The subbase is the layer of aggregate material that lies immediately below the pavement and usually consists of crushed aggregate or gravel or recycled materials (see Section 6C-1 - Pavement Systems for more information).

What is Sub Base in construction?

The sub-base layer is often the main load-bearing layer of a pavement. It is designed to evenly spread the load of the paving, and any traffic thereon, to the sub-grade below.

What is the purpose of a subbase?

The function of a subbase is to help prevent pumping of fine-grained, subgrade soils. Pumping, which leads to the loss of soil material beneath slab edges and joints, occurs when three factors exist in combination: pumpable soils, excess water under the pavement, and frequent heavy truck loads.