What is the purpose of cribbing and mats under crane outriggers, and how do you select proper size?

• A. To distribute load over a larger, more stable surface and avoid ground failure; select mats/cribbing based on crane weight, soil bearing, and manufacturer guidelines.
• B. To increase the crane's height.
• C. To decorate the site.
• D. To reduce crane weight.

Answer: (B)

Distributing the load and ensuring a stable footing is the purpose of cribbing and mats under crane outriggers. When outriggers press down, they concentrate weight on small contact points. On soft or uneven ground, that can cause the soil to deform, leading to sinking, shifting, or even tipping. Mats and cribbing spread that load over a larger, flatter surface, bridge gaps, and raise the footing to a level where the crane remains stable.

Choosing the proper size involves considering the crane’s weight, the footprint of each outrigger, and the ground’s bearing capacity, along with the manufacturer’s guidelines. The goal is to provide enough bearing area so the soil isn’t driven to failure and each outrigger sits on a rigid, level base. Use mats thick and wide enough to handle the load without bending or crushing, and stack cribbing in a stable, interlocked arrangement per guidelines. Always match the setup to the ground conditions and crane specifications to maintain safety and stability.