Suction effects in deep Boom clay block samples

TL;DR

This study investigates suction effects in deep Boom clay samples, analyzing water retention, swelling, and stress relationships to better understand clay behavior for nuclear waste disposal.

Contribution

It provides new data on suction-stress relationships and the effects of suction release in deep Boom clay, highlighting differences from previous models.

Findings

Suction ratio s/sigma 'v ranges from 0.61 to 1, differing from earlier proposals.

Suction release causes slight swelling of 1.7%.

Sample remains well-preserved with good state of conservation.

Abstract

Extensive investigations have been and are being carried out on a stiff clay from an underground research laboratory located at Mol (Belgium) called Boom clay, in the context of research into deep nuclear waste disposal. Suction effects in deep Boom clay block samples were investigated through the characterisation of the water retention and of the swelling properties of the clay. The data obtained allowed an estimation of the sample initial suction that was reasonably compatible with the in-situ state of stress at a depth of 223 m. The relationship between suction and stress changes during loading and unloading sequences were also examined by running oedometer tests with suction measurements. A rather wide range of the ratio s/sigma 'v (being s the suction and sigma 'v the effective vertical stress) was obtained (0.61 - 1), different from that proposed by Bishop et al; (1974). Finally, the effect of suction release under an isotropic stress close to the estimated sample suction was investigated. A slight swelling (1.7%) was observed and further compression provided a satisfactory value of the overconsolidation ratio confirming the suggestions of taking some precautions before putting a swelling sample in contact with water as suggested by Graham et al. (1987). The various experimental data gathered in this study finally evidenced a relatively good state of conservation of the block sample used.