Abstract
Thermal changes affect the engineering behavior of surrounding soils at energy geostructures. For that reason, there is a need for durable soils which are not affected from high temperatures or thermal cycles. Such soil mixtures can be developed by adding temperature-resistant materials such as perlite to the sand–bentonite mixtures. In this study, 10 and 20% perlite additives were added to 10 and 20% sand–bentonite mixtures, in order to develop durable soil mixture under high temperatures. Direct shear and hydraulic conductivity tests were performed under room temperature and high temperatures. The results of the experiments showed that the perlite additive reduced the dry unit weight of the sand–bentonite mixtures and had a positive effect on the shear strength of 20B–80S mixtures both under room and high temperatures. The perlite addition increased the angle of internal friction of sand–bentonite mixtures under room and high temperatures especially for 20% bentonite–80% sand (20B–80S) mixtures. The hydraulic conductivity (k) values of both mixtures increased with increasing temperature. As a results of thermal cycles, it was seen that the samples cannot turn back to their initial k values.
Highlights
Temperature increase and thermal cycles occur in the surrounding soils at energy geostructures such as; gas pipelines, geothermal power plants, buried power cables, energy piles, solid waste and nuclear waste storage areas
When the perlite percentage in the mixture was increased from 10–20%, the maximum dry unit weight decreased to 13.1 kN/m3 and the wopt reached to 30%
The results showed that the thermal conductivity values decreased as the perlite was added to the sand-bentonite mixtures (Table 5)
Summary
Temperature increase and thermal cycles occur in the surrounding soils at energy geostructures such as; gas pipelines, geothermal power plants, buried power cables, energy piles, solid waste and nuclear waste storage areas. Cekerevac and Laloui (2004) investigated the shear strength behavior of kaolin clay by increasing the temperature from 22°C to 90°C. In the opposite direction another finding reported that; the triaxial compression tests on the Pontida silty clay have shown that shear strength decreased when temperature increased from 18°C to 115°C (Hueckel and Baldi 1990). According to the unconsolidated-undrained (UU) and consolidated-undrained (CU) test results for Boom clay, a significant decrease in strength was determined when the temperature increased. It was reported that when soil is heated, all components of soil expand If this soil is a clay group, this expansion results change in the distance between the clay particles and a decrease in the strength of the adsorbed layers (Fleureau, 1979; Robinet et al 1996). It was determined that the elastic modulus increases and preconsolidation pressure decreases when soil is heated (Cekerevac and Laloui 2004)
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