demolition of structure using implosion technology
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PROJECT REPORT
ON
DEMOLISION OF STRUCTURES USING IMPLOSION TECHNOLOGY
SESSION NO 514 INTEGRATED COURSE IRICEN PUNE
GUIDED BY: SRI. A.K.RAI
(PROFESSOR - WORKS) IRICEN PUNE
PRESENTED BY
A. K. ARYA, ADEN (S/E) / PL A.K.SHARMA, ADEN (S) / BRC
ARVIND KUMAR, Mgr / IRCON N.K.SHARMA, ADEN (G) / BKN
INDEX Sl. Description Page no. 1. Introduction 1
2. Methodology 1 – 3
3. Demolition of structure using implosion
Technology: A case study 3 – 8
4. Explosive details 9 – 13
5. Conclusion 13
ACKNOWLEDGEMENT
We are very much grateful to SHRI SHIV KUMAR
Director/IRICEN, SHRI A. K. RAI, Course Director
and Professor Works for their valuable guidance and
consistent encouragement in preparing the project. Finally, we thanks to all faculty members and IRICEN staff for offering
their valuable assistance and providing a conducive atmosphere to compile
these reports in presentable form.
DEMOLITION OF STRUCTURE USING
IMPLOSION TECHNOLOGY 1.0 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 five-
story 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.
The basic idea of explosive demolition is quite simple: If you remove the
support structure of a building at a certain point, the section of the building
above that point will fall down on the part of the building below that point. If
this upper section is heavy enough, it will collide with the lower part with
sufficient force to cause significant damage. The explosives are just the
trigger for the demolition. It's gravity that brings the building down.
Demolition blasters load explosives on several different levels of the building
so that the building structure falls down on itself at multiple points. When
everything is planned and executed correctly, the total damage of the
explosives and falling building material is sufficient to collapse the structure
entirely, so clean-up crews are left with only a pile of rubble.
2.0 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.
Sometimes, though, a building is surrounded by structures that must be
preserved. In this case, the blasters proceed with a true implosion,
demolishing the building so that it collapses straight down into its own
footprint (the total area at the base of the building). This feat requires such
skill that only a handful of demolition companies in the world will attempt it.
Blasters approach each project a little differently, but the basic idea is to think
of the building as a collection of separate towers. The blasters set the
explosives so that each "tower" falls toward the center of the building, in
roughly the same way that they would set the explosives to topple a single
structure to the side. When the explosives are detonated in the right order, the
toppling towers crash against each other, and all of the rubble collects at the
center of the building. Another option is to detonate the columns at the center
of the building before the other columns so that the building's sides fall inward
According to Brent Blanchard, an implosion expert with the demolition-
consulting firm Protec documentation services virtually every building in the
world is unique. And for any given building, there are any number of ways a
blasting crew might bring it down. Blanchard notes the demolition of the
Hayes Homes, a 10-building housing project in Newark, New Jersey, which
was demolished in three separate phases over the course of three years. "A
different blasting firm performed each phase," Blanchard says, "and although
all of the buildings were identical, each blaster chose a slightly different type
of explosive and loaded varying numbers of support columns. They even
brought the buildings down in different mathematical sequences, with varying
amounts of time factored in between each building's collapse."
Generally speaking, blasters will explode the major support columns on the
lower floors first and then a few upper stories. In a 20-story building, for
example, the blasters might blow the columns on the first and second floor, as
well as the 12th and 15th floors. In most cases, blowing the support structures
on the lower floors is sufficient for collapsing the building, but loading columns
on upper floors helps break the building material into smaller pieces as it falls.
This makes for easier clean-up following the blast.
Once the blasters have figured out how to set up an implosion, it's time to
prepare the building. In the next section, we'll find out what's involved in pre-
detonation prepping and see how blasters rig the explosives for a precisely
timed demolition.
3.0 Demolition of structure using Implosion Technology: A case study
Introduction An structure which is made by any material is to be demolished after it’s
designed age is completed in order to reutilised the valuable land. Demolition
was also necessary to remove danger of falling. In western railway, Mumbai
division, there was a G+3 storied building numbered as 25/T. It was built in
1924, constructed by BB & CI railway as a first cement concrete residential
structure in Mumbai. It was having 80 Nos. (4×20) type I Quarter with total
land area about 430 Sq. m. The total height was 13.20 m. above rail level.
The structure completed its designed life and existing condition of building
was so deteriorated that there was no option but to demolition the same for
safety of running trains and adjoining residents.
Options for Demolition (Conventional Methods) As usual there are two methods for demolition. One by manually and other by
mechanical means such as using JCB, Poclains, etc. While planning for the
method to be adopted a lot of discussion was held and it was concluded that
neither of above method is suitable due to existing constraints around chawl
No. 25/T. These were as under.
1. There were four running lines just adjoining to structure in east side, the
face of building was just 4.55m away from track centre.
2. There was a OHE Mast containing portal for five numbers OHE live
conductors at a distance of 5.80 m. from face of building towards north side.
3. There was stone masonry boundary wall at a distance of 2.80 m. from
face of building.
4. In addition to above as described railway’s assets, there was a 40 storied
structure about 100 m. away from building to be demolished and one diamond
factory exists in the east side having exterior glazed building.
Due to above said constraints, manual method was not suitable as it
was going to take more time and structure was very near to running track
which requires continuous track protection / traffic block. Which would have
resulted longer disruptions to running traffic .The mechanical method was not
suitable, as there was no space to bring heavy machineries near the structure
and to work at a height of 13.50 m.
In the context of this project it is advisable and worthy to note that railway
context, this method of demolishing would be proved very suitable and useful,
most of railway assets i.e. building / structure located nearby running track
and in metro cities congested area which already passed their designed life.
Also in the view of Golden Quadrilateral and Freight corridors projects lots of
structures will be dismantled during execution of these projects.
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.
The advantages of implosion technology method over conventional methods are as under. 1.It is less expensive. 2.There are no ground vibrations 3.ThisMethod is quickest. 4. Suitable for multi-storeyed structures / high piers, cabins, distressed piers etc.
Important Aspect of Implosion Technology
Following are important aspects of Implosion
Analysis of Existing structure & locating weak points
The approximate strength of left on R.C.C / PSC member worked out by
taking the core of concrete, In order to decide quantity /location of explosive to
be provided. In our case the structure was very much dilapidated and unsafe,
there was no need to carry out such tests as weakening of strength of
structure was done by making the vertical columns from adjoining partition
wall, which were of RCC
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
Holes drilled in columns for placement 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.
PLACEMENT OF EXPLOSIVES – CROSS SECTIONAL VIEW
Test Blast
Before carrying out the actual blasting;
We done a test blast, in ordered to ascertain the efficiency of explosive &
detonators and also to develop a level of confidence as this was a specialized
work and executed 1st time on in Indian railway.
BEFORE AFTER
Wrapping of holes
The wrapping of holes is done to ensure that due to explosion of charges the
debris does not fly in air. For this purpose, the holes were covered with gunny
bags and iron net after placement of explosive and detonators.
Ground floor
Ballasting
Ballasting of Charges / Explosives work are carried out in a controlled manner
such that there will be a time gap of 1/100 second between two successive
blasts. The trigger of charges is done in such a control manner so that the
noise pollution and air pollution should be minimum. The central column is first
triggered and then blast proceed towards outside to produce three way action
and hence results the fall of existing structure on its footprint.
Falling of structure
Once central support/column will be destroyed and adjoining columns will be
weakened, due to its gravity the entire mass will come down on its footprints.
In this case after blasting within few seconds the entire structure of (g+3)
storied came down on its footprint without damaging any adjoining asset.
4.0 Explosive
Explosive, substance that undergoes decomposition or combustion with great
rapidity, evolving much heat and producing a large volume of gas. The
reaction products fill a much greater volume than that occupied by the original
material and exert an enormous pressure, which can be used for blasting and
for propelling.
Classification of Explosives
Chemical explosives can be classified as low or high explosives. Low (or
deflagrating) explosives are used primarily for propelling; they are mixtures of
readily combustible substances (e.g., gunpowder) that when set off (by
ignition) undergo rapid combustion. High (or detonating) explosives (e.g.,
TNT) are used mainly for shattering; they are unstable molecules that can
undergo explosive decomposition without any external source of oxygen and
in which the chemical reaction produces rapid shock waves. Important
explosives include trinitrotoluene (TNT), dynamite, nitrocellulose, nitroglycerin,
and picric acid. Cyclonite (RDX) was an important explosive in World War II.
Ammonium nitrate is of major importance in blasting.
Applications of Explosives (Detonators and Dynamite) In the last section, we saw how blasters plan out a building implosion. Once
they have a clear idea of how the structure should fall, it's time to prepare the
building. The first step in preparation, which often begins before the blasters
have actually surveyed the site, is to clear any debris out of the building. Next,
construction crews, or, more accurately, destruction crews, begin taking out
non-load-bearing walls within the building. This makes for a cleaner break at
each floor: If these walls were left intact, they would stiffen the building,
hindering its collapse. Destruction crews may also weaken the supporting
columns with sledgehammers or steel-cutters, so that they give way more
easily.
Next, blasters can start loading the columns with explosives. Blasters use
different explosives for different materials, and determine the amount of
explosives needed based on the thickness of the material. For concrete
columns, blasters use traditional dynamite or a similar explosive material.
Dynamite is just absorbent stuffing soaked in a highly combustible chemical or
mixture of chemicals. When the chemical is ignited, it burns quickly, producing
a large volume of hot gas in a short amount of time. This gas expands rapidly,
applying immense outward pressure (up to 600 tons per square inch) on
whatever is around it. Blasters cram this explosive material into narrow
boreholes drilled in the concrete columns. When the explosives are ignited,
the sudden outward pressure sends a powerful shock wave busting through
the column at supersonic speed, shattering the concrete into tiny chunks.
Demolishing steel columns is a bit more difficult, as the dense material is
much stronger. For buildings with a steel support structure, blasters typically
use the specialized explosive material cyclotrimethylene trinitramine, called
RDX for short. RDX-based explosive compounds expand at a very high rate of
speed, up to 27,000 feet per second (8,230 meters per second). Instead of
disintegrating the entire column, the concentrated, high-velocity pressure
slices right through the steel, splitting it in half. Additionally, blasters may
ignite dynamite on one side of the column to push it over in a particular
direction.
To ignite both RDX and dynamite, you must apply a severe shock. In building
demolition, blasters accomplish this with a blasting cap, a small amount of
explosive material (called the primer charge) connected to some sort of fuse.
The traditional fuse design is a long cord with explosive material inside. When
you ignite one end of the cord, the explosive material inside it burns at a
steady pace, and the flame travels down the cord to the detonator on the
other end. When it reaches this point, it sets off the primary charge.
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These days, blasters often use an electrical detonator instead of a traditional
fuse. An electrical detonator fuse, called a lead line, is just a long length of
electrical wire. At the detonator end, the wire is surrounded by a layer of
explosive material. This detonator is attached directly to the primer charge
affixed to the main explosives. When you send current through the wire (by
hooking it up to a battery, for example), electrical resistance causes the wire
to heat up. This heat ignites the flammable substance on the detonator end,
which in turn sets off the primer charge, which triggers the main explosives.
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To control the explosion sequence, blasters configure the blast caps with
simple delay mechanisms, sections of slow-burning material positioned
between the fuse and the primer charge. By using a longer or shorter length of
delay material, the blasters can adjust how long it takes each explosive to go
off. The length of the fuse itself is also a factor, since it will take much longer
for the charge to move down a longer fuse than a shorter one. Using these
timing devices, the blasters precisely dictate the order of the explosions.
Blasters determine how much explosive material to use based largely on their
own experience and the information provided by the architects and engineers
who originally built the building. But most of the time, they won't rely on this
data alone. To make sure they don't overload or under-load the support
structure, the blasters perform a test blast on a few of the columns, which they
wrap in a shield for safety. The blasters try out varying degrees of explosive
material, and based on the effectiveness of each explosion, they determine
the minimum explosive charge needed to demolish the columns. By using
only the necessary amount of explosive material, the blasters minimize flying
debris, reducing the likelihood of damaging nearby structures.
To further reduce flying debris, blasters may wrap chain-link fencing and
geotextile fabric around each column. The fence keeps the large chunks of
concrete from flying out, and the fabric catches most of the smaller bits.
Blasters may also wrap fabric around the outside of each floor that is rigged
with explosives. This acts as an extra net to contain any exploding concrete
that tears through the material around each individual column. Structures
surrounding the building may also be covered to protect them from flying
debris and the pressure of the explosions.
When everything is set up, it's time to get the show underway. In the next
section, we'll find out what final steps the blasters must take to prepare for the
implosion, and we'll look at the implosion itself. We'll also find out what can go
wrong in explosive demolition and see how blasters evaluate the project once
the smoke has cleared.
In the last couple of sections, we looked at everything blasters do to prepare a
building for implosion. In addition to these measures, the blasters must
prepare the people in the area for the blast, assuring local authorities and
neighbouring businesses that the demolition won't seriously damage nearby
structures. The best way blasters can calm down anxious authorities is by
demonstrating the firm's success with previous implosions.
c uses portable field seismographs to measure ground vibrations and air-
blasts during an implosion. Brent Blanchard, an operations manager for the
company, says that they also inspect surrounding structures prior to the
implosion, so that they can help assess any damage claims following the
blast. Additionally, Protec's staffs videotape the blast from multiple angles so
that there is a record of what actually happened. Using data collected from
previous blasts, the company's engineers can predict ahead of time what level
of vibration a particular implosion may cause.
Once the structure has been pre-weakened and all the explosives have been
loaded, it's time to make the final preparations. Blasters perform a last check
of the explosives, and make sure the building and the area surrounding it are
completely clear. Surprisingly, implosion enthusiasts sometimes try to sneak
past barriers for a closer view of the blast, despite the obvious risks. With the
level of destruction involved, it is imperative that all spectators be a good
distance away. Blasters calculate this safety perimeter based on the size of
the building and the amount of explosives used.
On occasion, blasters have misjudged the range of flying debris, and
onlookers have been seriously injured. Blasters might also overestimate the
amount of explosive power needed to break up the structure, and so produce
a more powerful blast than is necessary. If they underestimate what explosive
power is needed, or some of the explosives fail to ignite, the structure may not
be completely demolished. In this case, the demolition crew brings in
excavators and wrecking balls to finish the job. All of these mishaps are
extremely rare in the demolition industry. Safety is a blaster's number-one
concern, and, for the most part, they can predict very well what will happen in
an implosion.
Once the area is clear, the blasters retreat to the detonator controls and begin
the countdown. The blasters may sound a siren at the 10-minute, five-minute
and one-minute mark, to let everyone know when the building will be coming
down. If they are using an electrical detonator, the blasters have a detonator
controller with two buttons, one labelled "charge" and one labelled "fire."
Toward the end of the countdown, a blaster presses and holds the "charge"
button until an indicator light comes on. This builds up the intense electrical
charge needed to activate the detonators (this is similar to charging a camera
flash to build the necessary electrical energy to illuminate a scene). After the
detonator-control machine is charged, and the countdown is completed, the
blaster presses the "fire" button (while still holding down the charge button),
releasing the charge into the wires so it can set off the blasting caps.
Typically, the actual implosion only takes a few seconds. To many onlookers,
the speed of destruction is the most incredible aspect of an implosion. How
can a building that took months and months to build, and stood up to the
elements for a hundred years or more, collapse into a pile of rubble as if it
were a sand castle?
Following the blast, a cloud of dust billows out around the wreckage,
enveloping nearby spectators. This cloud can be a nuisance to anyone living
near the blast site, but blasters point out that it is actually less intrusive than
the dust kicked up by non-explosive demolition. When workers take down
buildings using sledgehammers and wrecking balls, the demolition process
may take weeks or months. In this time, a significant amount of dust is being
kicked up into the air every day. When the building is levelled in one moment,
on the other hand, all the dust is concentrated in one cloud, which lingers for a
relatively short period of time. Nearby residents with allergies can leave the
area for that one-day and avoid the dust entirely.
After the cloud has cleared, the blasters survey the scene and review the
tapes to see if everything went according to plan. At this stage, it is crucial to
confirm that all of the explosives were detonated and to remove any
explosives that did not go off. If a demolition consulting crew was on hand, the
blasters review their vibration and air blast data as well. Most of the time,
experienced blasters bring buildings down exactly as planned. Damage to
nearby structures, even ones immediately adjacent to the blast site, is usually
limited to a few broken windows. And if something doesn't work out quite right,
the blasters log it in their mental catalogue and make sure it doesn't happen
on the next job. In this way, job-by-job, the science and art of implosion
continues to evolve.
5.0 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.
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