On October 13 to 16, 2015, the 8th workshop of DECOVALEX-2015 was held in Wakkanai, Japan. Prof. Pan Pengzhi attended the workshop and gave the reports of three tasks undertaken by Institute of Rock and Soil Mechanics, Chinese Academy of Sciences (CAS research team).

DECOVALEX is the acronyms of DEvelopment of COupled models and their VALidation against EXperiments. It is a unique international research collaboration project, initiated in 1992, for advancing the understanding and mathematical modeling of coupled thermo-hydro-mechanical (THM) and thermo-hydro-mechanical-chemical (THMC) processes in geological systems—subjects of importance for performance assessment of radioactive waste repositories in geological formations. From 1992 up to present (DECOVALEX-2015, on going), the project has made important progress and played a key role in the development of numerical modeling of coupled processes in fractured rocks and buffer/backfill materials. The project has been conducted by research teams supported by a large number of radioactive-waste-management organizations and regulatory authorities, including those of Canada, China, England, Finland, France, Japan, Germany, Spain, Sweden, UK, and the USA, Korea, Czech Republic, etc. Through this project, in-depth knowledge has been gained of coupled THM and THMC processes associated with nuclear waste repositories, as well as numerical simulation models for their quantitative analysis. The on-going DECOVALEX-2015 is chaired by former ISRM president J. A. Hudson and the technical secretary is L. Jing from KTH. DECOVALEX-2015 (from 2012 to 2015) has five tasks, including,

Task A: study of the sealing systems efficiency and the performance of swelling clay-based sealing systems over the long-term at Tournemire underground laboratory in France.

Task B1: understanding of Thermo-Hydro-Mechanical (THM) processes in a bentonite buffer and an argillaceous host rock at Mont Terri rock laboratory in Switzerland.

Task B2: Coupled THM processes in the full scale in-situ engineered barrier system (EBS) experiment at the Horonobe underground research laboratory in Japan.

Task C1: Thermal-Hydraulic-Mechanical-Chemical coupled processes operating within single novaculite and granite fractures

Task C2: study of water flow, tracer transport, and reactive transport in a granite massif, based mainly on the tunnel inflow (flow rate and quality) measured in the Bedrichov Tunnel in the Czech Republic.

CAS research team took part in Task B1, Task B2 and Task C1 of DECOVALEX-2015. On the workshop, Prof. Pan Pengzhi gave three presentations of the three tasks with the titles of Modeling of Mont Terri HE-E Experiment for D-2015 Task B1, Numerical interpretation on EBS experiment of Task B2 and Modeling THMC behavior in novaculite and granite fracture, on behalf of CAS research team.

A self-developed numerical model, i.e. EPCA3D, was used to conduct all the work of Task B1, Task B2 and Task C1 of DECOVALEX-2015. The EPCA3D modeling results were compared with experimental data and the results from other international research teams. The EPCA3D has obtained good improvement and development through the implementation of DECOVALEX project. The research by CAS team can be a good technical support of the study on the associated THMC coupling process of high level radioactive waste disposal, geothermal exploration and CO2 underground sequestration in China.