Full scale in situ Engineered Barrier System (EBS) experiments have been addressed in several phases of the DECOVALEX project where water infiltration into the buffer material after the emplacement was analyzed. These experiments demonstrated that the temperature distribution and the water content distribution in the buffer material can be reasonably evaluated by mathematical analysis. However, it is difficult to obtain adequate data on the mechanical behavior of the buffer material, and so further R&D issues remain.

In the full scale in-situ EBS experiment carried out in Horonobe, data acquisition of mechanical behavior (in particular, the swelling pressure of the buffer material) has been undertaken and a good range of high quality data have been acquired. Pressure gauges measure the sum of the swelling pressure, the pore pressure, the thermal expansion, etc., and observations appear consistent with the dry density of the buffer material. However, the Horonobe full scale in-situ EBS experiment includes backfilling of the experimental gallery. It is also therefore necessary to consider interaction between the buffer material and the backfill material accompanied by the resultant buffer and backfill density change. This means that an analysis code needs to consider the change in the dry density of the buffer material and hence more completely characterize the mechanical properties of the buffer. The task being conducted here focuses on the incorporation of such buffer material density changes into the analysis codes.

Experimental Data

The main experimental data comes from the Horonobe full scale in-situ EBS experiment. Over one hundred sensors were be placed in the buffer, backfill and surrounding rock mass during the installation of the experiment to monitor the coupled THM(C) processes, including temperature, pH, lithostatic and pore pressure, water content, resistivity, displacement, and strain. The placement of the sensors was determined from a predictive numerical THM(C) simulation of the experiment.

In addition to this field experiment, there is a large body of thermal, hydraulic and mechanical laboratory scale experiments on the buffer material that will be used to constrain model development in the early part of the task.

Data from a half-sized in-situ EBS experiment which tests infiltration without a thermal gradient is also available, and will be used if required.

Schematic view of the Horonobe full scale in-situ EBS experiment


Step 0 (2020):

The participating teams will improve their analysis code so that they can take into account changes in the dry density of the buffer material.

Step 1 (2020-2021):

Laboratory test results are evaluated; the infiltration test (H process), the swelling pressure test (HM processes), the free swelling test (HM processes), the temperature gradient moisture diffusion test (TH processes).

Step 2 (2021-2022):

The HM processes of an in-situ mockup experiment. In the half sized EBS experiment without heater system, the infiltration process of the buffer material is evaluated. In the backfilled gallery, the infiltration process of the backfill material is evaluated.  (*This step may be skipped)

Step 3 (2022-2023):

The THM processes of the heating period of the EBS experiment including the backfilled gallery and the infiltration period after the heating stop are evaluated.

Participating Groups

  • China: CAS (Chinese Academy of Sciences)
  • Japan: JAEA (Japan Atomic Energy Agency)
  • Korea: KAERI (Korea Atomic Energy Research Institute)
  • Taiwan: Taipower (Taiwan Power Company)
  • Germany: BGR (Bundesanstalt für Geowissenschaften und Rohstoffe) (Step 3)

Further Information

For further information, please contact the task leader, Mr Yutaka Sugita.


  1. M. Nakayama., et al. (2019), The in-situ Experiment for Performance Confirmation of Engineered Barrier System at Horonobe Underground Research Laboratory- Installation of Engineered Barrier System and Backfilling the Test Niche at the 350m Gallery -. JAEA-Research-2019-007 (in Japanese).
  2. M. Nakayama., et al (2019), Collection of Measurement Data from In-situ Experiment for Performance Confirmation of Engineered Barrier System at Horonobe Underground Research Laboratory. JAEA-Data-Code-2019-003 (in Japanese).