This is a discussion piece onSuwal et al. (2025). Salinity and oven-drying effects on the plasticity of a marine soft clay. Géotechnique 75, No. 7, 875–885,Link to the cited article.In this discussion, the discusser has highlighted the need for analysis of the results presented in the paper under discussion, giving due consideration to the effect of the clay mineralogical composition on the plasticity behaviour of Ballina marine clay. The discussion also highlights the previous works documented in the geotechnical engineering literature in the same area.The authors have to be complimented for a detailed presentation of their work on the effects of salinity and oven drying on the plasticity characteristics of Ballina marine clay. Similar and more elaborate works were carried out in India, on Indian marine clays, during the late 1980s and early 1990s (Jose et al., 1988; Rao et al., 1989, 1990, 1992, 1993; Chandrakaran, 1990; Pandian et al., 1991). The discusser feels that it is necessary to examine the paper under discussion in light of those earlier reported research works, which included studies on the effect of salinity, leaching (pore salt extracted, sesquioxides extracted, organic matter extracted) and drying on the plasticity and engineering behaviour of two Indian marine clays, as well as salinised bentonite.Cochin and Mangalore marine clays in the western coastline of the Indian sub-continent, which are characterised by the presence of notable amounts of smectites (42% and 32%, respectively), low to moderate sensitivity percentage (in the range of 1–4), high liquid limits (in the range 75–180%), relatively high natural water contents (varying in the range of 110–150%) and low liquidity indices (< 1), have gained importance owing to their use in the very high level of constructional activities in that region.It is well documented in the geotechnical engineering literature that the behaviour of montmorillonitic soils (i.e. expansive soils) is primarily controlled by factors related to the diffuse double layer (mechanism 1) and the behaviour of kaolinitic soils (i.e. non-expansive soils) is primarily governed by the soil fabric, controlled by the inter-particle attractive forces (mechanism 2) (Sridharan, 1991, 2014). The studies conducted in India have suggested that these mechanisms can be extended to marine soils as well. These observations are also well supported by the studies of Musso et al. (2024).It was noticed that the liquid limits of the Cochin marine clays were mainly controlled by factors related to the diffuse double layer (i.e. mechanism 1), while those of the Mangalore marine clays were primarily governed by the mode of particle arrangement (i.e. mechanism 2) (Chandrakaran, 1990; Rao et al., 1990). These two contrasting controlling mechanisms were mainly attributed to the dominant clay mineralogical compositions of those two marine clays and their response to changes in the chemistry of the pore medium.The results presented in the paper under discussion, which are closely similar to those of the previous works mentioned above, appear to be helpful in further generalising the behaviour of marine clays. In this context, the discusser observed that the paper under discussion has two limitations.A closer look at the results presented in the paper under discussion indicates that the plasticity behaviour of Ballina clay is, perhaps, controlled by mechanism 2 as described above. The discusser opines that a detailed analysis of the results based on the clay mineralogical composition of Ballina marine clay would have thrown much more useful light on determining the mechanism controlling its physical behaviour; this would also help in understanding the dominant mechanisms controlling the behaviour of marine clays in general.A response to this discussion can be found atSuwal et al. (2026). Response to discussion: Salinity and oven-drying effects on the plasticity of a marine soft clay. Géotechnique, Link to the cited article.
Prakash K (Fri,) studied this question.