Experimental investigations on thermo-hydro-mechanical properties of compacted GMZ01 bentonite-sand mixture using as buffer materials

• Sand content can inhibit the maximum swelling pressure of sand-bentonite mixture effectively.
• The hydraulic conductivity of the mixture increased with increasing sand content.
• The increase of sand content could induce significant increase of thermal conductivity of the mixture.
• Sand content in the mixture should not be more than 30% in view point of THM properties.

Bentonite-sand mixture has been proposed as engineered barriers for high-level waste disposal in many countries. For investigation of the thermo-hydro-mechanical properties of compacted GMZ01 bentonite-sand mixture, swelling pressure, hydraulic and thermal conductivity tests were conducted in this paper. Results show that addition of sand will increase the thermal conductivity of the mixture. However, depending on the dry density and water content of the specimen, the increasing rate of thermal conductivity becomes stable or even decreases with further increase of sand content. The addition of sand will also impede the development of swelling pressure while the inhibiting effect becomes weak as the sand content increases. In the meantime, with increasing sand content, the hydraulic conductivity of the mixture will increase significantly, especially at higher sand contents. Analysis shows that, sand content should be kept below 38% and 39% to guarantee the swelling pressure above 1.0 MPa and the hydraulic conductivity lower than 1.0e − 12 m/s, respectively. The most effective sand content in the view of heat dissipation of buffer materials is < 30%. Therefore, the preferential option of sand content in the mixture should not be > 30% in view point of thermal-hydro-mechanical properties.