There is no doubt that crane operators work in a high-risk environment, with safety always being the number one priority.
In recent weeks, CICA liaison officer VIC/TAS branch, John Humphries has issued two safety bulletins discussing the importance of ground bearing pressure.
In an exclusive interview with Inside Construction, John discusses the importance of determining ground bearing pressure and why it can mean the difference between a safe lift and a potential disaster.
How important is it knowing the ground pressure prior to a lift and how long is the process to work that detail out?
Ground Bearing Pressure is extremely important as it determines whether a crane and its load will be supported securely before, during and after the lifting work is completed. When ground bearing pressure is underestimated, and is less that the pressure exerted by the crane (via it’s outriggers, tyres or crawler tracks), the entire crane along with its load will begin sink into the ground, become unstable and potentially fall over.
How quick you accesses the ground bearing pressure relies on how much of the following info you possess:
- The type of substrates beneath (there can be many layers of varying thickness)
- The moisture content (Did it rain the night before? Could there be leaking pipes underneath? etc.)
- The amount of compaction or the amount of disturbed substrate. (Has the area been dug up and loosely filled recently?)
If you are not confident in the above, a Geotechnical Engineer specialising in this field to conduct a study can assist.
Are these mandatory assessments for crane operators?
No, but we recommend it when in doubt.
Are these done for every lift, every day in Australia?
No, many lifts are on very hard and very predictable surfaces, so they are not always necessary.
How do you assess ground pressure compositions like rock, soil, mud etc?
See table A as a guide, taken from the QLD Mobile Crane code of Practice.
Or a Geotechnical Engineer would use a Dynamic Cone Penetrometer.
What is it so important to calculate load?
You must always have a greater ground bearing pressure in the substrate beneath the crane, than the pressure that the weight of the crane and it’s load will exert on that ground via it’s supports (tyres outriggers or crawler tracks).
If you underestimate the weight of load, you run the risk of exceeding the maximum capable ground bearing pressure, which means the crane will sink into the ground and become unstable and potentially fall over.