A study of tensile stress with suction by restrained ring method

In expansive soils, tensile strength and tensile stress are two main factors that control the development of cracks due to drying shrinkage. Numerous experimental methods and theoretical models have been proposed for the measurement and prediction of tensile strength. However, there are only few studies that focus on the measurement and prediction of tensile stresses in expansive soils. Understanding the mechanism behind the crack initiation due to an increase in suction in expansive soils is of paramount importance in geotechnical engineering. In this study, the restrained ring method was modified for studying the variation of tensile stress with suction. Strain gauges were installed in the restrained ring to measure tensile strain, and a tensiometer and filter paper method were utilized to measure the suction. The experimental test results indicate that the change of tensile tress with suction can be generally simulated by the model proposed by Chen and Bulut (2017). It is noted that tensile stress increases nearly linearly with suction expressed in pF units (i.e., suction in logarithmic scale, pF = log(10) (suction in cm of water as a positive number). Soil suction is also currently represented in log(10) (kPa) unit system (i.e., log(10) (kPa) = log(10) (suction in kPa units as a positive number). In addition, it is found that the maximum tensile stress measured from the specimens initially at optimum water content is approximately twice the value of the maximum tensile stress measured from the specimens at near-saturation state. The test results also indicate that the suction change from the initial moisture state to crack initiation is about 0.2-0.3 pF for the specimens at optimum water content, and is about 0.5-0.7 pF for the specimens at near-saturation moisture state.