Analysis of the influence of different groundwater flow conditions on the thermal response test in Tangshan

Comprehensive thermal conductivity of the rock and soil is generally measured by thermal response test ignoring the effect on groundwater flow. However, the influence of the groundwater flow on thermal conductivity is drastic, so the design of ground heat exchangers with no consideration of groundwater flow is inaccurate. Tangshan is distributed in the river alluvial–proluvial fan of Luanhe River system and groundwater flow rapidly. Hence, analysis of thermal conductivity with thinking about groundwater flow is necessary. In this paper, the comprehensive thermal conductivity within depth of 100 m in Tangshan is measured by two methods: thermal response test and laboratory experiment. Pumping test and tracer test are implemented to simulate of groundwater flow field with different flow conditions. Test results show that: (1) Laboratory experiment results cannot truly represent the comprehensive thermal conductivity of layers. The average thermal conductivity of natural flow field is 23% higher than the laboratory experiment weighted results. (2) The comprehensive thermal conductivity increased 23% with the groundwater flow from the 1.026 to 4.176 m/d. Acceleration of groundwater flow is propitious to improve the thermal conductivity. (3) With the increase in groundwater flow, the initial temperature of ground decreases about 2.3 °C, the results of the stable thermal flow test and the stable operation condition test gradually rise slightly. So acceleration of groundwater flow is conducive to heat exchange. It is proved that the influence of groundwater flow cannot be ignored.