Magic Glasses: Sloping Ground and Outrigger Pads
- Mar 16
- 4 min read
At first glance, a crane on a hill can look fine. The crane is level, the outriggers are down, and the lift looks ready to go. Put the Magic Glasses on, and you notice something else - the setup under the legs may be carrying the load, but that does not mean it can hold its position.
Quick Scene-Setter
A crane is set up on a sloping sealed surface.
One side has been packed up to get the crane level. There is a wedge in the stack. Under the outrigger foot is a synthetic pad sitting on the road.
From a distance, it looks normal.
The crane is level. The pad is in place. The lift looks straightforward.
What Most People See
Most people see a standard setup.
They see:
a level crane
outriggers down
packing under the foot
a pad spreading the load
They assume the issue has been dealt with.
The crane is level, so the setup must be safe.
What the Magic Glasses Show You
This is where experienced people see something different.
On flat ground, the support under the outrigger mostly has one job: to spread the load into the ground.
On a slope, it has another job as well.
It also has to resist movement.
That is the part people miss.
As the crane operates, the load on each outrigger varies. One leg may bear more weight while another bears less. This means the support beneath the foot is not only subjected to a vertical force but can also experience forces that cause the stack to creep or slide. That is why wedges do not automatically resolve the issue.
They may help level the foot.
They do not remove the sliding risk.
This is also why plastic or nylon pads on asphalt can be dangerous. The crane may be level, but if the bottom interface is too slippery, the whole support system can move when the outrigger loads change.
So the real question is not:
“Is it level?”
The real question is:
“What is stopping it from sliding?”
The Controls That Matter
Do not stop at checking level. Check what the bottom pad is sitting on.
Look at the full stack, not just the top:
Foot → pad → packing → wedge → ground surface.
Treat wedges carefully. They may level the setup, but they do not prove it is secure.
Be cautious with plastic or nylon pads on sealed, smooth, or wet surfaces.
Do not assume a bigger pad solves the problem.
Bigger helps spread the load. It does not always improve grip.
Build a support arrangement that is stable and resistant to movement, not just level.
Think about the lowest contact surface. That is often where the real problem is.
Where possible, reduce the slope by cutting the ground or building it up and compacting it, rather than relying on wedges and stacked packing to level the crane.
Also consider how the setup will behave as the crane:
changes radius
slews
redistributes the load between the outriggers
When the setup is outside normal conditions, involve an engineer. A competent engineer may be able to make the arrangement safer by assessing the slope, the likely horizontal forces, the friction at each interface, the pad and packing arrangement, and any extra restraint needed.
Do not rely on guesswork or rules of thumb for sliding resistance. This needs to be assessed for the actual surface, materials, and lift conditions.
If the crane can only be made level by building a support stack that may move, stop and rethink the setup.
Magic Glasses Checklist - Sloping Ground and Outrigger Pads
Ask yourself:
Is the crane level because the ground is right, or because the packing is compensating for a bad surface?
What is the bottom pad sitting on?
Could that surface let the pad slide?
Is there a wedge in the stack?
Is the pad material suitable for the surface under it?
Will the support still hold position when the outrigger loads change?
Have you checked for sliding risk as well as ground pressure?
Does the setup still look right once you think about movement, not just weight?
Is this a standard setup, or does it need engineering input?
A crane on a slope can look safe at first glance. That is why this catches people out. The support under the outrigger is not only there to carry weight. On sloping ground, it also has to stay in place as the load shifts.
That is what trained people learn to see. Next time you look at a crane set up on a hill, do not just ask whether it is level.
Ask:
What is actually holding it in place?
Because a crane can be perfectly level -
right up to the moment the support stack starts to move.
Magic Glasses: The magic glasses come from the reality of - when I look at my books, I don't see a problem. But when my accountant looks at the books, it's a whole different story. He must have a special set of glasses.
As PCBU's, Officers and Workers, we have an obligation to learn what we are up to and the risks. Our actions and the standards we accept also affect those around us. This magic glasses post is made to help others see what we see.
