Pick-and-Carry Down a Site Ramp With a Leaking Tyre
A 50 t rough-terrain crane is to pick up a 6 t generator on a pallet and carry it 80 m along a site haul road. The route includes a 1:10 downhill slope and a 90-degree turn. The manufacturer's pick-and-carry chart gives 6.5 t at 10 m radius on level, firm ground with the boom retracted. The chart also requires reduced capacity on slopes and with the load close to the ground. One rear tyre is at 8 bar but has a slow leak and is visibly softer than the others. The generator has a high centre of gravity. The supervisor wants the load carried about 1.5 m above ground to clear a raised curb on the inside of the turn, and no taglines are planned. The operator has carried similar loads on level ground before.
1. Should the operator carry the generator as proposed? Justify your decision with the numbers and conditions.
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No. The proposed carry already uses 6/6.5 = 92% of the level-ground pick-and-carry capacity, before any allowance for the 1:10 slope, the turn or the soft tyre. The manufacturer's chart is for level, firm ground with the boom retracted; a 10% slope reduces capacity and changes braking and steering. The 90-degree turn introduces side loads that a pick-and-carry chart may not cover. The soft tyre is critical: tyre capacity and crane stability depend on correct inflation, and a leaking tyre can fail under a 6 t load. Carrying the high-centre-of-gravity generator 1.5 m above ground raises the load's centre of gravity and increases swing, especially without taglines. The operator's previous experience on level ground does not justify this route. The carry should not proceed until the tyre is repaired, the route is assessed and the chart conditions are met.
2. What conditions would make a pick-and-carry acceptable, or what alternative should be used?
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The tyre should be repaired or replaced and all tyre pressures set to the manufacturer's values. The route should be surveyed for slope, bearing capacity, overhead obstructions and the turn radius. The manufacturer's pick-and-carry chart must be checked for the actual slope and configuration, with the boom retracted and the load reduced if required. The load should be carried as close to the ground as the chart allows, typically a short distance above ground, not 1.5 m. The curb should be removed, ramped or avoided rather than raising the load. Taglines should be used, the area should be barricaded, and a banksman should escort the crane at walking pace. If these conditions cannot be met, the generator should be moved on a flatbed or the crane repositioned and the lift made with outriggers. The lift plan should be amended and approved by the lifting supervisor.