Foundation, base and base jacks

Look at what the scaffold will stand on: solid paving, compacted gravel, topsoil or freshly cast concrete have very different bearing capacities. Soft, waterlogged or newly backfilled ground can settle under load. If you are in doubt about a heavy scaffold on soft ground, the ground pressure must be assessed geotechnically (Eurocode 7) — the indicative ground pressure values in the calculator do not replace an assessment of the actual ground.

On anything other than hard, level paving, sole boards (base boards/footing blocks) are placed under the base plates. They spread the concentrated standard load over a larger area so that the pressure per m² falls and the spindle does not sink into the ground.

The softer the ground, the larger the base plate — you reduce the pressure by increasing the area.

A plank/board under the jack spreads the load diagonally down into the ground. The scaffold calculator assumes a spread of 2:1 along the grain and 1:1 across it, so the effective bearing area is larger than the base plate itself. It is this effective area that the ground pressure must be distributed over — not just the plate's footprint.

The adjustable base jacks compensate for differences in height in the ground so that the first frame can stand level. The jack may be extended by max. 0.20 m (BFA); if more is needed, the ground is levelled or a special tall base is used. An over-extended jack loses stability and can deform.

The base plate must lie flat against the sole board with full contact. If it rests on a corner or rocks, the entire standard load is concentrated at one point, and both the plate and the ground are overloaded locally. Check each individual base before building up.

A rocking base plate bears on only one corner — correct it before you build further.

With the screw jacks adjusted, the bottom row of bays is set precisely level and plumb and checked diagonally. The base is the reference for the whole structure: an error of a couple of centimetres at the bottom becomes several centimetres of skew at the top.

The permitted ground pressure depends on the soil type and is geotechnics (Eurocode 7 / DS/EN 1997) — not a fixed scaffold figure. The principle is that the pressure under the plate must be less than or equal to what the ground can bear; otherwise the scaffold will settle. For heavy scaffolds or uncertain ground, involve a specialist.

Record the ground assessment and any base plates in the QA log. The foundation is not 'finished' after erection: at inspection, check that the screw jacks have not settled, that the contact surface is still full, and that the 0.20 m limit is still met after e.g. rain.