Characteristics of three-dimensional swelling pressure of Gaomiaozi bentonite-sand mixture

The paper presents an experimental and theoretical study of the Gaomiaozi bentonite-sand mixture. The result shows that the three-dimensional swelling pressure increases exponentially with the dry density, and decreases exponentially with the sand content. Anisotropy of swelling pressure is observed in the mixture and the vertical swelling pressure is greater than the horizontal swelling pressure. Both the sand content and dry density affect the anisotropy of the sample. When the sand content is at a lower range, the increase of the sand content has a more obvious impact on the anisotropy. When the sand content is above 30%, the increase of the sand content impacts it less. The anisotropy of the mixture becomes more obvious and gradually stabilized as the dry density increases. Using the index of bentonite dry density based on volume fraction, the three- dimensional swelling pressure empirical model of Gaomiaozi bentonite and its sand mixture has been established, which provided a basis for the buffer/backfilling materials design of deep geological repository of high-level radioactive waste.