The lorry crane is parked, the load is slung, and the operator is two levers away from lifting. The one thing nobody has looked at closely is the square metre of ground under each outrigger foot, which is the only thing holding the whole operation up.

Lorry cranes overturn far more often through a setup fault than through a mechanical failure. The machine usually does exactly what it was asked to do. The ground is what changes.

Why the ground decides the lift

A lorry crane on outriggers is a lever. Every kilogram on the hook, every metre of boom radius, and the weight of the machine itself resolve into vertical loads concentrated on four small feet. A modest lift can put several tonnes through a pad no bigger than a dinner plate, and the loading shifts as the boom swings, so the foot carrying the least at the start may be carrying the most halfway round.

Ground that looks solid frequently is not. Backfilled trenches, recently laid turf, and surfaces above buried services can carry a person and a wheelbarrow without any sign of trouble and still fail under a point load. Nothing gives warning, and by the time an outrigger starts to sink the load is already in the air.

Outriggers go out fully

The WSH Guidelines on Safe Use of Lorry Cranes, issued by the Workplace Safety and Health (WSH) Council with the Ministry of Manpower (MOM), are clear that where outriggers are required they must be fully extended and properly secured. The exception is a crane fitted with a manufacturer approved system that accounts for reduced stability at partial extension, and that system has to be working and understood, not simply present.

Partial extension is the shortcut of a tight site, and it is the setup fault behind a large share of overturns. A crane on half extended outriggers has a much smaller stability base than the load chart assumes, so the operator is reading a chart that no longer describes the machine underneath them.

This is core ground covered in a lorry crane operator course, where setup is taught as part of the lift instead of as preparation for it. Understanding how radius, extension, and ground bearing interact is what allows an operator to say no to a position that will not work, which is a decision best made before the slings go on.

Ground you cannot trust

The WSH guidelines name the surfaces a competent person should treat as unsuitable until proven otherwise. On a Singapore worksite, most of them appear within a few metres of each other:

• Grass patches and soft or sandy ground
• Manhole covers and drain gratings
• Excavated trenches and any recently backfilled ground
• Cemented footpaths not designed for vehicle loads
• Slopes, kerbs, and any position where the feet would sit at different levels
• Ground above buried services, basements, or covered voids

Spreading the load with pads and mats

Where the ground cannot take the point load, the answer is to spread it. Timber or composite stabiliser pads increase the contact area so that the same force is carried over a much larger footprint, and heavier mats do the same job on genuinely poor ground. The principle is simple enough, though the sizing is not guesswork: how much area a given foot needs depends on the load coming through it and on what the ground beneath can actually bear, which is why the assessment belongs to a competent person rather than to whoever is nearest the pad stack.

Pads only work when they are used properly. The foot should sit centred on the pad and bear fully across it, not on one edge; the pad should be sound and neither split nor waterlogged; and the load spreading arrangement should be recorded and communicated to the lifting team so the next shift does not undo it. Where a competent person has assessed that additional measures are needed, those measures belong in the lifting plan, not in one person’s head.

The checks before the first lift

A short, ordered routine at the setup stage catches nearly everything that needs catching, and it takes only a few minutes once a crew is used to running it in the same sequence every time.

1. Confirm the ground has been assessed by a competent person and that the position matches the lifting plan.

2. Extend and secure every outrigger fully, unless the crane carries an approved system for partial extension.

3. Check each foot is centred and bearing evenly on a sound pad, with the machine level.

4. Walk the swing path and set the exclusion zone before anything moves.

5. Carry out a test lift, raising the load slightly clear of the ground and stopping to watch for any settlement, list, or movement before continuing.

When the weather gets involved

Ground assessed as sound on a dry Tuesday can behave very differently after a night of heavy rain. Water softens fill, washes out fines from under a pad, and turns a firm surface into something that will settle under sustained load without any obvious sign at the surface.

Singapore’s rainfall pattern makes this a routine consideration rather than an occasional one. Knowing how weather conditions affect safe lifting is part of the operator’s judgement, alongside wind on a large surface area load and reduced visibility during a squall.

Reassessing after rain costs a few minutes. A crane that has settled on one side halfway through a lift costs considerably more, and the recovery is far more dangerous than the original job.

Conclusion

Setup is not the boring part before the lift. It is the part that decides whether the lift stays inside the load chart, and it is where an experienced operator spends attention that a rushed one spends elsewhere. The ground under the feet is the one variable the manufacturer could not design for, which leaves it to the crew on the day.

Wong Fong Academy has trained operators, riggers, signalmen, and lifting supervisors in Singapore since 2011, on machines and ground conditions our learners recognise from their own worksites. Enrol with us and give your crew the judgement that keeps a machine where it should be.

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