Work Package 4 is focussed on the simulation of Thermal-Hydro-Mechanical (THM) and Chemical processes in clay buffers and host rock in order to improve the understanding of these processes for radioactive waste disposal safety cases. Three benchmark cases based on THM laboratory experiments are being modelled in the present phase of the project. For example, the following figure shows a comparison of Quintessa's modelling results using the QPAC multi-physics code with experimental data for the time-dependent relative humidity and temperature in resaturating bentonite.