Laboratory Investigations on Extremely High Suction Measurements for Fine-grained Soils

A Dewpoint PotentiaMeter (WP4) was used to measure suction of two fine-grained soils: a locally available silty soil and commercially available white clay, rapidly. Using these results, efforts were made to check the suitability and efficiency of various fitting functions, for defining the soil–water characteristic curve, SWCC, for high suction ranges (0–80 MPa). In addition to this, a knowledge-based database SoilVision 3.34 was used to estimate the SWCC using Pedo-transfer functions, PTFs. The study brings out that the Fredlund et al. [1997, Proceedings of the 3rd Symposium on Unsaturated Soil, Rio de Janeiro, Brazil, pp. 13–23] PTF yields the best estimate of SWCC for fine-grained soils. The influence of the soil type and dry unit weight, on suction and the SWCC fitting parameters, have also been studied.     

Water retention characteristics of swelling clays in different compaction states

The soil–water retention (SWR) characteristics of the clays play an important role in controlling their engineering behaviour, particularly, in the unsaturated state. Although, researchers have attempted to understand the water retention characteristics of the clays in their reconstituted or remoulded state, such studies are rare for the clays in their intact state. In this context, it becomes important to understand the influence of initial state of compaction, which would create different pore and fabric structure (viz., microstructure), on the water retention characteristics of the clays. With this in view, SWR behaviour was experimentally determined for the swelling clays (dried from different compaction states, viz., intact, reconstituted and remoulded) by employing Dewpoint PotentiaMeter (WP4C®). The changes in the pore size distribution of the clays at different stages of drying cycle were also studied by employing the Mercury Intrusion Porosimetry. The study reveals that the SWR curves for the intact and reconstituted specimens of the clays converge beyond a certain stage of drying. Also, a critical analysis of changes in the pore structure of the swelling clay specimens, during drying, indicates that the progressively deforming pore structure plays an important role in controlling its water retention characteristics to a great extent.