Wheel Loader Stockpiling Near a Six-Metre Platform Edge After Rain
A 3 m³ wheel loader is building a spoil stockpile on a raised platform that will later carry a piling rig. The platform edge drops about 6 m to a live haul road. The concrete-block edge protection was removed last week so a delivery lorry could turn, and has not been replaced. Overnight rain has softened the fill and the loader's tyres are cutting ruts around 200 mm deep. The current stockpile toe is 2.5 m back from the edge. The banksman has been told to stand "behind the loader so I can see him in the mirror". A tipper has arrived and is reversing towards the stockpile without a banksman. The loader is pushing material towards the edge with the bucket raised. A crack has appeared in the platform surface roughly 4 m back from the edge.
1. Assess the 2.5 m set-back and the crack. What do they tell you, and what should happen immediately?
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The crack is the decisive observation, not the 2.5 m.
Two metres of set-back is a common rule of thumb for a stockpile toe on firm ground, so 2.5 m might look acceptable on paper. But the set-back figure only has meaning when the ground behind the edge is intact. A tension crack running parallel to the edge, 4 m back, is the surface expression of a failure surface developing inside the platform - the soil mass between the crack and the edge is already separating. The stockpile toe is inside that mass.
Contributing factors, all pointing the same way:
- Rain-soaked fill and 200 mm ruts mean the surface layer has lost shear strength and the machine is loading it dynamically.
- The spoil surcharge is applying a horizontal push directly towards the edge.
- The edge protection was removed, so there is no physical barrier and no warning to any driver.
- Pushing with the bucket raised puts the heaviest part of the machine and its load forward, close to the edge.
Immediately: stop the loader, bucket grounded, engine off. Stop and hold the reversing tipper. Clear all personnel and plant from the area between the crack and the edge and from the haul road beneath. Barricade the zone at the crack line - not at the edge. Then have a competent person, and geotechnical advice if the platform is engineered fill, assess the platform before anything returns to it. Nobody drives on a tension crack to "test" it.
2. Once the platform is declared fit to work, describe how the loader should place material without approaching the edge.
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The principle is that the machine never travels to the edge with a load, and the material is placed by a method that builds its own barrier.
- Reinstate edge protection first - a properly anchored barrier or a designed berm, set back from the edge by the distance the competent person specifies, not a token line of blocks.
- Dump short, push out. Tip the bucket on firm ground well back from the edge and push the material forward in a controlled windrow, rather than carrying a full bucket to the lip. The loader's centre of gravity stays behind the set-back line throughout.
- Build a berm as you go. Deliberately leave a ridge of material at the set-back line, at least a bucket height and wider than a wheel, so that every later push is against the berm rather than into free air. The berm is the working edge until final trimming.
- Keep the bucket low when pushing. Raised bucket plus forward travel on soft fill is the classic over-the-edge configuration.
- Work parallel, not nose-in. Approach the stockpile at an angle and turn away, so the machine's path never points at the drop.
- Control the tipping operation separately: the tipper reverses only with its own banksman, on a marked line, and stops short of the stockpile so the loader does the pushing.
- Inspect the surface for fresh cracking before each shift, and after rain.
3. The banksman's position and the unsupervised tipper are both communication failures. Explain why, and set out a control that actually works.
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Why both fail:
- "Behind the loader so I can see him in the mirror" inverts the purpose of a banksman. He is there so the operator can see what the operator cannot - the edge, the stockpile toe, the ground, people. Standing behind the machine puts him in the operator's mirror but out of the hazard area's sightline, and the mirror view of a person directly behind a 3 m³ loader is poor at the best of times. If the operator has to reverse, the banksman is now in the path.
- An unsupervised tipper is a second machine, with its own blind spots, arriving in a shared area with no agreed stopping point, no signal protocol and no one empowered to stop it. The loader operator cannot control a reversing lorry and his own bucket at the same time.
A control that works:
- One banksman, dedicated to the tipping area, positioned where he can see the edge, the stockpile and both machines, and where both operators can see him - usually to the side, outside the reversing path, never behind.
- A marked stop line for tippers, agreed signals briefed to both drivers, and radio or hand signal contact maintained into the loader cab.
- A single controller for the area: one person decides who moves and when. Two machines moving at once in a soft-edged area is the condition to eliminate.
- Authority to stop. The banksman must be able to halt the tipper and the loader without needing permission - and that must be stated out loud at the briefing, not assumed.