Crane Setup, Site Preparation, and Ground Conditions
What this domain tests
This domain tests whether you can position a mobile crane safely, assess ground bearing, deploy outriggers correctly, and recognize site hazards that affect stability. The exam focuses on load distribution, mats and cribbing, level and compaction, buried services, swing clearance, and the difference between on-outrigger and on-tire ratings.
Core rules and concepts
- The load chart is valid only for the configuration shown: outrigger spread, boom length, counterweight, and quadrant. Fully extend and pin outriggers unless the chart explicitly allows otherwise.
- Outrigger loads are not equal. The worst-case reaction can be much higher than one-quarter of total weight; use the manufacturer's reaction data or a conservative distribution.
- Ground bearing pressure = outrigger load ÷ effective pad area. Increase pad area with mats or cribbing when soil capacity is lower.
- Assess soil type, compaction, moisture, slope, previous excavation, and buried utilities. Disturbed fill and trench edges are high-risk.
- Set up level within the manufacturer's tolerance; verify with the crane's level indicator.
- Maintain clearance from power lines, excavations, structures, and traffic. Barricade the swing radius and keep personnel out.
- Wind, boom deflection, and visibility affect setup decisions; check the load chart notes and site conditions.
Worked example
A crane and load total 50,000 kg. The manufacturer's reaction data shows a worst-case outrigger load of 65% of total weight: 32,500 kg. A 1.5 m × 1.5 m pad gives 2.25 m². Ground bearing pressure = 32,500 ÷ 2.25 = 14,444 kg/m², or about 142 kPa. If the geotechnical assessment allows only 100 kPa, the setup is unacceptable without a larger load-spreading mat or a different position.
Traps that cost marks
- Dividing total weight by four and assuming equal outrigger loads.
- Using the crane's on-tire capacity when the chart requires outriggers.
- Ignoring underground utilities, trench edges, or recently backfilled ground.
- Setting up out of level and expecting the load chart to compensate.
- Forgetting to barricade the swing radius and exclusion zone.