Characteristics of Scanning Curves of Two Soils

Abstract

Scanning curves of two different soils were obtained from three series of infiltration and drainage experiments on two physical models of soil slopes in the laboratory. The first slope model consisted of a fine sand layer overlying a gravelly sand layer, while the second slope model involved a silty sand layer overlying a gravelly sand layer. Each soil layer had a thickness of 200 mm and both slope models had an inclination angle of 30°. The slope models were subjected to artificial rainfalls of different intensities, followed by draining where no rainfall was applied. Various instruments were installed to continuously measure the changes in matric suction, volumetric water content and the water balance of the slope models during the experiment. Scanning curves were then constructed using the matric suction and water content data measured at the bottom, middle and top parts of the slope models and were compared with the primary drying and primary wetting soil-water characteristic curves that were measured separately. It was found that the scanning curves followed the primary wetting curve during the adsorption process and then followed the primary drying curve during the desorption process. During the transition period, over which the scanning curve moved from the primary drying curve to the primary wetting curve (or vice versa), the path of the scanning curve had a relatively flat slope as compared to the slope of the primary curves, and sometimes it was almost horizontal. However, the slope and the path of the scanning curves were found to be similar for the cases with similar initial conditions.