Water retention parameters and sediment dispersivity of the Zemun loess plateau (Belgrade, Serbia)

Abstract

The paper presents the results of recent investigations of the Zemun Loess Plateau, which focused on unsaturated and dispersive loess soil. Soil water retention curves, SWRCs, were determined experimentally, using a pressure plate apparatus for suction values of up to 1500 kPa, according to ASTM(1). Soil dispersivity was determined by means of the double hydrometer test, crumb test and pinhole test according to BS2 and ASTM1. The tests were carried out on samples of loess soil with different grain-size distributions, as well as natural and artificially prepared samples with different degree of compaction. The results of the study confirm that an indirect correlation can be established between SWRC parameters and soil dispersivity. Soil dispersivity increased with increasing soil entry values (u(a) - u(w))(b) and the residual degree of saturation S-res, and decreased with decreasing coefficient lambda. The air entry value and residual degree of saturation increased and the desaturation rate decreased with increasing proportions of the clay-size fraction. Soil compaction appears to have a greater effect on SWRC parameters than on soil dispersivity. The air entry value increased, but coefficient lambda. decreased with increasing density. Loess soil dispersivity tends to depend more on the chemical and mineral composition. Soils with more sodium and clay minerals are more dispersive.