Behavior of Laboratory Models of Footing Resting on Layers of Swelling Soil and Sand

Abstract

Expansive clay is one of the most detrimental problematic soils in Egypt in recent years due to the urban expansion in arid and semi-arid areas. During the last few decades, some expansive research efforts were carried out to investigate the geotechnical characteristics of these deposits and the swelling mechanisms of shallow foundations resting on such homogenous formation. However, in situ the soil formations of expansive soil are composed of either thick clay layer, layers of expansive clay inter-layered with seams of non-expansive soil; and mainly sand formation with lumps of expansive soil (6 th of October city, New Cairo city). The objective of this research is study the movement of footing resting on multi-layers of swelling clay and sandusing laboratory model tests. The effect of particles size of sand layers, number of swelling clay layers, activity of swelling clay, and water flow direction are taken into consideration. The final predicted movements of footings are predicted using empirical and semi-empirical equations. Laboratory tests are performed to study the geotechnical characteristics for three grained of sand used in this study and three types of swelling clay used which are classified using direct and indirect measurements tests. The swelling properties are determined using simple modified Oedometer tests. The footing and ground surface heave are measured and predicted for downward and upward water flow. The measured footing and ground surface heave were compared with that predicted values. The used sand types were uniform coarse medium sand, uniform medium fine sand and uniform fine sand. The laboratory model test program consists of four groups. The first group was performed to determine the effect of particles size of sand layers on the movement of footing and ground surface. The second group carried out to determine the effect of No. of swelling clay layers on the movement of footing and ground surface. The third group performed on three type of clay to determine the effect of clay activity on the footing and ground surface movement. The fourth group was deal with water direction to determine the effect of water flow direction on the footing and ground surface movement. The heave movement and moisture content distribution were monitored for different loading cases. The final heave of footing is predicted using semi-empirical heave equation, ) according to Stress Changes methodRama et al., 1988 and Jenning et al., 1973) and two empirical heave equations (according to Seed et al.,1972 and Holtz Gibbs, 1956). The predicted heave values were summarized and compared with those measured in the laboratory model.