Based on a lab-scale setup, the thermal and flow performances of a single spiral-tube ground heat exchanger under certain operation mode (6 h on and 18 h off) were examined in terms of the influence of Reynolds number (3000-8000) and backfill materials (native sand, and sand/kaolin blend with 5% adding ratio of kaolin). The convective heat transfer coefficients for the tube buried in the blend were between 370 and 678 W/m(2) K, which were higher than those in the sand. Also, the effectiveness of the heat exchanger in the blend was higher than that in the sand. The average values of the temperature restoration degree in the sand backfill and surrounding soil field after 18h off increased by about 18-25%, compared to those after 6 h on, while that in the blend backfill and surrounding soil field increased by about 36-42%. It is an available option to add the kaolin into the sand for enhancing thermal performance of the ground heat exchanger. The intermittent operation mode should be also a feasible technique for prompting the thermal performance of the ground heat exchanger. (C) 2019 Elsevier B.V. All rights reserved.