Most road pavement failures are propagated through the physical infiltration of water into expansive subgrade soils (moisture increase and suction decrease). In road design and construction, the normal and conventional practice in providing counter-measures to the inferior properties of problematic soils in Africa is to replace them altogether with a capping layer consisting of superior materials meeting the required specifications.

However, most specifications on such material often require replacement depths of d≥1m without scientifically determining the appropriate and/or optimum depth of replacement required in relation to characteristics of the subgrade soils as well as the capping superior material. This usually leads to unnecessarily high costs of earth works. On the other hand, in cases where there are no particular specifications, the replacement depth is determined arbitrarily leading to premature failure of the pavement structures in most cases.

The Replacement and Capping (ReCap) Technique, developed on scientific and mathematical basis, introduced in this Study, provides a more precise approach to determining the layer thickness (quantity) of subgrade inferior material that is to be replaced and capped, modeled as a function of the physical, chemical and engineering properties of both the superior and problematic geo-materials. The method also specifies the criteria to be applied when the material properties lie on the Boundary Limit (BL) in relation to the intrinsic characteristics of the particular material such as clay and colloidal activity, Atterberg Limits, swell and other physio-chemical properties.