Shear strength and compression behavior of colemanite-added sand-bentonite mixtures under high temperature and temperature cycles

Soils surrounding energy geo-structures are exposed to high temperature and temperature cycles. Such thermal changes may affect the engineering behavior of soils negatively. It is very important that the soils around energy geo-structures maintain its engineering parameters unchanged for a long time under thermal changes. Understanding how barrier is affected when exposed to high temperature is crucial for the long-term performance of the barrier. The aim of study is to keep the soils around the energy geo-structures such as nuclear waste disposal facilities, maintain their engineering characters without failure for a long time under high temperatures and thermal changes. In the present study, sand-bentonite mixtures, which are widely used as a barrier material, and colemanite, one of the boron minerals known for its thermal strength, were used. An experimental study investigated (1) the effect of high temperature (80 °C) on the shear strength (2) the effect of the thermal cycle (20-80-20 °C) on compression of additive free sand-bentonite mixtures and colemanite added sand-bentonite mixtures. The laboratory tests were performed in a temperature-controlled modified shear box and oedometer cell. Based on the results obtained, colemanite additive contributed to the improvement of shear strength of sand-bentonite mixtures at high temperature. However, colemanite addition increased the compression amount and thermal cycling effect reduced the compression index.