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Health, Safety & Environmental Bulletin No 004

25 May 2005 – R Brown

Hiab / Crane Lorry Ground Bearing Requirements

It has been brought to our attention by one of our clients that mobile cranes fitted with outrigger /
stabilizers have had the stabilizer bearing plates sink into the ground when lifting loads, dependent on
rate of settlement may result in a dangerous occurrence, therefore our client has asked contractors to
consider the potential bearing capacity problems with the Hiab crane lorry unit.
Xmo Strata MID validation surveyors already assess the position and general condition of the area in
regard to the hiab unit position, however it is always best practice for the on site team to inspect the
location themselves when the hiab unit is in place, as there may be something that has been overlooked
• Many small lifts of a few hundred kilograms are undertaken on sites using the hiab crane lorry,
these lifts normally rely on the judgment of the operator of the site ground conditions and bearing
spread. The following describes some of the aspects which should be addressed on site if
assessing the lift safety:
Ground Conditions Review The variability of the soil supporting the outrigger spread must be
considered, e.g.:
• Disturbed ground (excavated and backfilled) occurs commonly in site construction, and a degree
of under compaction often results. Often localised voids can be present. Firm crusts of relatively
thin aggregate are often used to form plant platforms on relatively weak and / or waterlogged
geological strata. In such cases although the ground may be adequate for normal construction
traffic, it needs to be regarded with concern when placing outrigger loads
• Care must be taken when positioning the outrigger onto non carriageway class construction
tarmac, as the stabilisers could settle down, into the potentially thin layer
• Other areas of concern the hiab driver or personnel on site must be aware of are as follows; soft
verges, landscaped area, over or adjacent to manhole/access lids, footpaths, over known/suspected
electrical cable or water main service lines, adjacent embankments, basements, pavement stone
etc

• If in doubt follow the advice in CIRIA publication (for cranes) which states that 4 number
200x125x1500long sleepers to be used to increase the bearing area capacity of the stabiliser

“let’s make sure that we continue to make our sites THE SAFEST by helping ourselves, our colleagues,
our customers and even our competitors by improving training, helping where necessary and addressing
any issues of concern there and then”

If you have any quires regarding the Safety Bulletin content or require further information please contact
any staff member of Xmo Strata Ltd.

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