Site Set-up, Ground Conditions and Outrigger Use
Ground bearing is the foundation of every lift
The crane's capacity assumes a stable support. Ground bearing pressure under an outrigger pad can be several times the load on that outrigger. You must assess the ground: type, compaction, voids, services, slopes and drainage. Soft or filled ground, recently excavated areas, basements and service trenches are red flags. Use spreader mats or crane pads sized to distribute pressure. The trap is assuming mats fix everything; they only help if the ground beneath can carry the distributed load.
Outrigger configuration
Fully extend outriggers unless the chart specifies a reduced spread. Deploy pads on firm, level ground. Keep the crane level within the manufacturer's tolerance; out-of-level cranes induce side loading and reduce capacity. Check clearance from excavations, and remember that outrigger loads can affect buried services and retaining walls. Never pack under a single outrigger with loose material.
Set-up checks
Confirm the slew path is clear, the tail swing is barricaded, the crane is positioned to minimise radius, and the load can be landed without fouling. Verify wind limits for the boom configuration. Establish the exclusion zone and the rigger's position before lifting.
Worked rule of thumb
If an outrigger carries 30 t and the pad is 1 m × 1 m, the pressure is 30 t/m² (about 300 kPa). On soft clay with a bearing capacity of 100 kPa, you need a pad of at least 3 m², or about 1.75 m × 1.75 m, plus a safety margin.