visual inspections things
like this are strong weather effects
we’re seeing the effects of climate
change quite strongly periods of heavy
rain and heavy snow ice and storms
temperature affects both hotter and
colder that we’ve never seen before to
put it simply our structures are seeing
a whole bunch of environmental
conditions they weren’t actually
designed to experience so if you think
about the snow and ice for ice we throw
around salts on the road to melt it so
that we can drive and walk safely but
salts actually accelerate the process of
corrosion
so we’re actually deteriorating our
bridges are reinforcing in our steel
work at a faster rate if we think back
to our example of our failure more
floods and faster flows means that we’re
accelerating this process of scour and
how do we monitor for scour well we
actually send the diver there so that
someone can go see firsthand exactly
what’s happening but even this has
limitations you can’t send a diver
during a flood event itself for danger
of the diver and lack of visibility even
when the waters are lower the diver is
at risk because well you’re sending
someone down to a structure that could
potentially collapse on them and then
finally even if everything is fine and
you send a camera down to look if
there’s a little bit of material that’s
loose that covers that hole you may not
even see that there’s a difference so
again we need a remote way of doing this
we need something that can detect tiny
millimeter levels of movement that our
eyes miss and lucky for us we have some
friends we have satellites so I’m a
civil engineer I work in the design
building maintenance and construction of
bridges and rail lines and schools and
hospitals and water treatment and energy
sources the things that are all around
us that you take for granted but I’m
also really passionate about keeping our
cities safe and keeping them healthy
enough to be able to stand withstand
these kinds of these climate changes so
now I’m working in the space sector I
work with organizations like the German
Aerospace Center and the satellite
applications catapult to use satellites
to try and help us prevent some of these
catastrophic failures so I specifically
use a technique called radar
interferometry this is where satellites
like these ones pass over the earth
they send pulses of electromagnetic
radiation which hit the surface and are
reflected back up to the satellite
giving a bit of information so every
time one of these satellites passes say
over this building it sends a signal
which is sent down bounces back and sent
back up again the next time it comes
back it does that again and this time it
takes for the signal to fly down and
then come
tells us a little bit about how much
that’s moved since the previous image so
how do we use that practically well
historically it’s been used in
large-scale deformations
such as volcanoes or earthquakes but
what’s really exciting is that the
resolution is finally small enough that
we can do things at a city scale or
maybe even a single building or bridge
scale so might be easier if we just look
at a simple example this is a piece of
work done with telus passio which is
looking at London so the river you can
see is the Thames and this is the area
just north of these little dots
represents a reflection point
now these reflection points are tracked
over time and so these are now been
color-coded to show movement as
millimeters per year over over time the
red dots represent things that are
sinking green is stable and if there was
blue it would be uplift so you can see
that an area just north the o2 is
rapidly sinking now it looks a little
bit alarming but scale is everything
here the red dots show movement that’s
no larger than the size of this penny
really tiny um so then you say well why
do we care if you think about say taking
off the size of a penny off one of the
chairs of your leg you’ll notice the
difference similarly if we have part of
our buildings sinking it’s not the same
effect but there might be a problem and
it’s something that we need to be aware
of in this particular case what happened
here was the construction of a new rail
line underground tunneling where they
dug and put in a shaft to install that
shaft they needed to D Ward remove the
water from that area when they remove
the water the whole area sunk and when
they returned the water this actually
rose back up again so then how does this
apply for our bridges well if we can
start monitoring certain points along a
bridge using our radar then we might be
able to tell a little bit when it’s not
doing what we’re expecting if we combine
structural knowledge to to plan how it
should behave can we spot things that
that are a little bit off I don’t know
if you know this but bridges aren’t
actually
designed to stay still they’re actually
designed to expand and contract they
have expansion joints and they have
components called bearings so if a
bridge can’t move and expand and
contract then stress is built up and we
have problems so that’s just one way to
look at it another way is our example
right from the beginning scoured failure
can we see these tiny movements before
they cause a problem so here’s just one
example from my work and where here’s a
bridge that that we monitored various
different points along the length of the
bridge now in the next slide we’re going
to consider it at that point in the
middle of the bridge we monitored this
over time so you can see tiny tiny
movements over time a couple years
before a certain event in the first year
in 2014 the bridge moved around a little
fairly steady then in 2015 it still
moves around fairly steadily but towards
the end of 2015 was a period of heavy
flooding in the north of England and we
noticed this in November slightly away
from the rest of its friends then again
a little further away and we carry on
and we carry on and then when we get to
December and what happens in December
well that happened in December the
bridge partially collapsed after a
period of severe flooding now this is
just one example and there’s still
plenty of work to be done to develop
this to proper scientific rigor but it’s
a really exciting example of what we
could possibly do with this kind of
technology we’re currently limited by
access to data the resolution the number
of images were able to get at a given
time but the space sector is rapidly
advancing I’m really excited about
working in this field because we have
not yet even started to scratch the
surface with where these opportunities
could go there’s no nursery rhyme you
may know it London Bridge is falling
down well London Bridge is certainly not
falling down but it sure would be nice
to have a pair of eyes in the sky just
to check that it wasn’t right thank you [Applause]