Pre-compacted blocks of bentonite sand mixture are candidate materials for sealing plugs of radioactive waste disposal. Choice of this material is especially based on its swelling capacity allowing all technological gaps existing between the bentonite based core and the host rock to be sealed. Under real repository conditions, the sealing plugs will start to take water from the host rock and swell. Thereby, a swelling pressure will develop in the radial direction against the host rock and in the axial direction against the concrete confining structures. One important characteristic of this type of heterogeneous mixture is the multimodal nature of its porous network. This multimodal porosity and the highly heterogeneous fabric of the mixture result in a quite complex behaviour during hydration. The paper describes numerical analysis of small scale tests performed on compacted samples of bentonite and sand mixture (70/30 in dry mass). The A coupled HM formulation that incorporates the relevant processes involved in the problem under consideration has been adopted. Technological gaps and heterogeneous structural distribution of the mixture were demonstrated to have an effect on swelling pressure evolution.