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 degrees C) on the shear strength (2) the effect of the thermal cycle (20-80-20 degrees 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.