Study on the relationship between matric suction, unconfined compressive strength, and uniaxial tensile strength for compacted expansive soils

The uniaxial tensile strength (UTS) of soils is conventionally considered as a fraction of suction stress and suction stress is believed to be the product of matric suction and the kth power of effective saturation. The effective saturation is hard to be accurately determined while k, a parameter used to balance the surging matric suction as the soil dries, is rather ambiguous in its physical meaning. This study aims to develop an equation for describing the relationship among matric suction, unconfined compressive strength (UCS), and UTS. To this end, two stages of experiments involving unconfined compression test, uniaxial tensile test, and matric suction measurement test on expansive soils are performed on two batches of expansive soils. Results show that although no one-to-one relation could be found between UCS and UTS, there is a sound linear relationship between matric suction and the ratio of UCS to UTS. Based on this fact, a two-parameter equation correlating matric suction, UCS, and UTS, was established, and the physical meanings of both parameters are interpreted.