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December, 1999 DEMOLITION is one area India has never bothered to concentrate upon. Ours being a developing country, emphasis has rather been on development. We develop cold feet when it comes to demolishing some structure. There exist innumerable old and unsafe buildings; narrow, half-a-lane bridges that need to be demolished to give way to new multistoreyed buildings; wide and safe flyovers. Traffic is increasing day by day and business is on the rise thus demanding more and more buildings, offices, commercial buildings, dwelling units and a well-connected and capable road-transport-network. All this is possible only if the old and outlived structures are removed and land is freed for the new ones to come up. In India, demolition is avoided as if it is something inauspicious, involving wasteful expenditure. Another factor is our crude method of demolition. If we are asked to demolish an old bridge or a building, we put a large labour force armed with chisels and hammers on it. Otherwise we try to ram a bull-dozer into the structure. At the most we deploy some pneumatic jack-hammers to dismantle the RCC or brick-work. There exit no planned methods to execute “demolition”. Now is the time that India develops demolition technology suitable to Indian conditions. For this, the structures are to be categorised and requirements are to be defined. A blind adoption of the techniques being used in foreign countries may not be conducive to Indian layout. Indian structures On a broader scale and from demolition point of view, the Indian structures can be divided into following categories: 1. Tall chimneys of power plants and large sized natural draught cooling towers. 2. Multistoreyed buildings. 3. Heavily reinforced bridges and buildings. 4. Ordinary buildings, houses, brick-structures etc. Requirements Thinking of the requirements that the demolition technology should fulfil, the following shall form an ideal list: 1. Quicker demolition. 2. Quieter demolition. 3. Cheaper demolition. 4. Environment-friendly demolition. 5. Demolition causing least disturbance in the neighbourhood. Therefore, whenever a structure is to be demolished, it must be seen that the method adopted is such that it takes minimum time, produces least level noise, causes no pollution beyond permissible limits, does not disturb the activity or living in the neighbourhood and proves cheaper also. In foreign countries, regulations exist to control dust and noise pollution during demolition. Such regulations can be devised for our country also even though most of the demolitions will fall within the ambit of government departments only. Physical survey It is essential to survey the surroundings of the structure to be demolished. The surroundings will decide whether a structure is to be toppled or made to collapse or shattered or imploded or exploded. The position of the water-supply lines, telephone cables and electricity wires is also to be checked. It has to be ensured that the supplies to the adjacent buildings are not disturbed. Whenever explosion-demolition technology is to be used, it is to be seen that the computers and the equipment installed in the nearby buildings are not affected by the vibrations produced by the explosions. If a demolition involves rise of clouds of dust, the ducts of AC systems in the adjacent buildings are to be sealed against entry of dust in them. Overall approach has to be cause least disturbance to the surroundings. The construction drawings of the structure to be dismantled will not be available as it may be over 40 to 50 years since the time that structure was built. Therefore core tests may be done to have an idea of the concrete strength or density of reinforcement. The position of the expansion joints in the building should also be assessed as it will help in planning the demolition of the building. Technology abroad Explosive demolition technology has become most popular in foreign countries. High-rise chimneys and massive cooling towers are made to collapse through telescopic technique by placing explosives in such a manner that an almost vertical collapse occurs. Under this technique, large compressive stresses are produced at the base of the structure and it descends in a continuous manner like a house of cards. While the explosives cause the initial collapse, further fragmentation is caused by gravity only. Often such demolitions provide a spectacular show making people wonder at the advance of technology. Technically, this is just a game of following a laid set of guidelines and an expert supervision. Wherever environmental regulations impose restrictions over use of explosives, chemical techniques are being applied. These techniques also are highly effective. Alloy steel cartridges filled with liquid carbon dioxide and some chemical igniting agent are fixed in position and then detonated from a safe distance. Expanding carbon dioxide gas breaks up steel cartridge and attacks the surrounding material with a cold heaving force. This technique is capable of breaking very hard materials. Water bursting and water jetting are other techniques being used. Special methods are being devised to dismantle pre-stressed concrete and post-tensioned concrete structures. Lessons for India Indian conditions are not fully ripe to adopt explosive demolition technology. Dense population, haphazard growth, non-existence of any byelaws or regulations and our casual approach makes use of explosives a risky affair for us. The complex and dangerous business of use of explosives needs a very strict set of guidelines to be followed in an explicit manner, an expert supervision and a comprehensive planning exercise to determine the sequence of removal of components of the structure and the placement of the charges. Minutest details are to be worked out. For example, the rough end of a steel bar exposed while making holes can cut the detonating cord or detonator lead wires. A record of the vibrations and airblasts produced has to be kept and instruments capable of making these measurements should be installed. Private companies who promise to develop foolproof methodology for explosive demolition should be extended full cooperation and assistance by the Government. Hydro-demolition is another area India should concentrate upon. Heavyduty hydraulic hammers of 30 to 50 tonne class develop by Krupp industries can operate at 250 to 450 blows per minute and can work underwater also. Other leading companies of the world such as Labounty of USA whose universal processor can rotate at 360 degrees and can demolish concrete as well as steel by fixing alternative jaws, Brokk of Sweden, which is known for noiseless concrete demolition, Conjet of Sweden that can cut concrete and asphalt by water-jet system at twice the speed of sound, NPK of Japan that provides world class hydraulic rammers and Atlas Copco of Sweden which is a master of rock-drilling technology should be allured to collaborate with Indian firms till the time a switch-over of technology takes place.
While the telescopic collapse triggered by explosion technology is most suitable for tall chimneys and cooling towers, hydro-demolition suits multistoreyed buildings and the densely reinforced concrete structures. Ordinary buildings, houses and brick-structures can be demolished by hydraulic hammers, jack rammers, impact breakers or ordinary splitters. Final choice of the technique to be adopted however, depends upon the actual site conditions. Day by day, re-development of walled cities, better utilisation of land and rapid industrial advancement is demanding for development of cost-effective, environment-friendly, quick and quiet demolition technology. It is time we too this aspect too within our stride during our relentless march for progress.
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