Construction materials can be adversely effected if soils are allowed to intermix because there is no effective separation medium. For example: the load-bearing capacity of a road will be greatly reduced if fine-grained subgrade soil particles intermingle with the road’s granular sub-base.

In these circumstances, two answers that may have been considered in the past are
i) excavating the subgrade to increase the depth of sub-base material, or
ii) using punching-in rock. Both options are timeconsuming and represent a waste of     costly materials.