GEOTECH N I CA L PROPERTIES OF SOME SWELLING DEPOSITS IN NEW COMMUN ITIES AROUND THE GREATER CAIRO

Abstract

Expansi ve soils have been considered the most detrimental problematic deposits in Egypt. During the last few decades some extensi ve research efforts a nd attempts were ca rried out to simplify the identification and cl assification of different expansi ve deposits and to investi gate the swelling mecha nisms of different foundations resting on these soi ls. The main a im ofthis thesis is to examine the analytical heave pred iction methods for calculating swelling movements in some of the new commun ities in Egypt. TI1e swelling cha racteristics were determined for expansive deposits at three new communities around the Greater Cairo; El-Obour, El-Mokattam, and EI-Qattamiya, as representative examples for the geologica l formation and geotechnical properties of this region. The three new cities are considered the northeast extension of the new communities around the Greater Cairo. The expansive soils at the selected sites in the three cities are classified as hi gh to very high swelling clays. The ground surface heave was predi cted ana l ytically using different approaches; semi-empirica l methods as suggested by two different procedures (Stress Changes and Suction Changes) as well as the empirical methods empl oying heave equations. Effects of the magnitude of active depths and the thickness of non-expansive soil overlying the expansive clay l ayer on the expected heave values are investigated in a parametric study for the three new cities. The methods were also used to evaluate the contribution of soil replacement to damping of heave movements. The predicted heave values using these methods are compared with that measured in large-scale laboratory tests. The comparison revealed that the empirical heave method, suggested by Brackley, et al. (1983), is the best method for heave prediction. The results also showed that optimum treatment of expansive deposits using soil replacement with adequately compacted sand can be achieved when the thickness of compacted sand is about 40% of the active depth.