21-07-2012, 04:48 PM
DEMOLITION OF STRUCTURE USING IMPLOSION TECHNOLOGY
DEMOLITION OF STRUCTURE.pdf (Size: 3.45 MB / Downloads: 327)
Introduction
An implosion is an event where something collapses inward, because the
external atmospheric pressure is greater than the internal pressure. For
example, if you pumped the air out of a glass tube, it might implode. When a
building is surrounded by other buildings, it may be necessary to "implode"
the building, that is, make it collapse down into its footprint. You can
demolish a stone wall with a sledgehammer, and it's fairly easy to level a fivestory
building using excavators and wrecking balls. But when you need to
bring down a massive structure, say a 20-story skyscraper you have to haul
out the big guns. Explosive demolition is the preferred method for safely and
efficiently demolishing larger structures.
Methodology
In order to demolish a building safely, blasters must map out each element of
the implosion ahead of time. The first step is to examine architectural
blueprints of the building, if they can be located, to determine how the
building is put together. Next, the blaster crew tours the building (several
times), jotting down notes about the support structure on each floor. Once
they have gathered all the raw data they need, the blasters hammer out a plan
of attack. Drawing from past experiences with similar buildings, they decide
what explosives to use, where to position them in the building and how to time
their detonations. In some cases, the blasters may develop 3 – D computer
model of the structure so they can test out their plan ahead of time in a virtual
world.
The main challenge in bringing a building down is controlling which way it
falls. Ideally, a blasting crew will be able to tumble the building over on one
side, into a parking lot or other open area. This sort of blast is the easiest to
execute, and it is generally the safest way to go. Tipping a building over is
something like felling a tree. To topple the building to the north, the blasters
detonate explosives on the north side of the building first, in the same way you
would chop into a tree from the north side if you wanted it to fall in that
direction. Blasters may also secure steel cables to support columns in the
building, so that they are pulled a certain way as they crumble.
Demolition by Implosion
When all above-mentioned methods of demolition was not found suitable, the
idea of demolition by using implosion technology came to mind as it is being
utilizes worldwide. Though it was not tried over Indian Railway till date.’
Implosion’ is a word which derived from word ‘Implode’ which means, make a
building collapse down on its footprint. The basic idea of implosion is quite
simple, If we remove the support of structure of a building at a certain point,
the structure of a building above that point will collapse. If the upper section is
heavy enough, it will collapse on the lower part of the structure with force to
cause significant damage. The explosives are used in these methods are
such that the whole structure should fall towards its center of its gravity by just
triggering off the explosive in designed manner for demolishing the structures.
The true meaning of implosion of structure is to fall on its footprints, but in
some cases structures are given desired direction of fall during demolition in
order to protect some important existing structures.
Drilling of holes for placement of explosive
The holes were drilled of about 25 mm to 30 mm dia and about 20 to 30 cm
deep depending upon quantity of explosive energy is required to break a
particular support. In this case the building was planned to bring down on
its footprint. We provided 20 holes of 25mm dia & 30 cm in depth central
column .It was reduced to 4 holes of 25mm dia & 20cm deep (4x1) at
columns away from centre.
Quantity of Explosive
The quantity of explosive to be placed depends upon the size of column and
extent up to which it is to be destroyed. Depending on above requirements we
placed 250 gm of explosive in central 24 columns. & 125 gm in outer 16
columns, because it was desired to destroy the central column completely. No
outer column was weakened so that the building collapsed towards its centre
from both side.
Type of explosive & Detonators
There are two types of explosive commonly used for implosion RDX & gelatin.
In this case we used brand name ‘Power Gel ‘ explosive, which is, ammonium
nitrate based explosive which expand at very high speed and applies at a very
high pressure of about 600 T/sq inch. The electronic detonators were used to
ignite the explosive.
Conclusion
It is concluded that this methodology of demolishing building / structure will
prove very useful, economical and quickest in contest of future planned
project in Indian railway i.e. quadrilateral project and freight corridor project,
as during these projects lot of buildings/structures will fall in the alignment of
new lines located nearby existing running lines.