The Short Haul Road Nobody Wants to Argue About
You are operating a 9-tonne forward-tipping dumper on a road construction site. An excavator has loaded wet clay and you must move it 150 m to a fill area. The shortest route is a haul road falling about 1 in 8, with a noticeable crossfall towards a soft, rain-softened verge. The surface is rutted and greasy. The alternative is 400 m along a flat, firm haul road, adding roughly four minutes per trip. Your supervisor says "everyone uses the short road". Your skip is loaded to the rated 9 tonnes, and you have it raised a little to clear a ridge across the exit of the loading area. Two other machines are working on the slope section. The handbook in the cab gives a maximum gradient of 20% for travel in line with the slope on firm ground.
1. Which route do you take, and how would you justify it to your supervisor?
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Take the longer, flat haul road unless a competent person has assessed the slope route and put controls in place. The handbook figure does not authorise this descent.
Reasoning you can give your supervisor:
- The 1 in 8 fall is about 12.5% - inside the 20% limit, but that limit assumes a firm, even surface travelled in line with the slope. It says nothing about a crossfall onto a soft verge, ruts and grease.
- A loaded 9-tonne dumper carries its centre of gravity high. A crossfall plus soft ground under one set of wheels is a classic roll-over combination: the low side sinks, the machine leans further, and the load shifts.
- Two other machines on the section means stopping, passing and possibly steering across the slope - all things you should not do on a gradient.
- Four minutes extra per trip is trivial next to a roll-over, an injury and an investigation.
- If the slope route is to be used, it needs: crossfall removed or compensated, the soft verge edged or protected, one-way traffic control, no other plant on the section, and a reduced speed limit. Until then the risk is not controlled.
2. Suppose the slope route is later authorised. Describe how you would travel it, loaded and empty.
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In line with the fall line, straight up and straight down - never across the face of the slope.
Loaded, descending:
- Select low gear before you start the descent; do not change gear part-way down.
- Skip fully lowered and retained - not raised to clear ruts, not raised "just a bit".
- Let the machine crawl, using the brakes lightly and progressively. Avoid harsh braking, which can lock a wheel, induce a slide or pitch the load forward.
- Keep well clear of the soft verge; give yourself margin on the firm side.
- No sharp steering. Steering across a slope shifts weight sideways and is how machines go over.
Empty, climbing back up:
- Same discipline in reverse: in line with the slope, low gear, steady speed, skip down.
- Keep to the agreed one-way control so you are not meeting another machine on the gradient.
If you feel the machine begin to slide, do not fight it with hard steering or stamping on the brakes. Ease off, keep the machine straight and let it settle, then stop and report the condition of the road.
3. Why does it matter that you have the skip raised to clear the ridge, and what do you do about it?
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A raised skip is a stability problem in its own right, before any slope enters the picture.
- Raising the skip lifts the centre of gravity and, when loaded, moves it rearward over the rear axle.
- That increases load on the rear tyres and the ground beneath them - on soft or rutted ground the surface can give way.
- The raised skip acts like a sail in wind and swings the load about as the machine pitches over ruts.
- If a tipping ram or hose fails while raised, the skip drops.
What to do: lower the skip fully before moving off. If the ridge physically prevents it, the ridge is the problem - ask for it to be graded out, or use the flat route, or get the machine repositioned so it can leave with the skip down. Travelling with the skip raised to save time is exactly the sort of shortcut that ends in an overturn.