Safety in Demolition and Underpinning Work · SAFETY IN DEMOLITION AND UNDERPINNING WORK National Safety Council, India SAFETY IN DEMOLITION & UNDERPINNING WORK 1. DEMOLITION It is

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SAFETY IN DEMOLITION AND

UNDERPINNING WORK

National Safety Council, India

SAFETY IN DEMOLITION & UNDERPINNING WORK 1. DEMOLITION It is general experience that far less regard and consideration is given to the demolition or dismantling of structures then to erection, construction and maintenance; although the problems, hazards and uncertainties can be much greater as the demolition is frequently carried out by the unskilled workers. The design engineers have the responsibility not only for the safe design and construction but also for the safe demolition of the structure at the end of its designed life. Necessary measures needed for a safe and smooth demolition can be incorporated at the design / construction stage.

I. Legal requirements for Demolition

• The Building And Other Construction Workers (Regulation Of Employment And

Conditions Of Service) Act, 1996 And BOCW Central Chapter XII Rules ,1998

• The Hazardous Wastes (Management, Handling and Transboundry Movement)

Rules, 2008, (amended 2010)

• The Noise Pollution (Regulation & Control ) Rules, 2000 (amended 2010)

• The Environmental (Protection) Act, 1986 (amended 1991)

• The Environment (Protection) Rules, 1986 (amended 2010)

• The Municipal Solid Waste (Management & Handling) Rules, 2000.

• IS CODE:IS 4130:1991 Demolition of buildings - Code of Safety .

II. Common Safety Hazards and Environmental Aspects in Demolition

• Unintentional collapse of structure or part of it.

• People and objects falling from heights.

• Striking overhead or underground services.

• Manual handling activities associated with demolition and material movement.

• Generation of Demolition debris.

• Hazardous substances in debris.

• Dust emission.

• Generation of noise.

• Effect on micro- climate.

• Segregation of the generated debris due to demolition activity is required

between hazardous and non-hazardous debris.

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III. Methodology for Safe Demolition

The methods of demolition include hand or manual demolition; mechanical demolition by pusher arm, demolition ball and wire rope pulling; explosives; demolition by hydraulic busters and the thermic lance. These methods of demolition are suitable for particular types of buildings and structures such as houses, large buildings, bridges, arches, independent chimneys, steel and concrete structures, spires, pylons and masts, petroleum tanks etc. Demolition process in all types of structure is not same and all debris and waste generated during demolition shouldn’t be used for landfilling.

IV. Actions to be taken before any demolition work is taken up:

• It should be preceded by a site survey which should be comprehensive and

cover the position of screens, scaffolds etc.

• Protection of the public shall be ensured and also methods to ensure the

stability of surrounding buildings/structures from the danger of collapse due to

withdrawal of support or undermining of the foundations shall be paid attention.

• The electric power to all services within the structures to be demolished should

be shut off or discontinued at outside the building.

• All gas, water and steam service lines should be shut off or otherwise controlled

outside the structure to the demolished.

• The structure to be demolished should be adequately fenced and cordoned off

and suitable board shall be prominently displayed to warn the public.

• Measures for dust suppression / control shall be in place.

V. Safety measures in demolition of the buildings:

Demolition operations should begin with by removing glass in doors and windows, loose objects and projecting parts. Workers should not be deployed at different levels unless adequate precautions are taken to ensure safety of those deployed levels. Demolition work should begin at the top of the structure and process downwards. Masonry concrete and other dismantled materials should not be allowed to accumulate in quantities which may endanger the stability of any floor or structural support. Part of the structures, where necessary should be adequately shored, braced or otherwise supported. If the structure is to be demolished by explosives, all safety measures pertaining to explosives such as transport, storage, handling, loading firing etc. should be strictly adhered to. Foundation walls serving as retaining walls to support of adjoining structures should not be demolished until the adjoining structure have been under pinned or braced or earth supported by sheet pilling.

Stairs with hand railing should be kept in place as long as practicable to provide access and egress. If the work of demolition is continued at height, all

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passageways, stairs and other parts of the structure where the workers have to pass and work, should be adequately lit. Workers should strictly wear safety harness / belts, safety helmets, hand glove and goggles.

If the demolition is carried out by machines such as power shovels, bulldozers etc. the safety measures relevant to operation and use of such machines should be adhered to. If swinging weight such as ball is used for demolition, a safety zone having a width of at least 1.50 times the height of the building or structure should be maintained.

Scaffolds used for demolition operations should be independent of the structure to be demolished. If ladders are used for demolition, only travelling type mechanical ladders should be used, except that ordinary ladders may be used as means of access to the scaffolds. The hoists or chutes, whenever it is practicable, should be used to lower the materials. Materials chutes should have a gate at the bottom with suitable means for regulating the flow of materials. The safest way to transport the debris generated at different levels in demolition is by material hoist or chutes.

Whenever the condition demands, suitable catch platforms (at least 1.50 M. wide) should be provided along the outside of the exterior walls so as to prevent danger from falling objects. The catch platforms should be moved downward as the level of demolition operation gets lowered. The catch platforms should be inclined such that the outer edge is higher than the inner edge for arresting fall of material during demolition.

VI. Safety measures in demolition of structural steelworks:

The steel structures should be demolished from top tier by tier. There should be a definite plan and sequence of removing the various members of the steel structure. All precautions should be taken to prevent danger from any sudden twist, spring or collapse of steel parts / work when it is cut or released. Removed parts should be carefully lowered and not to be dropped from a height. Safety precautions of gas cutting of should be adhered to.

VII. Safety measures in demolition of tall chimneys, minars, pylons etc.

Tall chimneys, minars, pylons, etc., should not be demolished by overturning or blasting unless a protected area of an adequate dimension can be established in which the chimney or the structure can fall safely. If the demolition of the tall structure is resorted to by blasting with explosives, the services of the specialist engineer should be requisitioned for the pattern of drilling, the size of the holes to drilled, the charge of the explosives & the entire sequence of the firing of the explosives etc. The entire operation should be under supervision and control of the competent person. The whole area shall remain out of bounds for public.

VIII. Safety measures in demolition of Industrial Structures:

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Required safety measures, in addition to some of the relevant safety measures stated herein before, should be observed in removing heavy and bulky machinery, plant and equipment. For example, If the industrial structure such as a nuclear power station is to be demolished, the services of the specialist expert in the field of radio-activity and radiation should be requisitioned for the operation of the demolition of the structures which has radiation hazards. The entire operation of the demolition is to be planned by the specialist engineer, in consultation with the demolition engineer. Segregate and dispose hazardous waste separately as per applicable law.

Worker getting struck by excavator during Demolition Activity

2. UNDERPINNING In construction, underpinning is the process of strengthening and stabilizing the foundation of an existing building or other structure. Underpinning may be necessary for a variety of reasons:

• The original foundation is simply not strong or stable enough.

• The intended usage of structure has changed.

• The properties of the soil supporting the foundation may have changed (possibly through subsidence) or were mischaracterized during planning.

• The construction of nearby structures necessitates the excavation of soil supporting existing foundations.

• It is more economical, due to land price or otherwise, to work on the present structure's foundation than to build a new one.

• The existing foundations of the building have moved – this is caused by poor soil or changes to the soil conditions (e.g. subsidence has occurred).

• There has been a decision to add another storey to the building, either above or below ground level, and the depth of the existing foundations is inadequate to support the modified building or load (weight) of it.

Underpinning is accomplished by extending the foundation in depth or in breadth so that it either rests on more supportive soil stratum or distributes its load across a greater area. Use of micro piles and jet grouting are common methods in underpinning. An alternative to underpinning is the strengthening of the soil by the

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introduction of a grout. All these processes are generally expensive and elaborate. Underpinning work requires very careful planning and execution. An initial step, before substantial commencement of the work, will generally be to dig a trial hole next to the existing footings/foundation to make an assessment of the conditions by an expert engineer.

It is a messy, noisy and traumatic operation for buildings and their occupants alike. Unless sophisticated and expensive jacking systems are incorporated, the underpinning will almost inevitably promote some additional subsidence as the works settle in. If a structure is partially underpinned, then future damage may recur as the rest of the non-underpinned structure continues settling. For these reasons, underpinning should be avoided if at all possible.

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Fig. 1 Underpinning the foundations of a railway bridge. A completed concrete pad underpinning can be seen at the bottom right. IX. Safety measures – Underpinning

Most types of underpinning involve digging holes under buildings in confined spaces. The existing structure is expected to defy gravity and temporarily arch over the excavation. Collapses can occur and the following related risks must be identified and managed accordingly -

• Investigate services before starting excavation

• Always do excavation at angle greater than angle of response of soil

• Check that underpinning pits cannot get flooded or be gassed

• Strengthen superstructure before digging

• Check that walls above are strong enough to support themselves over pits

• Support sides of excavations

• Ensure that workers can escape from pits easily

• Use threaded couplers instead of dowel bars to connect reinforcement rods between sections of shallow mass concrete underpinning

• Ensure strengthening of nearby surrounding structures

• Provide all required PPE’s (Safety Harness, Safety Helmet, Safety Shoes,

Mask, Safety Goggles, Safety Jacket

• Ensure safe access and ventilation to pits

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