The analysis of clay soil shrinkage

Abstract

The paper presents the analysis of the capillary and water-colloidal theories of clayey soil shrinkage. The method by which the volumetric shrinkage of the clay soil was determined is that the soil sample is made conical, with an angle at the top of 45-75º, and it is dried in a container geometrically similar to the sample with permeable walls. With kaolinite clays, the shrinkage process has a duration of one week, with hydromicaceous clay of around two weeks, and with montmorillonitic clays three weeks. There is a parabolic dependence between the duration of clay shrinkage and the specific surface area of clay. A series of experiments and calculations have been performed, based on Kulchitsky-Usyarov clay soil model, to determine the limit values of capillary pressure in montmorillonite, hydromicaceous and kaolinite clays using the Laplace formula. At the limit of normal shrinkage, the total porosity for Ca-montmorillonite is 0.45, for Ca-hydromica - 0.25, for Na-kaolinite - 0.385. Calculations showed that during shrinkage the capillary pressure reaches: for Ca-montmorillonite – 48.6 MPa; for Ca-hydromica 8 MPa; for Na-kaolinite - 5.2 MPa. The results obtained practically coincide with the results obtained by K. Terzaghi. Studies on the cyclic “moisture-drying” of clays selected at an experimental site in Ujar (Azerbaijan) showed that after the first “swelling-shrinkage” cycle, with secondary moistening, the swelling of the samples was 12-18 times higher than the primary value.