Investigation of the hydro-mechanical behaviour of GMZ bentonite pellet mixtures
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RESEARCH PAPER
Investigation of the hydro-mechanical behaviour of GMZ bentonite pellet mixtures Zhang-Rong Liu1 • Yu-Jun Cui2 • Wei-Min Ye1,3 • Bao Chen1,3 • Qiong Wang1,4 • Yong-Gui Chen1,3 Received: 23 February 2019 / Accepted: 18 April 2020 Ó Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Bentonite pellet mixtures are considered as one of the candidate sealing materials for deep geological disposals of radioactive waste. One of the particularities of this material is the initial heterogeneous distribution of pellets and porosity within the mixture, leading to complex hydro-mechanical behaviour. In this paper, the hydro-mechanical properties of GMZ bentonite pellet mixtures were investigated in the laboratory by carrying out water retention tests on pellet mixtures under constant-volume condition and single pellets under free swelling condition, as well as a infiltration test on a column specimen of pellet mixture. In the infiltration test, the relative humidity and radial swelling pressure were monitored at five heights, the axial swelling pressure was also recorded. The instantaneous profile method was applied to determine the unsaturated hydraulic conductivities. Results show that, in high suction range ([ 10 MPa) the water retention curve of pellet mixture under constant-volume condition was comparable to that of a single pellet under free swelling condition, while in low suction range (\ 10 MPa) the latter exhibits a much higher water retention capacity. Due to clogging of large pores, the unsaturated hydraulic conductivity decreases as suction decreases to around 25 MPa. However, with further suction decrease, the hydraulic conductivity increases continuously until the value at saturated state, as in the case of most unsaturated soils. The radial swelling pressure at different heights develops with local sudden increase and decrease, which was attributed to local rearrangement of pellets upon wetting. By contrast, as the axial swelling pressure was measured on the global surface of the specimen, it develops in a more regular fashion. Keywords Bentonite pellets Hydraulic conductivity Instantaneous profile method Relative humidity Swelling pressure Water retention
1 Introduction
& Wei-Min Ye [email protected] 1
Department of Geotechnical Engineering, College of Civil Engineering, Tongji University, 1239 Siping Road, Shanghai 200092, China
2
Laboratoire Navier/CERMES, Ecole des Ponts ParisTech, Paris, France
3
Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education, Tongji University, Shanghai 200092, China
4
Institute for Advanced Study, Tongji University, Shanghai 200092, China
Granular mixtures of high-density bentonite pellets are considered as one of the candidate sealing materials for deep underground repository of high-level radioactive waste (HLW), where any openings (deposition galleries, access galleries and shafts, etc.) created during the construction of the repository should be ef
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