Monitoring and analysis of the subway tunnel wall temperature and surrounding rock/soil heat absorption ratio

Abstract The subway tunnel wall temperature (STWT) and surrounding rock/soil heat absorption ratio (SHAR) have significant effects on both the thermal environment and energy consumption in subways. However, the complexity of subways and their influencing factors make using simulations for real situations both difficult and inefficient. In-situ monitoring experiments are more effective for characterizing real situations in subway tunnels by comparison. In this study, in-situ monitoring of the STWT, tunnel air temperature and wall heat flow in a typical interval tunnel of Nanjing subway was conducted for 68 days in the summer. The results indicate that the running of the train, tunnel air temperature and surrounding rock/soil temperature were the three main factors affecting the STWT and heat flow in the subway tunnel. A simplified analytical solution for the STWT that considers these three factors was proposed using the Green's function method. The proposed analytical solution was validated by the in-situ monitoring data. Based on the actual information of the subway train, the total heat remaining in the tunnel by a train passing through was approximately 42.5 MJ, and the SHAR was between 8.6% and 30.6% during different periods. The results of this study not only provide a formalism that could be used as an alternative to complex and time-consuming simulations for predicting the STWT, but they also provide references for how the design and operation of new energy utilization systems could be optimized by estimating the value of the SHAR based on in-situ data.