Swell–shrink–consolidation behavior of compacted expansive clays

Abstract

The main objective of this study was to develop a clear understanding of the volume change properties of compacted expansive clays. An expansive clay (Gs = 2⋅74 and material finer than 0⋅002 mm = 60%) with a significant water adsorption capacity (wl = 77% and wp = 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 wp. 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 (θ), and degree of saturation (S)) corresponding to drainage through inter-aggregate pores followed by a higher value (100 kPa for w and θ 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.