What determines the size of the blocking when blocking under the rigging pads are required?

• A. The height of the load
• B. Ground bearing capacity and ground bearing pressure generated by the crane
• C. The color of the crane
• D. Wind speed

Answer: (B)

Blocking size is determined by how much pressure the ground can safely bear and the load transmitted by the crane through the pads. The goal is to keep the bearing pressure under the soil’s allowable limit, so the ground doesn’t fail or settle excessively. So you size the blocking by dividing the total vertical load on the pads by the ground’s allowable bearing pressure (including safety factors), which tells you the minimum contact area needed. The higher the soil bearing capacity, or the larger the area you provide, the smaller the required blocking. If soil capacity is low, you need larger blocking to spread the load.

Other factors like the height of the load or the crane’s color don’t determine the blocking size. Wind can affect overall stability, but the basic blocking size comes from the load on the pads and the ground’s bearing capacity. For example, a total through-pad load of 400 kN with soil that can safely bear 200 kPa requires at least 2 m² of blocking area (before applying safety factors). In practice you’d pick blocking that provides that footprint with a suitable safety margin.