The management of clay‐rich soils in agriculture is mainly dependent on their hydromechanical properties that govern their structural evolutions. These structural evolutions are commonly described along the shrinkage curves obtained in a laboratory. Nevertheless, the field survey needs tools of in situ investigations able to characterize the structural profile evolutions of soils through the seasons. This paper presents a method based on the cone penetration and resistivity measurement by penetrometer–salinometer coupling that was gauged in the West Marsh of the French Atlantic Coast. First, the parallel measurements of water and cone resistance (Qd ) profiles in clay dominant soils, characterized by very large ranges of water content (W), allows the calculation of a Perdock's‐type equation that links the Qd profiles and the shrinkage curve of the clay dominant material. Second, thanks to the homogeneity of mineralogy and cationic exchange capacity of the soil, the structure–resistivity relationship was gauged according to the Archie's law taking into account porosity (ϕ), saturation index of the soil (Sat), and the resistivity of the wetting fluid (ρw). The vertical evolutions of structure, resistivity, and cone resistance can be represented in a crossed diagram showing the shrinkage curve–resistivity and Qd profile relationships. Finally, the structural profiles of soils can be modeled from the recorded resistivity and Qd profiles taking into account the ρw

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Although the shrink-swell phenomenon of clays has been thoroughly studied, the in situ relation of the shrinkage curve to the structure profile is rarely presented from the shrinkage limit to the liquid limit. We studied the consolidated structure of clay-dominated (<2 mm) soils formed on 'pseudo-liquid' marsh sediments in the 'Marais de l'Ouest' (France). The profiles were studied in a grassland field and in a sunflower field from unsaturated surface soils down to deeper, saturated, levels characterized by a very large water content (100% by weight). The consolidation states were quantified recording cone resistance (Qd) profiles using a dynamic penetrometer in successive seasons. These Qd profiles were compared with the associated wet density and gravimetric water-content profiles. Two consolidation depths were evident, the surface soil and a 130-cm deep palaeosol. The seasonal Qd profiles demonstrate the partial irreversibility of the consolidation peaks associated with the surface soil and with the palaeosol. The shrinkage properties were established through drying curves of undisturbed test samples. In the void ratio (e)-water content (W) and water content (W)-saturation index (Sr) diagrams, the profiles as a whole exhibit only one clay soil behaviour from their pseudo-liquid to plastic to solid states. Each Qd profile is represented by a hyperbolic curve in the e/Qd diagram. Represented in a (e -W -Qd -Sr) crossed diagram, the vertical evolution of the successive profiles shows the soil structure behaviour from the initial pseudo-liquid sediment to the consolidated soil. A simple cone resistance recording associated with gravimetric water-content profiles, characterizes the evolution of structural layers of soils for the seasonal drying-wetting cycles, for the over-consolidation associated with the palaeosol, and also for the effect of ploughing.

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