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.% 对不同干密度和含砂率高庙子膨润土–砂混合缓冲/回填材料的试样进行一系列三向膨胀力试验研究，结果表明，混合料三向膨胀力均随干密度呈指数关系递增，随含砂率呈指数关系递减。混合料存在各向异性，竖向膨胀力大于水平向膨胀力；含砂率和干密度均对试样的各向异性产生影响；当含砂率大于30%以后，含砂率的增加对其各向异性影响较小；混合料的各向异性随干密度的增大更加显著，并逐渐趋于稳定；对各向异性的机制进行分析，提出基于体积率的膨润土干密度这一指标，建立高庙子膨润土及其含砂混合料三向膨胀力的经验模型，并对模型进行验证和应用，研究成果可为高放废物深地质处置库中的缓冲/回填材料设计提供参考。
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