Novel system for rapid soil thermal conductivity with constrained environmental conditions

Accurate measurement of soil thermal conductivity (k) is essential for the design and safety of underground infrastructure, including buried power cables, ground-source heat pump systems, and pipelines. Conventional transient line heat source (TLHS) methods are widely used but operate under open boundary conditions, exposing soil samples to moisture evaporation, ambient temperature fluctuations, and uncontrolled heat exchange. These disturbances inflate measured k values and reduce repeatability, especially under variable moisture and salinity conditions. To address these limitations, this study proposes the Environmental-Controlled Thermal Conductivity (ECTC) system as a novel approach for soil thermal conductivity measurements under more constrained environmental conditions that eliminate heat- and moisture-loss and open-boundary disturbances in addition to accelerating the tests with sample removal and replacement, while preserving the established TLHS measurement principle. Experimental validation was performed on compacted ASTM C-33 fine sandy soil across three salinity levels (non-saline, moderate, and high) and six moisture contents spanning dry to in-situ conditions. The ECTC system consistently produced k values within the physically expected range for more in-situ compacted sandy soils (0.32–3.11 W/mK), whereas the conventional “open-boundary” approach yielded anomalously high peak values exceeding 4.87 W/mK, which is more than 50% above reported literature maxima. The ECTC system reduced total test durations by approximately 30% (mean: 2,292 s vs. 2,768 s; paired t-test: t = − 7.63, p = 0.017) and lowered measurement variability by up to 56% under moderate salinity conditions. The system also resolved a physically realistic non-linear salinity response, a k enhancement at moderate ionic concentration and a plateau at high salinity, which the conventional method failed to capture. These results demonstrate that the ECTC system can deliver superior accuracy, repeatability, and sensitivity to multi-factor environmental conditions compared to the conventional testing approach. The findings herein establish the ECTC system as a reliable and efficient alternative for soil thermal conductivity measurement, with direct implications for underground cable ampacity design, geothermal borehole sizing, and pipeline thermal management in saline or variable-moisture soil environments.