Evaluation on structural integrity of energy slab using thermo-hydro-mechanical coupled numerical model

Energy slabs utilize geothermal energy by incorporating heat exchange pipes within the building's concrete slabs. The periodic temperature fluctuations in these pipes caused by the operation of a ground source heat pump system led to thermal expansion or contraction of the concrete slab (i.e., thermally induced stress), potentially adversely affecting the structural integrity of the building. To address this, a thermo-hydraulic-mechanical (THM) numerical model was developed to thoroughly assess the structural integrity of energy slabs. First, the energy slab was installed in the underground parking lot of a residential building, and thermal performance tests (TPT) were conducted. Based on the tests, a numerical model of the energy slab, capable of accurately simulating the THM behavior observed during the TPTs, was developed. Subsequently, both short-term and long-term analyses using the numerical model were conducted to evaluate the THM behavior of the energy slab. The results indicated that the maximum stress of 9,303 kPa was caused by the long-term cooling operation of the energy slab, highlighting that the expected maximum thermally induced stress in response to the temperature changes in the circulating water and strain restriction of the energy slab should be considered when designing energy slabs.