In this work, microfocus X-ray computed tomography (渭CT) observations were used in parallel with MIP measurements to further investigate at larger scale the microstructure of a laboratory compacted bentonite/sand disc (65/35% in mass). Qualitative observation of 渭CT images showed that sand grains were inter-connected with some large pores between them that were clearly identified in the bimodal pore distribution obtained from MIP measurements. Due to gravitational and to frictional effects along the specimen periphery, a higher density was observed in the centre of the specimen with bentonite grains more closely compacted together. This porosity heterogeneity was qualitatively estimated by means of image analysis that also allowed the definition of the representative elementary volume. Image analysis also provided an estimation of the large porosity in good agreement with MIP measurements.