The hydraulic conductivity of aggregated clay soils under loading, leaching and reclamation

Naseri, Abd Ali (1998) The hydraulic conductivity of aggregated clay soils under loading, leaching and reclamation. University of Southampton, Doctoral Thesis.

Abstract

Investigation into the literature has shown a lack of research into the effect of leaching on the physical and chemical properties of restructured saline-sodic clay soils. Studies have therefore been performed in order to provide a better understanding of the behaviour of saline-sodic clays after restructuring and during leaching.

For this study, a permeameter was designed and tested. The permeameter and method are functional.

Experiment on the impact of the overburden weight on hydraulic conductivity indicates that as the overburden weight increases hydraulic conductivity and macroporosity of aggregated clay decreases dramatically. One important result of the experiments was to establish the relationship between hydraulic conductivity and macroporosity for restructured clay soil.

Experimental measurement of the effect of leaching water quality on saline sodic soils during leaching indicated that extensive swelling occurred when low salinity water was used. It is also clear that swelling for a particular initial sodicity increased as the salinity of the leaching solution decreased. It is clear that swelling of saline sodic clays can be controlled if leaching is combined with reclamation. This is possible by using water of moderate salinity and low SAR to leach the soil. By controlling the swelling of shear strength of the soil can be maximised to resist the stresses developed due to overburden weight during leaching and reclamation.

Another experiment was conducted to observe the effect of swelling on the soil macroporosity and hydraulic conductivity during leaching. In this experiment, in one treatment a non-sodic saline clay (EC=20 dS/m, SAR=2) was leached with water of EC=0.5 dS/m, SAR=0.59. As expected, structural instability and loss of hydraulic conductivity did not occur during leaching this soil. However, when a saline sodic clay (EC=20 dS/m, SAR=40) was subjected to leaching with the same water, as expected, the soil structure was completely destroyed and the hydraulic conductivity declined dramatically. However, in treatments in which calcium amendment was used it became clear that increasing the calcium concentration in the leaching water can prevent the saline sodic clays from structural instability and loss of hydraulic conductivity.

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