Helical filter paper technique for uniform distribution of injected moisture in unsaturated triaxial specimens

The field stress path experienced by a soil element during rain-induced slope failures is reproduced by injecting water in an initially unsaturated specimen under constant total stress conditions. The accumulation of injected moisture near the base of triaxial specimens causes non-uniformity in the specimen leading to progressive failure. A new idea of using a helix shaped filter paper wrapped around the specimen’s periphery to uniformly distribute the injected water is presented. Water injection experiments were conducted and the behavior of specimens with and without the presence of filter paper was compared under constant shear stress. The use of helical filter paper ensured more uniform distribution of injected moisture, and reduced the discrepancy of moisture along specimen’s height by around 50%. Improvement in moisture uniformity of the specimen also reduced the possibilities of progressive failure during water injection experiments. The helical filter paper technique was found to hold a strong potential for the reproduction of rain-induced landslide conditions in laboratory triaxial experiments.