Numerical simulation study on thermal performance of energy piles in coastal soft soil

The thermal performance of energy piles in coastal soft soil was investigated. Based on the modified Cambridge model， the energy equation， and the momentum conservation equation， a three-dimensional multi-physics field coupling finite element model for single piles and pile groups was developed. The effects of heat exchange pipe arrangement， pipe wall thickness， ground temperature， and pile top load on the thermal performance of energy piles and surrounding soil were systematically analyzed. The results indicated that： （1） When the branch pipe spacing for single piles and pile groups was within the range of 100 to 200 mm， the unit heat exchange rate increased significantly； However， when it exceeded 200 mm， the growth rate diminished； （2） As the pipe wall thickness increased， the heat exchange rate of single piles and pile groups decreased markedly， with the reduction rate slowing down when the thickness exceeded 4 mm； （3） The settlement change of single piles before and after pile top loading was 0.07 mm， while for pile groups， it was 0.027 mm， suggesting that single piles exhibited a more pronounced settlement response to load variations； （4） For both single piles and pile groups， the faster the flow rate of the circulating medium， the lower the heat extraction efficiency； When the flow rate exceeded 0.4 m/s， the decrease in heat extraction efficiency slowed down. The results elucidated the mechanisms underlying the changes in thermal performance of coastal soft soil energy pile systems， providing a theoretical foundation for the design， material selection， and construction control of coastal geothermal energy pile foundation engineering.