Evaluation of an Active System to Measure Lateral Stresses in Unsaturated Soils

A variety of radial stress measuring systems are available in the literature, all of which allow the determination of horizontal stresses with a suitably modified odometer. However, most of the experience with such systems has been on saturated samples. A new osmotic odometer was developed to test unsaturated soils under atmospheric conditions. The device incorporated an active radial stress measuring system to determine the full state of stress during a test. Suction control was achieved by means of an osmotic system, whereas suction measurements were made with miniature tensiometers. The main odometer ring incorporated four small strain-gauged diaphragms, together with a compensating system, to ensure that radial deformations were kept to a minimum. To evaluate the performance of the system, data obtained from a number of tests on compacted clay have been analyzed. Results show that the system yields plausible measurements in the majority of cases; however, there were instances when unusual results were observed. These cast some doubt on the viability of using an odometer equipped with a radial stress measuring system—such as the one presented in the paper—to measure horizontal stresses in unsaturated soils. It is recommended that similar tests are performed with different equipment, to verify whether some of the anomalous results presented in this paper represent actual soil response, or are simply an artifact consequence of the chosen testing method.