| In this study, shear strength and volume change behavior of unsaturated soils is evaluated using axis-translation test methods and advanced testing equipment designed to provide accurate volume change determination during specimen shearing. Tests were performed on a wide range of soil types with net normal stress from 20 to 250 kPa and matric suction from 20 to 700 kPa. This data set adds significantly to the existing database of unsaturated soil properties.; The triaxial test data was analyzed using the extended Mohr-Coulomb equation proposed by Fredlund et al (1978). A hyperbolic curve was fit to the &phis; b versus suction relationship, and a correlation between the hyperbolic curve parameters and soil index properties was developed. Volume change behavior for the soils was related to soil suction, and it was found that for a given suction, the test soils exhibited greater dilation as soil suction was increased. For a given suction, soils exhibited higher compressive strains as the net normal stress was increased, as expected.; A new oedometer device for soil water characteristic curve (SWCC) determination was evaluated by testing a wide range of soil types, and recommendations for best practices for use of this device have been made. The new device allows application of overburden stress to the specimen, measurement of specimen volume change due to suction and overburden pressure changes, and the use of a single specimen for determination of the SWCC. The evaluation includes issues of temperature control, overburden stress, air diffusion through high air entry disks, and a study of potential sources of error in water content determination for SWCC's. It was concluded that the new oedometer device can be used to obtain accurate SWCC determinations on a single specimen up to 1500 kPa. General recommendations for appropriate corrections to SWCC data obtained using axis translation pressure plate-type devices are made. |
