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An Approach for Estimating the Shrinkage Geometry Factor at a Moisture Content

Agricultural Engineering Division, Faculty of Civil and Environmental Engineering, Technion, Haifa 32000, Israel

View larger version (24K): [in a new window]   Fig. 1. Scheme explaining Bronswijk's (1988)(1989, 1990, 1991a, 1991b) model of soil layer shrinkage and cracking. (a) Shrinkage of elementary soil cube at initial layer thickness z and volume V = z3 as a result of subsidence z and lateral reduction of initial cube sides to x and y; the volume supplementing the reduced cube [i.e., parallelepiped: x x y x (z – z)] in lateral directions up to volume z x z x (z – z) is interpreted as a crack volume per one initial cube. (b) The initial soil layer composed from unconnected elementary cubes and the layer after shrinkage composed from corresponding parallelepipeds and crack volumes; arrows symbolize the continuation of the three shown cubes to the unlimited layer.

View larger version (20K): [in a new window]   Fig. 2. Scheme of the different shrinkage curves of an aggregated clay soil based on Hallaire's (1984) Fig. 2. (1) Initial specific volume of shrinking and cracking soil layer. (2) Shrinkage curve l of shrinking soil layer with cracks; (3) shrinkage curve s of shrinking soil sample with cracks. (4) Shrinkage curve of soil matrix; in general, z < sz, that is, oven-dried sample contains cracks. (5) 1:1 theoretical line. AB, the specific volume of the layer subsidence at a given w; BD, the specific volume of cracks in the soil layer at a given w; CD, the specific volume of cracks in the soil sample with free boundaries at a given w.

View larger version (23K): [in a new window]   Fig. 3. The general form of the shrinkage curve of a clay matrix [Chertkov's (2000) Fig. 2].

View larger version (25K): [in a new window]   Fig. 4. The experimental specific volume of an unlimited clay layer (asterisks) including cracks, l (field conditions, Bronswijk's approximation when the layer before drying is composed of unconnected anisotropically shrinking cubes), and clay samples (circles) including cracks, s, and the specific volume of a clay matrix without cracks (solid line), predicted from Chertkov (2000)(2003) using data on s, z, and wL (Table 2) for the clay of 0- to 30-cm depths of soil in Sarid, Israel. The inclined straight line is a 1:1 theoretical. Figures near experimental points correspond to the measurement numbers in Tables 3 and 6.

View larger version (27K): [in a new window]   Fig. 5. As in Fig. 4 for the 30- to 60-cm depths, asterisks denote the experimental specific volume of an unlimited clay layer in Bronswijk's approximation, circles denote the experimental specific volume of clay samples with cracks, and the solid line represents the predicted specific volume of a clay matrix without cracks. Figures near experimental points correspond to the measurement numbers in Tables 4, 5, and 7.