24
MARCH-APRIL 2014
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EXPLOSIVE
DEMOLITION
COURTESY MARCEL SCHROEDER FROM RICHARD LIESEGANG
Record Frankfurt blast
What is believed to be one of the largest
explosive demolition projects ever carried
out in Europe was successfully conducted
on 2 February to bring down the 116 m
(381 ft) tall AfE Tower, formerly occupied by
Frankfurt University, in the centre of that
German city.
According to reports 950 kg (2,090 lb)
of explosive charges were set through the
tower, built in 1972, for the blowdown,
with large filled water tanks positioned
inside the building to help control the
resulting dust. The University moved
out the tower in 2013 and the original
intention was to demolish the tower from
the top down. Local objections to the
length of time required to carry this out,
and the noise and disruption the work
would cause, led to the change of plan.
A 250 m (820 ft) exclusion zone was
established around the tower prior to the
blast. Two new office blocks will be built
once the site is cleared of the resulting
debris.
Cardem decided to proceed by blasting. Due
to the very poor overall condition of the
chimneys, the company decided to perform
a thorough analysis of the structure. This
consisted of running compression tests on the
concrete of each of the 12 sides of each of the
three chimneys, using magnetic resonance
imaging on the concrete reinforcements and
performing scans of the bottom parts of the
chimneys.
This analysis procedure was highly
specialised and extremely innovative in the
approach to a demolition and was carried out
in addition to the usual sight checks of all the
structures. The goal of this in-depth survey
was to ensure that the technical choices made
were the most adapted to the very unusual
context of these structures.
It identified an incredibly high strength
discrepancy on the bottom level all around
the chimneys that generated several potential
risks. The concrete heel might not support
the weight at blast time, concrete hinges were
unfit for supporting the chimneys, the two
concrete layers might have a tendency to split,
different properties of the two layers and
finally three to four layers of rebar were not
properly aligned
CUSTOMISING FOR SUCCESS
Additionally, unstable elements were
inspected and removed by a team of rope
access technicians specifically selected for this
work. This project was a challenging job and
therefore drove us to develop specific methods
and customized systems.
This project was a big success, not because
it went very well, but because Cardem was
able to explain the client how everything was
going to be managed before it happened. Even
more, EDF could be shown exactly how the
blasting was going to be done and the precise
way these chimneys would fall.
The requests of our client were threefold:
a precise, almost surgical procedure that
required four months of studies; a very short
demolition phase, with the real job on the
chimneys started in September for a blast in
October; and finally an overall management
of risk to guarantee safety
Throughout the project, demolition
operations were shown to the client before
being performed on site. The client was
constantly involved and was confident
because, step by step, a virtual overview of
what was going to happen next and why as
always available. The project was delivered on
time and to budget, and most of all, with no
lost time incidents.
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The final cleared site after the chimneys fell precisely as planned
