Explain the uses of Residual soils

Residual soils may be underlain by sloping rock which may contain weathered seams. The possibility of foundations sliding on these seams have to be considered. In one instance, an eight-storeyed building was constructed on a sloping site containing a weak seam of loose soil sandwiched between layers of quartzite with firm rock below. Footings were provided on the quartzite. When the first five storeys were completed, the building began to move downhill and cracks occurred. The structure was salvaged by providing anchor bars and grouting the footings to the firm rock below. Residual soils require careful treatment to identify firm rock from weathered material.