Shear strengths and volume changes of sand–attapulgite clay mixtures

Compacted sand–expansive clay mixture with low hydraulic conductivity and appropriate shear strength is employed as liner systems for waste containment systems to prevent groundwater contamination by leachate from the waste. The aim of this study was to assess the shear strength behavior and swelling potentials of sand–attapulgite clay mixtures. The attapulgite clay used in this study was obtained from the eastern province of Saudi Arabia and was characterized as highly expansive. A detailed experimental program was devised to evaluate the effects of clay content (ranging between 0 and 60 %), initial molding conditions (optimum and wet-of-optimum), normal stress, and wetting conditions (as-compacted and inundated) on shear strength behavior. Also, the effects of clay content and initial molding conditions on the swelling potential of the mixture were evaluated. Test results revealed different trends for the shear stress–strain curves, signifying that different structural arrangements resulted from the use of different clay contents and molding conditions. Furthermore, test results identified an optimum clay content of 30 % which yielded the maximum shear strength; beyond this, a significant reduction in the shear strength of the sand–attapulgite clay mixture was observed. Finally, the shear strengths of sand–attapulgite clay mixtures were compared to those of sand–bentonite mixtures.