Visualization of thermal interference effects in energy piles using transparent soil

Thermal interference between adjacent energy piles in group configurations can significantly reduce system efficiency. Conventional temperature monitoring methods rely on discrete sensors, which fail to capture the continuous spatial evolution of soil temperature fields. This study developed a non-contact visualization method for temperature fields based on transparent soil and digital image processing technology to investigate the thermal interference effects surrounding energy piles. The transparent soil was composed of fused quartz sand and a refractive index-matched pore fluid (mineral oil and dodecane at a mass ratio of 4:1). By calibrating the functional relationship between normalized pixel intensity and temperature, non-contact measurement of the soil temperature field was achieved. The temperature distributions under single pile and double pile conditions with different pile spacings (2–6 times pile diameter D ) were investigated, and a thermal interference coefficient was introduced to quantify the thermal interaction between piles. The results indicate that when the pile spacing is within 4 D , variations in spacing have a significant impact on the thermal interference effect. When the spacing increases to 6 D , the thermal interference coefficient decreases to 2.5%. The proposed visualization technique successfully reveals the spatial pattern of thermal interference and provides quantitative references for energy pile group design. Limitations regarding scale effects, thermal property mismatch, cyclic loading, 3D heat transfer, calibration uncertainty, and groundwater advection are discussed to guide future research.