Granular Sub Base (GSB) is natural or crushed material, used for road construction as a sub-base layer . Granular Sub Base (GSB) is a fundamental component used in road construction, serving as a sub-base layer. Whether sourced naturally or created through artificial means, GSB consists of crushed aggregates that are utilized in granular form. Positioned above the subgrade layer and below the base layer, this essential layer is commonly referred to as the granular subbase.