THE RELATIONSHIP BETWEEN SUCTION AND SWELLING PROPERTIES IN A HEAVILYCOMPACTED UNSATURATED CLAY

In order to study the hydro-mechanical behaviour of highly compacted u nsaturated clays used in engineered clay barriers for nuclear waste di sposal, some experimental techniques for controlling suction were exte nded into the range of high suctions. The technique of control by impo sing a given relative humidity was considered for very high suctions ( several hundreds of MPa), and calibration data from the literature wer e examined. Some corrected values were proposed, based on a calibratio n made with sodium chloride. The extension of the osmotic technique to higher suctions was made, and a value of 10 MPa was attained, enlargi ng considerably the range of this method. The study of the water reten tion and swelling properties of the FoCa7 clay under controlled suctio n and zero applied stress is presented. A good continuity between the two methods of suction control was observed. Fairly reversible respons es to suction cycles were observed, in terms of water content and volu me change. During these changes, it was observed that the air volume r emained constant. The reversibility is related to the predominant role of a saturated microstructural level, strongly influenced by the phys ico-chemical bonds existing between water and the active clay minerals . (C) 1998 Elsevier Science B.V. All rights reserved.