SAFETY MEASURES IN CONSTRUCTION FOUNDATION.

Foundation work often involves massive operations in earthwork such as excavation

or digging large holes in the ground, or where the face of the earth, rock, sand, soil or

other materials are removed.

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Typical examples are:

▪ a trench, ditch, shaft well, tunnel, pier hole, cutting, caisson or cofferdam

▪ a hole drilled into the earth

Cave-ins are the most feared hazard in earthworks like excavation and trench work.

But other potentially fatal hazards exist, including asphyxiation due to the lack of

oxygen in a confined space, inhalation of toxic fumes, drowning, etc. Electrocution or

explosions can occur when workers are in contact with exposed underground utilities.

Caisson

For many years, hand-dug caissons had gone through a disturbing history of high 

accident rate and health hazards. The Building Authority in 1995 banned the use of

hand-dug caissons mainly to minimize workers from:

▪ being struck by an object falling into the excavation

▪ being trapped by the collapse of an excavation (all depths)

▪ falling into the excavation

▪ asphyxiations, inhaling, or otherwise being exposed to, carbon monoxide or

other impurities in the air in the vicinity of the excavation

▪ drowning/burying when overcome by sudden in-flush of water

▪ other hazards including noise, silica dust, explosive or flammable gases, such

as methaneExemption may be granted only if an architect or structural engineer can demonstrate

to the satisfaction of the Building Authority that the following circumstances exist:

▪ the depth of the hand-dug caisson does not exceed 3 meters and the

diameter of the inscribed circle of the hand-dug caisson is not less than 1.5

meters; or

▪ for the site concerned:

􀃠 the use of a hand-dug caisson is the only practical construction method; or

􀃠 there is no other safe engineering alternative.

Examples of these are: narrow or steep sloping sites where difficult access or

insufficient working space makes it not possible or not safe to use machine tools.

In these exceptional circumstances, the authorized person/registered structural

the engineer must specify stringent safety requirements in the method statement for the

building works and ensure that the registered contractor is fully aware of and complies

with all safety requirements. In this respect, the provisions of the Construction Site

(Safety) Regulations administered by the Commissioner for Labour should be

observed.

In all caisson operations, including complex foundation work, a risk assessment

should always be conducted in the early planning stages.

Risk assessment 

▪ Assess the risks that may result because of the

hazards

▪ Decide on control measures to prevent or minimize

the level of the risks

▪ Implement the control measures

▪ Monitor and review the effectiveness of the control

measures 

Person being trapped by the collapse of an excavation (all depths)

▪ do as much work as possible from outside the

excavation

▪ backfill excavation as soon as possible

▪ batter, bench or shore sides of excavation

▪ place excavated materials, equipment and other materials at a distance from the edge of the

excavation so that the force exerted on the edge of the excavation does not lead to the collapse of the

excavation

▪ limit the approach of vehicles and plant by erecting a barrier, such as a wheel buffer

 Person being trapped by the collapse of a trench more than 1.5 m deep

▪ shore all sides of the trench; or

▪ bench all sides of the trench; or

▪ batter all sides of the trench; or

▪ obtain written approval from a geotechnical engineer that all sides of the trench are safe from

collapse; or

▪ use a combination of the above measures 

Person being struck by an object falling into the excavation

▪ do not lift or suspend loads over any person working in the excavation

▪ use excavators and cranes with controlled descent valves on the hydraulics fitted to the boom or

dipper arm to prevent the boom or load from falling onto the workers in the event of hydraulic hose

failure

▪ evict persons from the excavation when lifting and placing loads in the excavation

▪ use plant fitted with suitable overhead protection to protect against falling objects

▪ the erect barrier along the edge of the excavation to prevent objects falling into the excavation

▪ use wheel buffers 

Person falling into the excavation

▪ backfill excavation as soon as possible

▪ secure a cover over the excavation

▪ provide safe access to and from the excavation

Person inhaling, or otherwise being exposed to, carbon monoxide or another impurity

of the air in the excavation

▪ as part of the risk assessment process - determine the likelihood of airborne and soil contaminants

being present and the need to undertake formal air monitoring in the excavation

▪ implement control measures necessary for entering and working in a confined space

▪ do not expose persons to a hazardous substance at a level exceeding the international exposure

standard for that substance

▪ monitor the level of any airborne contaminant in the excavation

▪ monitor for explosive gases or vapours

▪ ensure there is adequate ventilation provided to the excavation

▪ use extractor fans to remove airborne contaminants and explosive gases from the

excavation

▪ position vehicles, plant and machinery away from the excavation

▪ provide and use appropriate personal protective equipment, such as respiratory equipment,

protective clothing, safety gloves

▪ remove all sources of ignition if explosive gases are present.

Sheet piling

Sheet piles are commonly used to support excavations in foundation work.

Traditionally, these operations are performed without proper planning especially

during the pre-work stage. Training and information provided to workers also vary in

standards. Sheet piling in the past had a poor record of high accidents, often

resulted in the fatality.

The cause of fatal accidents pertaining to sheet piling was due to one or a

combination of the following failures in ensuring:

▪ adequate depth for interlock of sheet piles or the correct penetration depth.

▪ deviations and leaning (transverse or longitudinal) of sheet piles within

tolerance limit.

It is common in the piling industry to use a cage to lift workers, also called “top man” or

“pile monkey”, onto the top of sheet piles to carry out the aligning or interlocking by

hand. This working process by alternative methods by some contractors can avoid

such hazards.

Depending on the nature of work and site conditions, two alternative methods have

been introduced by using:

▪ threaders and shackle release device

▪ sheet pile trestle

The crane is lifting the sheet pile, interlocking manually in an exposed dangerous position by

the top man.

Workers working at the top of the pile and on the horizontal guide beam

Workers staying on top frame the level can be hit or trapped in between

Threaders and shackle release device:

Proprietary systems used elsewhere have been imported to offer a safer alternative to

this particular process. Some contractors are also beginning to use local-made

models to cut cost. The basic principle of these proprietary systems is to use a

pile-threader and a shackle release device. All the necessary operating procedures

can be done on the ground.

The sheet pile threader is designed for safe and rapid sheet pile interlocking when

sheet piles are being pitched in panels. It replaces the “top man” or “pile monkey” who

normally carries out the interlocking by hand.

The basic method of operation using a universal pile treader is as follows:

The threader is pre-loaded by pulling the pull wires and vice block against spring

pressure and cocking.

The pile to be pitched is lifted until the bottom is at about 1m (3ft) above ground level.

The threader is then clamped onto the pile with the vice. The relative position of the

pile is governed by a stop plate to suit the pile section being used.

With the threader attached, the pile is then lifted by the crane to the end-pile of the

panel.

 By means of the rollers, the lower part of the threader is then clamped to the

last pile in the panel so that the interlocks are adjacent to each other. The clamping

operation is designed to permit free movement of the pile and the threader in a vertical

direction but prevents movement in any other direction. This attachment is normally

done at the top frame level. The cocking device inside the vice slide tubes is then

released.

The crane lifts the pile to be pitched until its bottom edge is above the previous pile in

the panel. The spring pressure on the vice block forces the pile across into the

interlocking position. As the pile is lowered, it interlocks.

 The threader is then unclamped at the top frame level.

Ground release shackle device

The use of these shackles complements the “feet on the ground” approach to piling.

When used in conjunction with the sheet pile threader, there is no need for site operatives

 to go above the safety of top frame level for interlocking sheet piles or releasing the 

lifting shackles

Ratchet release shackles

The ‘shackle release’ is used for lifting steel piles from ground level to some safe vertical

position at any height. It enables these steel elements to be subsequently disconnected safely

and efficiently from a remote location. For pitching steel sheet piles, a sheet pile threader is used

for automatic remote interlocking of adjacent sheets

Another method using a Universal Sheet Pile Threader:

This threader that comes in two pieces can be manhandled and readily operated by

typical site personnel. The unit can be adjusted to suit whatever pile section is being

used on the job site without the need for additional items. The standard threader

requires a different set of guide Rollers for each pile section. When threading single

piles, the threader will readily switch from threading on the left hand to the right hand,

thanks to its unique two-piece design. This means that only one unit is required on the

job site. The threader requires two units for fast threading of single sheet piles – one

set to the left and the other to the right

Universal Sheet Pile Threader

The unit is adjusted to suit the particular pile section being threaded

A different type of threader

Another method using a guide frame fixed with suitable platforms for workers at

intermediate levels

In the past, there had been accidents involving workers falling from the man-cage.

The man-cage had to be lifted up by cranes and attached onto the top of the sheet

piles. When the hooking device of the man-cage failed, the worker fell to the ground

together with the cage. Another case involved a crane. 

When lifting the loaded man-cage, the cage fell during the journey, resulting in the

fatal injury of workers. The safety walkway above provides a safe place of work for workers.

Accidents also occurred in the past when sheet piles are being extracted, which is

rather common locally, after the excavation work is over. Common errors are: buckling

of the jib of the crane or/and overturning of the crane. In fact, tipping of the crane is also a very common scene. This situation happens from time to time, causing repeated overloading of the crane and increasing the chance of overturning.

Advantages of employing a threader:

▪ The sheet pile threader replaces the dangerous, manual operation performed

by a top man climbing or being hoisted up to the top of the piles and

interlocking the piles.

▪ Interlocking piles with the pile threader is faster than any other safe method of

working.

▪ The sheet pile threader makes it possible for piling work to be done under

more severe weather conditions as interlocking can take place even under

high winds.

Safe sheet piling operation depends on good working conditions. The health and

safety arrangements should be periodically inspected and maintained:

Safe storage and handling of sheet piles, struts, king piles, bracing beams and walers.

▪ Proper handling and maintenance of piling hammer/extractor.

▪ Boring machines are in working condition if pre-boring is required.

▪ Lifting cranes are of sufficient capacity, and boom length and bearing capacity

check to ensure safety.

▪ Proper means of transport of excavated materials (No excavated materials

are to be placed near to the pit), as this will affect the well-planned sheet pile

wall operation.

▪ Pumps are in good working condition.

▪ All welding and cutting equipment are in good working order, with proper PPE

in use and the workers involved suitably trained.