RAILWAY STRUCTURES MAINTENANCE
No.3 In Series of Articles - written by
Dave Haynes
First published in FMRC Turntable Newsletter No
149 September/October 1998
also in NWMRCA The Signalmen newsletter
Vol 2 issue 11 Autumn 1999
Bridge No 5a, Caledonian Line -
Monitoring Pier Movement
This bridge carries the Up and Down Goods lines over the River
Eden less than 1 mile north of Carlisle Station and immediately
before entering Kingmoor Depot. It was constructed circa 1944 and
consists of nine spans. The visible construction for each pier
consists of two rows of five reinforced concrete columns which
terminate at soffit level with a reinforced concrete crosshead
carrying pre-cast concrete tee-beams. The foundations are either
piles and caps or in the case of the piers 1 to 5, ' bents' ,
that is piles continued directly into columns. The individual
columns within each pier group rake at various random angles up
to approximately 5 degrees from vertical.
| Following bridge
examination reports which suggested that there may be
movement in the columns of two piers, I set up a system
to monitor vertical and horizontal movement in these
piers. The conventional systems of monitoring employed
are Avonguard tags, plumbing and other taped systems,
none of which measure all three dimensions together.
Therefore I used an electronic
total station, fixing reflective targets on the piers
at high and low levels as points of reference for
detection of movement, tied in with a fixed traverse of three triangulation
stations around Pier 2, seen on the left hand side of
Plate 1. Targets in prone locations were removable,
relying on only a metal stud fixed to the concrete as a
means of location, these can be seen as black plates
midway down the piers on Plate2.
Upon collecting the data, I was able to record any
movement in X, Y or Z direction and ultimately, look for
trends to indicate movement in one direction.
Incidentally, the bridge didn't show signs of falling
over but it did show movement with the seasons, as if it
breathed in for the winter and out again in summer!
|
Plate 1 - Bridge 5A Caledonian
Line, East Elevation Of Piers 2 & 3
Plate 2 - Bridge 5A Caledonian
Line, South Elevation Of Pier 3
|
Notes
Avonguard tag -
these consists of two perspex sheets 100 x 100mm each with
graduated lines marked on. The tag is glued over a fracture and
movement in the fracture can be measured to 0.5mm. 
Plumbing - measuring
the offset from a vertical plumb line at frequent intervals and
distances between points (' stations' ) is known and the
3-dimensional location of each point is known, the traverse can
be used as a reference to come back to at subsequent visits.
Electronic total
station - these are 'theodolites with wings',
allowing the geometry of a site to be determined in terms of
angles and distances, all of this being done with a precision
optical telescope and allied equipment.
Traverse - for example
a triangle - if angles and distances between points ('stations')
is known and the 3-dimensional location of each point is known,
the traverse can be used as a reference to come back to at
subsequent visits, thus making it possible to see if the shape of
the traverse has changed, indicating movement.
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Copyright D Haynes
Last revised: July 19, 2000.
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