A novel method to study the energy conversion and utilization in artificial ground freezing

Highlights: • A novel method to evaluate the energy conversion efficiency of AGF project. • Quantitative indicators for energy conversion and utilization in AGF is proposed. • Developed model considers thermal-mechanical coupling and ice-water phrase change. • EUR curve is obtained based on different types of energy indices calculated. The artificial ground freezing (AGF) method is widely used for soil reinforcement in underground engineering. The AGF method has been confirmed very effective, however, it consumes a great deal of energy during construction. Therefore, it is of great significance to study its energy conversion and utilization, which is very important for better and more energy-efficient employment of this method. In this paper, a novel method, which could effectively calculate the energy utilization rate (EUR), is proposed to evaluate the energy conversion efficiency of a typical AGF project. First of all, the brine temperature and ground temperature are monitored and analyzed. Secondly, according to the monitored data and actual layout of freezing pipes, a sophisticated three-dimensional solid model is established, which considers the thermal-mechanical coupling and ice-water phase change. Based on the numerical simulation, the variation of the temperature field as well as the expansion process of the frozen soil curtain are analyzed, and the effectiveness of the numerical model is further validated by comparison between the measured and simulated results. Thirdly, variations of three key parameters including the output energy, elastic strain energy and heat energy during the active freezing period are calculated and analyzed. Finally, the EUR curve during the AGF process is acquired based on the calculated indicators. The trend of EUR can be divided into four stages, while the EUR is zero in the initial stage, reaches a peak of 0.79 in the rise stage, and then decreases slowly in the decline stage and stable stage. According to the EUR curve, constructive measures to improve energy conversion and utilization are proposed. It is concluded that this novel method is very effective for the assessment of energy utilization in AGF projects.