Lifting a Manhole Ring with the Bucket Eye
Four 250 kg precast concrete ring sections have to go into a 1.3 m deep manhole. The 1.7 t mini excavator has a lifting eye welded to the bucket and a rated capacity chart in the cab. The radius you would be working at is 2.8 m, and the chart shows 300 kg at that radius. A 1 m two-leg chain sling is on the van; its identification tag is missing and nobody knows its history. One operative is already down the manhole to guide the ring into position, and the client's representative wants the lift done in the next twenty minutes, before the concrete wagon arrives. The ground is level and firm, and the wind is light.
1. Evaluate this lift against the information given and decide whether you proceed as planned.
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You do not proceed as planned. Working through it:
Capacity margin. 250 kg on a 300 kg rating is about 83% of the stated capacity at that radius, before anything else is added. The chart figure is a maximum for a machine in good condition on ideal ground - it is not a target. Add the sling and its fittings, the lifting eye and bucket, and any dynamic effect from starting or stopping the slew, and the margin is gone. A lift at that proportion of capacity leaves nothing for a slight increase in radius as the boom deflects under load.
The radius is not fixed. As the arm takes the weight, the radius grows. The chart is a set of limits falling with radius, so a lift that starts inside the limit can move outside it during the pick.
The sling is unidentifiable. A sling with no tag and no history cannot be shown to be inspected, tested or rated. You cannot verify its safe working load, and it may have been used for dragging or been shock-loaded and rejected.
A person is in the excavation. He is directly under the load path. If the sling fails, the ring lands on him; if the machine tips, he has nowhere to go.
The machine set-up. A 1.7 t machine is small for a 250 kg pick at 2.8 m even on firm level ground; and there is no evidence yet of a lift plan, a competent appointed person, or the machine's lifting thorough examination status.
Any one of these would warrant stopping. Together they make it a clear no.
2. State what would have to be in place before a safe lift could be made, and who is responsible for each element.
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1. A lift plan, prepared by a competent person. It states the load, the radius at pick and at placement, the capacity available, the sling arrangement and angles, the ground conditions, the exclusion zone and the sequence. Responsibility: the appointed person, with the site manager's authorisation.
2. Verified capacity at the actual working radius. Use the manufacturer's chart for this machine with the correct counterweight and bucket configuration, and keep the working load well inside it, not at 83% of it. If the pick cannot be made inside a comfortable margin, the answer is a larger machine or a different method. Responsibility: the appointed person and the operator together - the operator is the last check.
3. Certified lifting accessories. The sling must be identifiable, marked with its safe working load, and have a current thorough examination (accessories at least every six months). An untagged sling is scrapped, not used. Responsibility: the person supplying and inspecting the equipment.
4. Lifting equipment status for the machine. An excavator used for lifting is lifting equipment: it needs a thorough examination at the required interval, and the lifting eye and its mounting must be in good condition and inspected. Responsibility: the machine owner or hirer, with records available on site.
5. No person in the excavation while the load is over it. The operative guides the ring from outside the exclusion zone with a tag line, and enters only after the ring is landed and released. Responsibility: the appointed person and the banksman.
6. Ground and position checks. Firm level ground, outriggers or blade down if the machine has one, no excavation edge under a track, and a clearly marked exclusion zone under and around the load path. Responsibility: the operator.
7. A briefed team. Everyone knows the signals, the sequence and the stop signal. Responsibility: the appointed person.
3. The client's representative says the concrete wagon is coming and to 'just do it carefully, it has been done this way for years'. How do you handle this, and what alternatives do you offer?
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Handle it as a stop, not a debate. 'Carefully' is not a control - the hazards here are capacity margin, an unidentifiable sling and a person under the load. Say clearly that the lift is not going ahead as set up, and give the reason in one sentence each, because a short factual refusal is harder to argue with than a lecture.
Then move straight to alternatives, so the conversation is about how to get the job done rather than whether to take the risk:
- Change the method: lower the rings with a certified gantry or a telehandler with the right capacity and a proper lift plan.
- Change the machine: bring in a larger excavator with a verified lift plan and chart margin, if one is available today.
- Change the timing: hold the wagon, or have it wait while a certified sling and the machine's lifting examination documentation are produced.
- Change the sequence: land the rings beside the manhole and lower them with the correct equipment when it is on site; the manhole does not have to be built in the next twenty minutes.
On 'it has been done this way for years': that is the same argument as the tape on the hose - experience of the times it worked says nothing about the physics of the time it does not. Note that the practice described is not a method; it is an absence of one.
Record it. Note the instruction, the refusal, the reasons given and the alternative offered, and tell the site manager. If a load is dropped or a person is crushed, the question will be who authorised the lift, and the answer needs to be on paper.