Fig. 2. Schematic representation of (a) the volumetric shrinkage of the unitary prism (a = prism side dimension, h = prism height dimension, a and h = decrease of prism dimensions), and (b) crack opening (horizontal shrinkage) and subsidence (vertical shrinkage) phenomenon in the grassland field. Layer 1 = solid state (W [gravimetric water content] < W_p [plasticity limit]), crack opening and subsidence operate simultaneously. Layer 2 = plastic to "pseudo liquid" state (W > W_p), only subsidence operates (_b = wet density of the clayey matrix, = microporosity of the clayey matrix, fracture area = horizontal shrinkage (cracks) at the soil surface, a^1/3 = calculated aperture of crack, WSTS = wet season topographic surface, DSTS = dry season topographic surface).