Pressures Needed to Suppress Expansion in Clayey Soils

It is quite often geotechnical engineers suggest the use of concentrated loads in order to suppress the swelling under foundation for areas known of expansion. The swelling pressure obtained using constant volume apparatus and/or oedometers are certainly not simulating actual field conditions. The minimum applied dead load suggested based on these tests may be too high and may be associated with excessive settlement or exceeds the bearing capacity of the substrata. The difference between bearing capacity and minimum dead load required to suppress expansion can be very small. In this case careful computations for the settlement and swelling pressure shall be performed. A site in Khartoum showed typical problem and the choice of the appropriate geotechnical design parameters were to be studied. Seventeen boreholes were drilled in order to ascertain the subsurface condition and its ability to sustain infrastructure facilities. Swelling pressure obtained in a constant volume or oedometer in a constrained testing shall be corrected based on actual relaxation that occurs in the field due to immediate and/or consolidation settlement. A methodology for evaluating short and long term settlement was conducted to predict the downward movement of the substrata during the lifetime of the proposed structures. The design of the foundation system in such soil should exert downward loads greater than the corrected swelling pressure and without causing excessive settlement beyond the permissible limits.