Modeling and Prediction of the Effects of Moisture on the Unconfined Compressive and Tensile Strength of Soils

Unconfined compressive strength (UCS) and tensile strength are important geomaterial parameters that are used for performance prediction and mix design. Both UCS and tensile strength are affected by gravimetric water content and thus the characterization of their relationship with gravimetric water content is of paramount importance. The unified effective stress theory based on the suction stress enables the characterization of soils under both saturated and unsaturated conditions with one closed-form relationship. Using two types of soils, this paper provides experimental verification of this effective stress theory through indirect tensile (IDT) and UCS tests. The verification is extended to low gravimetric water contents and high matric suction levels. A new method is proposed to predict a soil's UCS and tensile strength at specified gravimetric water contents by characterizing the soil water characteristic curve (SWCC) and conducting UCS and IDT tests at different unsaturated gravimetric water content levels, which is verified experimentally in this paper. The mechanical properties of soils are related to the material parameters a (inverse of the air entry pressure for water-saturated soil) and n (pore size distribution) of the SWCC. (C) 2015 American Society of Civil Engineers.