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Hydro-Thermo-Mechanical Test in a Deep Clay Formation at Mol

Objective

The aim of CACTUS (Characterization of Clay under Thermal Loading for Underground Storage) project is to study the near field thermo-hydro-mechanical couplings in deep clay around a waste emplacement borehole, under thermal loading. This is of major importance for predicting the behaviour of radioactive waste storage, particularly as regards to the irreversible phenomena due to the effect of heating on stresses and pore pressure. The experiment includes two tests conducted in separate boreholes at Mol underground facility, with identical heating probes but different types of thermal loadings and backfilling materials.
The aim of CACTUS project is to study near field thermohydromechanical couplings in deep clay around a borehole waste emplacement, under thermal loading. This is of major importance for predicting the behaviour of radioactive waste storage, particularly with regards to the irreversible phenomena due to the effect of heating on stresses and pore pressure. The experiment is planned to include a number of tests conducted in seperate boreholes at Mol underground facilities, with identical heating probes but different types of thermal loadings and backfilling materials.

The behaviour of the clay under isothermal conditions has been characterized. During the digging of the borehole hydromechanical expansion of the clay was observed, indicated by a drop in pore pressure.

Measurements of water contents and dry specific densities indicate an initial phase in which the clay expands followed by progressive collapse which appears to correspond to the dissipation of the pore pressures.
The heating appears to have caused irreversible deformations of the clay.
Work programme:

1. CACTUS ONE: Emplacing of a prototype heater with backfilling material and heating after hydro-mechanical equilibrium. It is planned as a preliminary test.
2. CACTUS TWO: Emplacing of a heater with backfilling material and earlier heating.

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Coordinator

NATIONAL RADIOACTIVE WASTE MANAGEMENT AGENCY OF FRANCE
Address
Rue Jean Monnet 1-7
92298 Chatenay Malabry
France