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Overview of Demolition Process
Demolition is an activity in which the construction process is reversed; that is, the structure, or parts of the structure, are disassembled and removed. Sometimes it is misleading to use the word demolition to describe the industry today, since some structures are no longer demolished, but carefully dismantled or deconstructed so that more materials can be reused and recycled.
Our demolition engineers are faced with decision making in the selection of demolition techniques. In practice, the decision is based on the experience, skill, and knowledge of the demolition engineer. Furthermore, there are many elements of the problems, and the interrelationships among the elements are very complicated.
THE DEMOLITION PROCESS
The demolition process can be divided into four main stages: Tendering stage, Pre-demolition stage, Actual demolition stage, and Post-demolition stage.
The demolition process starts when the client makes a decision to demolish a structure. The demolition contractors are then invited to bid for the job.
“Site preparation is the first process in the pre demolition stage. The process may include the erection of security fencing, and the setting-up of welfare facilities (e.g., site office, washing facilities and toilet).
The next process is the decommissioning process. Decommissioning can be defined as a “process whereby an area is brought from its fully operational status to one where all live or charged systems are rendered dead or inert and reduced to the lowest possible hazard level”.
The decommissioning activities include, for example, removal of all asbestos and chemicals (e.g., battery acids and oils), and controlled release of stored energy in strong springs or suspended counterweights. The process followed after decommissioning is soft stripping.
The soft stripping is the removal of non-structural items such as fixtures and fittings, windows, doors, frames, suspended ceilings, and partitions. Some of the product from the soft stripping process can be reused and recycled. Materials, such as wood from windows or door panels, can be reused as building lumber, landscape mulch, pulp chip, and fuel.
The bricks can be cleaned and reused, but this is rarely done. Aluminium, stainless steel panels, and copper are the typical recycled metals. Architectural artefacts, such as sinks, doors, bathtubs, and used building materials, are almost always resold.”
Actual Demolition Stage
The actual demolition starts when the structural elements are demolished.
“The deconstruction technique is defined as the dismantling of a structure, which is usually carried out in the reverse order of construction. It is also known as a topdown technique or, in general terms, the demolition proceeds from the roof to the ground.
The demolition contractors should consider reuse of materials such as bricks, roof tiles, timber, and fixtures and fittings, when using this technique. This technique can be used, for example, as part of renovation or modification work and to prepare the way for deliberate collapse. The elements to be removed should be identified, and the effects of removal on the remaining structure should be fully understood and included in the method statement, with the elements to be removed marked on-site. If instability of any of the remainder might result in a risk to personnel on the site or to other people nearby, sections of the structure should not be removed.
The deconstruction can be done by hand, machines, bursting, or hot cutting. The reuse and recycling process can be done after or concurrently with the structural demolition process. With current technologies such as hydraulic excavators attached with pulverisers, concrete crushing, and screening machines, contractors are able to separate demolition debris. This process can maximise the use of resalable materials and subsequently reduce waste disposal costs. Typical recycled materials are metals and concrete debris. The recycled metals are: scrap iron, rebar (reinforced rods in concrete), aluminium, stainless steel, and copper. Concrete debris is pulverised, and can be used as fill material and sub-base.”
“The final process is the site clearance, in which the site should be left in a safe and secure condition. Any pits, sump, trenches, or voids must be left filled and securely covered, and the site drainage system must be thoroughly cleaned and tested to ensure that it continues to operate.
All contaminants must be left or removed in a manner such that they demonstrate no hazard to health or to the environment. Finally, our planning supervisor will ensure that the Health and Safety File has been compiled and handed to the client upon completion of the work.”
The content of this article is intended to provide a general guide to the subject matter. Contact us on specialist advice about your specific circumstances.