Effects of irrigation with brackish water on soil trafficability and workability

The use of brackish water in irrigation practices is a worldwide-recognized problem. The paper aims to relate the well-known alteration effects of salinity and sodicity on soil structure and physical properties to its mechanical behaviour, in order to obtain useful indicators of soil workability and trafficability. The framework chosen for this study is the Critical State Soil Mechanics applied to unsaturated agricultural soil. Four different soils (2 Ustochrepts and 2 Haploxeralfs) were treated at different ESP (Exchangeable Sodium Percentage) and EC (Electrical Conductivity) levels. They were then re-wetted and submitted to partial drying cycles, resulting always in an unsaturated state for the tests. Uniaxial compression and direct shear tests with vertical volume strain measurement were carried out according to Kirby's method. The results have shown significant differences in mechanical behaviour depending on soil type, ESP and EC level and experienced wetting and drying cycles. The outcomes indicate an increase of cohesion values (concerning Coulomb-Mohr's parameters) with increasing ESP but, simultaneously, a displacement of the Critical State Line near the Normal Consolidation line. This would mean an increase of tension states where the soil expands at failure by shear. The outcomes of this work constitute a basis for developing further research work, in order to relate them with trafficability and workability indications.