Beneath the Chassis: Evidencing Ground Conditions for MEWP Set-Up
MEWP stability is usually discussed in terms of levelling, outrigger deployment and operator behaviour. Those matters are important, but they begin with an assumption that the ground can carry the load. When that assumption is untested, a machine can appear level, pass a visual check and still be poorly supported. For facilities managers and contractors, the ground-condition survey should therefore be treated as a formal pre-deployment handover step, with evidence that can be reviewed by others.
Start with the machine's load envelope, not the surface
Ground surveys are only meaningful when they are related to the intended machine and configuration. Before assessing paving, tarmac or landscaping, obtain the manufacturer's load chart and identify the maximum outrigger or wheel load for the specific boom or scissor configuration. The figure should include the effects of full outreach, basket load, wind and any site-specific allowances required by the manufacturer.
For outrigger machines, the load is concentrated at the pad, so a single point can exert considerably more pressure than the machine's gross weight divided by four. The survey should record the load figure used, the pad size and the proposed load-spreading method. Where the manufacturer's data is ambiguous, or the machine will be used near the limit of its chart, the assessment should be escalated rather than resolved by assumption.
Investigate what the surface conceals
Visual inspection is necessary but rarely sufficient. Beneath a neat layer of block paving may be a drainage run, a service duct, a basement roof or a former inspection chamber. In light industrial premises, suspended slabs and basement decks are common, and their capacity may be far below that of ground-bearing concrete. Made ground, old foundations and landscaped areas can also produce local voids or variable support.
The survey should draw on available drawings, service records and previous site knowledge. Where records are missing or inconsistent, a trial pit, survey scan or structural assessment may be required. The person signing off the survey should be competent to interpret those findings; a visual check by the operator alone is not a substitute.
Check slope, edge distance and drainage
Level is not the only geometric issue. Crossfalls, cambers, ramps and kerb transitions can place a machine outside the manufacturer's tolerance before the basket is raised. Measure the slope rather than relying on appearance. Edge distance matters too: excavations, retaining walls, loading bays and made-up ground can reduce support even where the surface looks intact.
Drainage is part of the same picture. Water running across a site may soften the ground beneath an outrigger pad during the shift, particularly after prolonged rain. The survey should identify low points, gullies and areas where water collects, and the handover should set out how those areas will be avoided or monitored.
Account for weather and changing conditions
Ground conditions are not fixed at the start of the day. Rain, frost and thaw can change the bearing capacity of granular surfaces, landscaped areas and temporary haul roads. A survey completed in dry conditions may not remain valid after overnight rainfall. The handover should therefore include re-inspection triggers: heavy rain, freezing conditions, a thaw, changes in drainage, or any movement observed around pads. Where conditions are marginal, the machine should not be deployed until the ground has been rechecked and, if necessary, the load-spreading arrangement revised.
Use load-spreading as an engineered measure, not a habit
Spreader pads and track mats can be effective, but they need to match the load and the ground. Proprietary outrigger pads should be used in accordance with the manufacturer's instructions and the geotechnical assumption behind their selection. Offcuts of timber may be unsuitable if they are not sized, graded or inspected for the load. On soft ground, a larger pad may reduce pressure, but it will not bridge a void or compensate for a buried service.
The survey record should state the type and size of pad, the bearing pressure assumed and who confirmed the arrangement. If the ground is a suspended slab or basement roof, the assessment should involve a structural engineer or temporary works adviser rather than relying on mats alone.
Record the survey and hand it over
A survey that is not recorded is difficult to defend and easy to ignore. A useful record includes the date and time, site location, machine type and configuration, the load figures used, surface type, findings from drawings and inspection, photographs of the proposed positions, slope measurements, pad details and the name of the competent person who signed it off. It should also state the stop criteria and re-inspection triggers.
The record should be attached to the MEWP handover and, where the site operates a permit system, to the relevant permit. The operator should be briefed on the assumptions behind the survey and told to stop if the ground changes or the machine cannot be set up as planned.
Define stop criteria clearly
Clear stop criteria prevent debate at the point of deployment. Examples include an unidentified void, a drain or service under a pad, insufficient load-bearing information, a slope outside the manufacturer's limit, standing water, a basement roof without confirmed capacity, or a conflict between drawings and site conditions. The operator should have authority to stop, and the machine should not be repositioned onto an unassessed area without a revised check. This is not bureaucracy; it is the practical means by which a stable set-up is confirmed rather than assumed.
The basket is where the work happens, but the set-up begins beneath the chassis. By making the ground survey a documented part of the handover, facilities teams and contractors can reduce the risk of a stability incident that no amount of operator skill would have prevented.
