MEASUREMENT AND ESTIMATION OF SOIL WATER CHARACTERISTIC CURVE FOR FOUR UNSATURATED TROPICAL SOILS.

Infrastructures are mostly built on unsaturated soil in the tropical region such as Nigeria, yet soil investigations and designs are based on saturated soil mechanics owing to difficulties associated with soil suction measurements using direct methods such as pressure plate extractor, triaxial testing equipment for testing unsaturated soil, etc. Soil water characteristic curve is an important parameter for estimating unsaturated soil property function. This research considered an indirect method (filter paper) of laboratory soil suction measurement (which is relatively simple, fast and inexpensive) and predictive correlation equations for estimating soil water characteristic curve from index properties of soil for four unsaturated tropical soils of Nigeria, three predictive correlation equations were used in this research namely; Navid et al model (2012), Zapata et al model (2000) and Witczak model (2006), the soil water characteristic curve constant parameters computed from these models were fitted through either Van Genuchten model (1980) or Fredlund & Xing model (1994). Results of air entry values of soils from experimental work and predictive correlation equations were in close range which indicated that in spite of the difficulties experienced in performing laboratory suction test, the predictive correlation equations such as the ones used in this research were found to be proper for estimating soil water characteristic curve. [ABSTRACT FROM AUTHOR]