Abstract

This study focuses on the application of ground source heat pump systems in subway stations, with particular emphasis on the thermal-mechanical coupling response and heat transfer mechanisms of energy slabs. Currently, the thermal performance and structural safety of such structures under actual operating conditions have not been sufficiently investigated.

Based on the Dalian Metro Line 4 project, two sets of in-situ field tests were conducted: one employed a constant inlet water temperature mode to analyze the effects of inlet temperature, flow rate, groundwater conditions, and operation modes on heat exchange performance; the other adopted a constant heating power mode to investigate the influence of heating power and flow rate variations on heat transfer characteristics.

The experimental results indicate that increasing both the inlet temperature and flow rate enhances heat exchange efficiency, with the average heat flux per unit area under intermittent operation reaching 57 W/m², which is 14.7% higher than that under continuous operation. The thermal-mechanical response is significantly influenced by inlet temperature, flow rate, and formation permeability, and a reverse temperature gradient accompanied by an increase in thermally induced compressive stress can be observed during the pump-off phase of intermittent operation.

Uneven flow distribution in heterogeneous soil layers tends to cause localized heat transfer enhancement while reducing overall efficiency. Under long-term operation, the structural response remains within the elastic range, with the maximum thermal stress being 4.15 MPa and the maximum vertical displacement being 2.84 mm, both well below the limits specified in current codes.

This study systematically reveals the working mechanism of energy slabs under multi-field coupling effects, providing theoretical foundations and experimental support for their design and application in thermally activated underground structures.