ABSTRACT
Civil engineers build on or in the earth’s surface (Ng& Menzies 2007). A large portion of the earth surface is found in semi-arid and arid regions where the groundwater table is deep because the annual evaporation from the ground surface in these regions exceeds the annual amount of precipitation (Fredlund & Rahardjo 1993). The land surface in semi-arid and arid regions may be comprised of notoriously hazardous geomaterials called “unsaturated soils”. These soils are hazard to slopes, earth structures and earth-supported structures because on wetting by rain or other means, they can expand or collapse; on drying by evaporation or other means, they can desiccate and crack with serious consequences for safety and high costs. Among unsaturated soils, some are particularly problematic for engineers, for example, expansive plastic clays commonly found in Colorado and Texas, USA, in Hubei and Shandong, China and in Madrid, Spain (Ng &Menzies 2007); loess soils commonly found in Missouri and Wisconsin, USA, Ningxia and Shanxi, China (Liu 1988) and in Kent, Sussex and Hampshire, United Kingdom (Jefferson et al. 2001); and residual and saprolitic soils located above the ground water table, particularly at many hillsides in Brazil, Portugal and in the Far East such as Hong Kong and Malaysia.
