Truck crane beside a trench with unverified fill
A 50 t truck crane is set up on a recently filled pad beside a 2.4 m deep trench to lift a 3.1 t packaged air-handling unit. The lift radius is 16 m, and the load chart for the current boom length and outrigger configuration shows 4.0 t capacity. Rigging weighs 180 kg. The outrigger floats sit on 600 mm square pads; one rear pad is 1.8 m from the trench edge. The fill is described as 'compacted' but no geotechnical assessment or plate load test is available. The supervisor wants the lift finished before the concrete truck arrives in 40 minutes. Wind is 9 m/s gusting 13 m/s, and the unit has a 2.2 m by 1.5 m sail area. The dogger proposes two nylon slings at a 60° included angle and no tag lines because the unit is 'stable'. The crane has a current annual inspection, but the outrigger beam bubble level shows one bubble outside the painted circle.
1. What is your decision on the lift, and what checks or changes must be completed before any load is lifted? Show the load and ground-pressure reasoning.
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My decision is no lift until the setup is corrected and verified. The load check is close but not the main problem: gross load is 3.1 t + 0.18 t = 3.28 t, which is 82% of the 4.0 t chart capacity. That leaves little margin, and I must confirm the chart notes, hook block deduction and whether the capacity is based on the exact outrigger configuration. The slings are also marginal: with a 60° included angle, each leg carries about 1.64 t vertical and 1.89 t tension, so each sling and shackle must have a working load limit above that after allowing for choke or edge derating. Tag lines are required for load control.
The serious issue is the ground. One rear pad is only 1.8 m from a 2.4 m trench, on fill with no geotechnical verification. I would obtain the manufacturer's outrigger reaction for this configuration, have a competent person or engineer assess bearing capacity and trench-edge stability, and use properly sized mats or steel plates. If the assessment cannot be completed, relocate the crane or reduce the radius. The bubble outside the circle means the crane is not level within the manufacturer's tolerance; I would reset and level all outriggers before lifting.
Wind must also be checked: the unit has a 3.3 m² sail area and gusts to 13 m/s, so I would compare this with the crane's wind chart and the load's permitted wind speed. The 40-minute deadline is not a reason to proceed. A current annual inspection certificate does not approve this site setup.
2. The supervisor says the annual inspection certificate is current, so the setup is 'approved'. How do you respond, and what records or handover would you require?
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I would explain that the annual inspection is a periodic condition check of the crane, not an approval of this particular lift. It does not confirm ground bearing beside a trench, outrigger level, radius, rigging, wind or the lift plan. The operator still has stop-work authority and should not rely on a certificate to accept an unverified setup.
Before lifting I would require a site-specific lift plan showing the crane position, outrigger layout, pad sizes, ground assessment, load weight including rigging, radius, chart capacity, wind limit and exclusion zone. I would complete the daily pre-start check and an outrigger setup checklist, record the level check, and hold a toolbox talk with the dogger and supervisor. If an engineer or competent person sets conditions such as mats, minimum trench setback or reduced radius, those conditions should be written down and signed off. I would record the defect or hold point and notify the crane owner or supervisor. If the supervisor pressures me to proceed, I would escalate rather than sign on.