RESEARCH PAPER A method for predicting swelling pressure of compacted bentonites Setianto Samingan Agus Æ Tom Schanz Received: 6 November 2006 / Accepted: 7 February 2008 / Published online: 16 May 2008 Ó Springer-Verlag 2008 Abstract An approach for predicting swelling pressure of bentonites based on thermodynamic relationships between swelling pressure and suction is presented in this paper. The proposed method requires sorption isotherm data of the bentonites. A series of swelling pressure tests were performed on compacted specimens of bentonite-sand mixtures with different bentonite contents, water contents, and dry densities. The sorption isotherm of the pure ben- tonite was measured using a chilled-mirror hygrometer. It is found that the method works well for the bentonite-sand mixtures tested. Several published data on bentonites that have been proposed to be used as buffer and sealing material for nuclear waste repository were collected and used to verify the method. The proposed method is found to be also applicable for other bentonites of different types and therefore, can be used to predict swelling pressure of bentonites. Keywords Bentonite  Sorption isotherm  Suction  Swelling pressure  Thermodynamics 1 Introduction Due to accumulation of hazardous and nuclear waste in interim storage facilities, there is an urgent need to estab- lish final waste repositories in many countries. The current concept, which is adopted in most countries, is to bury the waste contained in a canister in a deep geological forma- tion. The canister (with the waste inside) would be buffered and sealed in the deep geological repository to prevent the waste from being transported to the biosphere in the case of leakage. Compacted bentonite-sand mixtures are among the materials that have been suggested to be used as buffer and sealing element for the deep geological repository concept. This is due to the beneficial properties of ben- tonite-sand mixtures: low permeability, good swelling capability, and good thermal conductivity. In the deep geological repository situations, the materials would be in contact with several liquids. Swelling pressure may develop in the compacted materials when they are in contact with water. Hence, prediction of swelling pressure has become an important topic in the selection of buffer and sealing material for such an application. Several methods have been proposed to predict swelling pressure of clays. Diffuse double layer (DDL) theory, which was earlier suggested to describe the behavior of clay colloid [34], is used to predict swelling pressure and compressibility behavior of compacted clays [19, 26, 31, 33]. Several assumptions used in the approach were com- prehensively described such as in Mitchell [26] and Tripathy et al. [33]. The DDL theory is based on a microscopic physico-chemical concept of clay-water interaction in which a simplified two-clay platelet system is considered. In this model, repulsive forces caused by the overlapping DDLs are the main forces operating in the system. Several other DDL-based theories were also pro- posed, which took into account attractive forces, such as the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory [8, 16, 26, 35, 36]. The computation of swelling pressure using the DDL-based theory requires the knowledge of several physico-chemical properties of the soil. S.S. Agus: Currently, Senior Geotechnical Engineer, Consulting Firm, Singapore. S. S. Agus  T. Schanz (&) Laboratory of Soil Mechanics, Bauhaus-Universita ¨t Weimar, Coudraystrasse 11C, 99421 Weimar, Germany e-mail: tom.schanz@bauing.uni-weimar.de; agus72indo@yahoo.com; tom.schanz@uni-weimar.de 123 Acta Geotechnica (2008) 3:125–137 DOI 10.1007/s11440-008-0057-0