The variation of bulk density in a vertisol was studied by gamma-ray double bean tomography. Tomographic images of samples deriving from 137Cs and 241Am gamma-radiation were used, providing two attenuation equations which allowed the determination of two variables: bulk density and moisture. The samples, initially with the same bulk density, were submitted to different moistening degrees. The results showed that: (1) the system allowed a satisfactory moisture and bulk density determination; (2) volume of destructured samples varied around 23% from dry to saturated conditions; and (3) the method allowed the analysis of deformed sample expansiveness by the three-straightline method, which allowed to verify the volumetric range during the whole moisture interval and major characteristic points of the soil deformation curve.
bulk density; moisture; swelling and contractions soil; double bean tomography