Tipping accidents with concrete boom pumps have occurred as a result of:
- Inadequate cribbing
- Misjudging the soil
- Poorly compacted soil
- Setting up too close to excavations or backfilled areas
- Hidden voids
- Natural or man-made voids
Setting the outriggers of a concrete pump with a placing boom is one of the most critical jobs of the concrete pump operator and should always be done in accordance with the manufacturer's recommended procedure. If not done properly, it can lead to a serious accident. Tip-over accidents can be avoided if people take precautions when the unit is set up. Both operators and contractors must be aware of the potential danger that exists when a large boom is unfolded and extended over outriggers. If the contractor remembers to offer additional cribbing and if the operator remembers to ask for it when it isn't offered, the problem can be minimized even before the boom is extended.
Here are some rules to follow when setting outriggers:
- Do not set the outrigger on uneven soil. If necessary, reposition the unit or level the soil.
- Do not set the outrigger on a hill. The force of the machine weight must be transmitted straight down, otherwise the outrigger load would be partially down and partially sideways, putting undue strain on the outrigger leg.
- Do not bridge a hole with outrigger cribbing. If there is no soil contact over the hole, the pressure on the ends of the pad is much greater. The soil could give way or the cribbing could break.
- If you determine that you need five pieces of cribbing to support the load but the foot only touches three of them, the outrigger will sink into the soil. To avoid this problem, lay dunnage the opposite direction on top of the first layer. The top layer of dunnage must contact all pieces that are supporting it.
- When jacking, put the full weight of the truck on each outrigger, one at a time, and if the pad starts to sink, retract the foot and supply more cribbing. Continue this process until the outrigger appears stable and the pad shows no sign of sinking. Only then are you ready to unfold the boom.
- If you are unable to get the outriggers to stabilize, do not unfold the boom. Relocate the pump to a location that will support the weight of the outriggers.
Cribbing: more or less?
- More is better
- The stronger the material, the better
- Pay close attention to the type of soil where you're setting up the unit.
Every person in the chain of a pumping job has a responsibility to help protect the hose person and other nearby personnel. Education is the key, followed closely by diligent watchfulness and personal protective equipment. Educational materials are available from the American Concrete Pumping Association, and everyone involved in the concrete pumping process should be trained, including:
- Job superintendents
- Labor foremen
- Pump operators
- One of the things a contractor can do to help is to order the right size boom. If the boom is too small, the operator may have to set up too close to an excavation to reach the pour; if the boom is too large, it will require much more cribbing than a smaller unit.
- Have a place prepared for the pump before it arrives on the job.
- Inform the pump operator of backfilled areas, soft or muddy areas, or underground obstructions.
- Have cribbing near the setup area prior to the pump's arrival (including steel sheets if the soil is known to be bad).
- Monitor the setup. Don't let the operator cut corners or take chances.
When the contractor calls to order the pump the dispatcher should:
- Learn the size of pump that is needed and send that size if possible.
- If availability means that a unit that is larger or smaller than necessary will be sent, warn of possible complications.
- Ask about soil conditions or underground obstructions.
The operator is ultimately in charge and must make good decisions regarding setup, including:
- Use as much cribbing as practical; too much is better than too little.
- Watch for all warning signs prior to setup.
- Watch for sinking outriggers while unfolding the boom, and continue to recheck them throughout the day.
- Keep people out from under the boom whenever practical.