Swell-shrink-consolidation behavior of compacted expansive clays

The main objective of this study was to develop a clear understanding of the volume change properties of compacted expansive clays. An expansive clay (G(s)=2.74 and material finer than 0.002 mm=60%) with a significant water adsorption capacity (w(l)=77% and w(p)=27%) was used. The maximum dry density was found to be 1.45 g cm(-3) at the optimum water content of 26% which is close to w(p). The soil water characteristics curve exhibited two air entry values for all of the index properties: a lower value (10 kPa for gravimetric water content (w), volumetric water content (h), and degree of saturation (S)) corresponding to drainage through inter-aggregate pores followed by a higher value (100 kPa for w and theta but 6000 kPa for S) associated with seepage through the soil matrix. The shrinkage path during progressive drying of the investigated expansive clay exhibited an S-shaped curve with three distinct portions: an initial low structural shrinkage (S=100% to S=85%) followed by a sharp decline during normal shrinkage (S=85% to S=75%) and then by a low decrease during residual shrinkage (S=75% to S=0). The swelling potential and swelling pressure curves were also S-shaped with the following swelling stages: slow initial swelling because of the low unsaturated hydraulic conductivity; rapid primary swelling due to an established wetting front; and low secondary swelling owing to near saturation conditions. The swelling potential measured 10% and the corrected swelling pressure was found to be 290 kPa. Likewise, the compression index and the swell index were found to be 0.17 and 0.09, respectively. The predicted heave for a 1 m thick clay was found to range between 70 mm and 90 mm.