All MEWPs rely on the condition of the ground on which they stand for their stability. This applies equally to those which require the use of jacks or outriggers and those which operate free on wheels.
Poor ground may well settle when subjected to the loads of MEWP wheels or outriggers and this in turn will result in the machine being out of level and becoming unstable.
Consequently it is essential that an assessment of ground conditions is made before travelling, using or setting up a MEWP on any surface.
Ground Assessment
The assessment of ground strength can vary from a visual inspection of the ground surface to a full geotechnical survey. In the case of MEWPs a visual inspection is often adequate, as outrigger loads are relatively low compared with machines such as mobile cranes. However, it is essential that the assessment is made by persons with adequate knowledge and experience to know when further expert advice and assessment is required.
Ground Condition Hazards
Some typical ground condition hazards that may be encountered are:-
Uncompacted Fill
Soil or other fill material might be piled along the line of a backfilled trench without being compacted. Cracking of the ground along the line of the trench is an indication of uncompacted fill.
Proximity to Excavations
MEWPs should not be positioned near to the edge of trenches and other excavations as these are likely to collapse without warning. If the machine needs to be used close to the edge of a slope or excavation, with the outriggers or wheels in the “danger area”, an engineering assessment must be by a competent geotechnical engineer before the MEWP is set up and operated.
Floors Cellars and Basements
Many floors, cellars and basements are incapable of bearing the weight of a MEWP and could collapse without warning. The strength of floors and location of cellars and basements must be taken into account when siting MEWPs.
Paved Areas
Paved areas can look deceptively strong but might have been laid on weak ground underneath. Footpaths should be considered to be suspect as there could be weaker material or shallow services underneath the surfacing. If a road is used regularly by heavy commercial vehicles and does not show any signs of distress it is of less concern than a lightly trafficked car park or estate road.
Underground Services
Sewers, drains, manholes, gas and water mains, etc. might be damaged by the weight of a MEWP or could even collapse and cause the MEWP to become unstable or overturn.
Weather Conditions
Heavy or prolonged rain can alter ground conditions and cause sinking of outriggers or wheels. If it is suspected that the ground supporting a MEWP is getting softer regular checks should be made on machine level and the appropriate adjustments made to outriggers, packing mats etc. Regular checks should be carried out when frozen ground is thawing out since frozen ground can appear to be much firmer than it actually is.
For further information on this subject, please refer to the following link: http://www.ipaf.org/en/publications/technical-guidance-notes/ or contact Warren Access on 0191 236 7120.
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