Concrete Pump Outrigger Pads: Getting the Ground Right Before the Boom Goes Up

Strip the badge off the side of the vehicle and a boom pump's outrigger arrangement is doing the same job as a mobile crane's — four legs spread out from a chassis, holding up a long arm that's been extended and slewed away from the centre of the machine. Push that boom out and round to one side and the stabiliser nearest the load takes a disproportionate share of the reaction. It's the same leverage that makes crane outrigger loading uneven, and we see it catch people out for the same reason: the plate on the side of the machine gives a static weight, not the loading at full reach.

What a pump adds on top is something a crane never has to deal with — concrete actually moving through the boom under pressure. Pumping isn't a steady, gentle load. It pulses as the piston strokes, and that pulsing runs straight down the boom and into the outriggers as vibration and cyclic loading, on top of the static reach load already sitting there. We've watched ground that would just about cope with a dead weight behave very differently once it's being worked by a machine that shudders slightly every few seconds for the length of a pour.

There's a structural reason concrete pump stabilisers so often sit on unreliable ground, and it isn't bad luck. A pump is set up close to whatever it's feeding — and what it's feeding is very often a foundation, a basement, a retaining wall, or a slab right next to a trench. That means the stabiliser footprint regularly lands on an excavation edge, a kerb line, made-up ground, or backfill that was compacted last week and hasn't had time to settle.

Compare that with a crane pick, which can often be positioned wherever the ground is best across a wider site. A pump has far less choice. It goes where the pour is, and the pour is usually right next to the one bit of ground on the whole plot least able to take a concentrated load — recently disturbed, poorly compacted, or simply too close to an edge for comfort. In our experience, treating that ground as equivalent to the compacted hardstanding twenty metres away is where overturns start. Ground support failure under plant stabilisers is a well-recognised hazard category in UK construction, and boom pumps sit squarely inside it.

Pump jobs tend to be short. A pour might need the machine on site for an hour or two, then it's gone. That short duration creates a particular temptation we see on site again and again — skip the proper ground check because it's not worth the fuss for such a brief job, and just get the legs down and the boom up so the wagon can start feeding.

The load doesn't know how long it's going to be there. A stabiliser leg pressing into weak ground for ninety minutes of active pumping is under exactly the same pressure as one left there for a week — arguably more, given the vibration coming off the pour itself. In our view, short duration is a scheduling fact, not a structural one, and it shouldn't be allowed anywhere near the decision about whether the ground gets assessed and packed out properly.

This is the same problem we solve for crane teams every day, and the same fix applies: spread the point load from each stabiliser foot across enough ground that the bearing pressure drops to something the surface can actually take, rather than concentrating it under a single steel pad. Load spread is the whole game here.

We build ALIMATS® as a patented, modular aluminium mat system in 6005A alloy, designed to sit under exactly this kind of concentrated leg load. Modules run from the Mini panel at 0.58 x 0.58m and just 13kg, through Short, Standard and Long formats, up to the Extra Long 3480 x 290mm module at 48kg — giving configurations from 1.34m2 to 8.07m2 depending on what a particular stabiliser foot needs. Every configuration carries a safe working load rating we've had verified independently by a Fellow of the Institution of Structural Engineers, and SWL across the range runs up to 80 tonnes — comfortably beyond anything a boom pump leg is going to put through it.

The bending-test figures are the part that matters most under a stabiliser specifically, because a stabiliser foot is a concentrated point load, not a spread one. ALIMATS deflected in single millimetres across the same test loads where a competing UHMWPE plastic mat deflected in tens of centimetres — the full rig and figures are in our aluminium vs plastic bending test. That gap is the whole argument for aluminium over plastic under a pump leg: a mat that flexes tens of centimetres under a point load isn't spreading that load evenly into the ground beneath it — it's funnelling it straight back down through whatever part of the mat happens to be under the foot.

Pump hire is charged by time, and a pump standing idle while someone hunts for boards to shove under the legs is a pump costing money and holding up a concrete delivery that's already on the road. That commercial pressure pushes hard against anything that needs a forklift, a telehandler, or a delay to fetch extra plant just to get matting in place.

ALIMATS modules are handleable by two people with no heavy plant needed, which is precisely what a pump crew setting up in a tight window wants. Panels go down, the legs come out onto them, the boom goes up, and nothing else has to arrive first. We inspect, clean and check every mat before it goes back out, and we run the range on day, week or long-term hire as well as outright purchase — delivered 24/7 across the UK on our own FORS Bronze-accredited fleet, which earns its keep every time a pour gets pulled forward or pushed back at short notice.

How much mat you need under a given stabiliser foot comes down to the leg load, the ground's bearing capacity, and how much margin you want against the vibration a working pump adds on top of its static weight. The sizing calculator below runs through those figures and suggests an ALIMATS configuration for your setup — worth a couple of minutes before the pump arrives, not after it's already sinking.