Ground Bearing Pressure and Outrigger Setup Flashcards

A crane operator is setting up near an excavation. What is the primary concern related to ground bearing pressure in this situation?

Answer: The excavation wall may collapse due to outrigger loads, or the outrigger may break through the edge of the excavation

Outrigger loads near an excavation can cause the excavation wall to collapse or the outrigger to break through the edge of the cut, leading to catastrophic crane overturn. Safe standoff distances from excavations are critical.

When using timber cribbing under crane outrigger pads, how should the cribbing layers be arranged?

Answer: In alternating perpendicular layers (log-cabin style) to maximize stability and load distribution

Timber cribbing should be arranged in alternating perpendicular layers (log-cabin or cross-hatch pattern) to create a stable, interlocked stack that distributes load evenly and resists horizontal shifting.

What is the consequence of operating a crane with only three outriggers fully deployed while one is retracted due to an obstacle?

Answer: The crane's rated capacity must be reduced and only the manufacturer's load chart for that specific configuration may be used

Using fewer outriggers or non-standard outrigger configurations requires the operator to use the manufacturer's load chart specifically for that configuration, which will show significantly reduced rated capacities.

How does a soil's allowable bearing capacity change when the soil becomes saturated with water?

Answer: Allowable bearing capacity generally decreases because water reduces the soil's shear strength

Saturation reduces soil bearing capacity because water reduces internal friction and cohesion in the soil, lowering its shear strength. Wet soils, especially fine-grained soils like silts and clays, can fail at much lower pressures than dry soil.

What is the function of outrigger float pads placed under crane outrigger floats?

Answer: They are placed directly under the outrigger float to create a stable bearing interface between the metal float and the cribbing or ground surface

Outrigger float pads are placed between the metal outrigger float and the cribbing or pad below to create a stable, non-slip bearing interface and prevent the float from sliding on hard surfaces.

Before setting up a crane over an underground utility or vault, what step is most critical to protecting workers and preventing crane damage?

Answer: Contact the utility owner and obtain engineering data on the utility's depth, capacity, and the required standoff or spanning solution before setup

The critical step is contacting the utility owner and obtaining engineering information about underground infrastructure capacity before setting up any crane overhead. Outrigger loads can collapse utility lines, vaults, or conduits, causing crane overturn and utility damage.