Abstract: To study the effect of temperature and water pressure on heat and mass transfer in buffer material, taking the compacted Gaomiaozi bentonite as an example, coupled thermo-hydro equations are derived from potential-based control equations of unsaturated soil, with the consideration of evaporation. We modify the smoothed particle hydrodynamics (SPH) algorithm to get coupled solutions with varying parameters during the calculation. Parameters of each single representation elementary volume will be updated in real time according to the current state. Results indicate that: Because calculation parameters are closely related to soil’s state, variation of parameters influence significantly on the results. The heat from nuclear waste can spread through the buffer in a short time, water migration rate is relatively slower. Increasing of buffer’s temperature will accelerate the migration of water. In comparison, water pressure has smaller effect on temperature distribution.

Key words: buffer material, unsaturated soil, thermo-hydro coupling, smoothed particle hydrodynamics (SPH) algorithm