Water retention properties of Boom clay: A comparison between different experimental techniques

The water retention properties of Boom clay samples extracted at a depth of 223 m have been determined in ENPC Paris and UPC Barcelona using different experimental techniques. Boom clay is a stiff clay in which an underground laboratory devoted to carry out research in radioactive waste disposal has been excavated near the city of Mol (Belgium). The retention properties of Boom clay have been investigated for two reasons: i) in good quality samples, a high suction develops in the saturated sample during extraction and its value is correlated with the sampling depth; ii) possible desaturation due to gallery venting during the operational phase may occur in the clay. Various suction control and measurement techniques have been used: osmotic, vapour equilibrium, filter paper, high-range tensiometer and chilled-mirror dew-point psychrometer readings. Some volume changes have also been measured along the equalisation or measuring stages. The values obtained are discussed according to the techniques used. They are compared with previous data on compacted Boom clay samples. The air entry value is estimated close to 4-5 MPa and the shrinkage-swelling properties are also examined. The sample suction at saturation is compared to the in-situ stress state.