Matric Suction Measurement of Unsaturated Soils With Null-Type Axis-Translation Technique

Matric suctions of several compacted soil specimens of a low-plastic soil were measured using null-type axis-translation technique. The study showed that in general, the dynamically compacted specimens reached equilibrium sooner than the statically compacted specimens and exhibited greater matric suctions. For a given compaction type (dynamic or static), the influence of an increase in the dry density due to an increase in the compaction effort had practically negligible influence on the measured matric suctions. Comparison of the null-type test results with the suction-water content soil-water characteristic curves of the soil showed some disagreements particularly for matric suctions greater than 20 to 30 kPa. Continuity in the water phase between the soil water, the water in the ceramic disk, and the water in the compartment below the ceramic disk, was verified soon after the measurements of matric suction were completed by increasing the chamber air pressure and monitoring the corresponding water pressure increase below the ceramic disk. The test results clearly showed a lack of continuity in the water phase during the suction measurements. Use of various interface materials (viz., a wet filter paper, slurries prepared from the tested soil and a kaolinite) significantly improved the water phase continuity; however, reduced the matric suctions of the soil specimens tested.