Foundations on Expansive Soils

Abstract

The preliminary tests and the mineralogical analysis show that TAYBA ELHASANAB and ELHAWATTA soils are highly expansive Soils. These Soils are tested to investigate the effect of the factors affecting the swelling characteristics of expansive clayey soils. The results of these tests show that the increase in the initial moisture content and the decrease in the dry density lead to a decrease in the percentage of swell and swelling pressure of expansive clayey soils. The effect of the surcharge pressure is also investigated, and it has been found that the swelling characteristic can be very much reduced by applying sufficient surcharge pressure. The standard consolidation cell slightly modified to allow for the measurement of the swelling characteristic of soils at different degrees of saturation. This show an increase in the swelling characteristics with the increase of the degree of saturation till they achieve their maximum values at full saturation. The effect of the sample size on the swelling characteristics of soils are detected by using Rowe consolidation cells of 3" & 10" diameters together with the C.B.R mould. The results show that for swelling test , the thickness of the tested sample should be at least one third of the sample diameter to give reliable result. Thus the standard consolidation machine is no longer recommended for carrying out swelling test Undrained triaxial test are used to detect the behaviour of expansive soils, in shear, and when subjected to moisture increase. All the tests in this research are carried out on remoulded soil samples. The different designs of foundations on expansive soils are studied . The experimental research is further extended to investigate the concept of the relief of pressure through voids conducted in the foundations, as a solution to foundation problems on expansive soils. An experimental model is set up which shows that the amount of swell is very much reduced by conducting small voided areas in the foundations.