As part of the Hades Project ANDRA developed the Cactus project (Characterisation of Clay under Thermal loading for Underground Storage) for the purpose of in situ study of the thermo-hydro-mechanical behaviour of a clay massif in the near field of a heater to simulate the thermal release of a stack of vitrified waste packages after 50 years of cooling.
In previous tests, CACTUS 1 and CACTUS 2, particular care was taken to ensure accurate tracing of the clay response and reliable measurements. Peripheral instrumentation for each test included thermal probes (temperature), piezometric nests (pore water pressure), Glötzl cells (total stress), extensometers (strain) and a gamma-neutron probe (clay density and water content).
This instrumentation enables the evolution of the principal physical parameters of the clay massif to be monitored closely throughout all tests, each of which had three phases corresponding to specific thermo-hydro-mechanical loads:
(1) Excavation of the borehole
(2) Installation of the heater and consolidation of the clay massif around the borehole
(3) Heating/cooling cycles
The CACTUS tests constitute a rather unique and comprehensive experimental data base that facilitates the overall conduct of modelling from the isothermal phases through thermal cycling. Based on this, ANDRA set up two research teams, that started out with different approaches to the thermo-hydro-mechanical behaviour of the saturated clays, particularly Boom clay, and with different modelling tools to conduct the CACTUS tests:
(a) The G3S Research Group on Underground Structures (France)
(b) The ISMES (Italy)
The programme of the study is structured according to following tasks:
B.1 Collection and compilation of the data and characterisation of the Boom clay. Review of the in situ (thermo)-(hydro)-mechanical tests at Mol. Preparation of the modelling.
B.2 Modelling of a CACTUS test
B.3 Analysis and synthesis of the modelling results
Funding SchemeCSC - Cost-sharing contracts