<p>The liquid nitrogen artificial ground freezing (AGF) method is frequently employed in municipal emergency projects, such as reinforcement during shield cutterhead replacement and water sealing in deep foundation pits, due to its rapid freezing capability. Traditional AGF simulations often simplify the freezing pipe as a fixed temperature or heat flux boundary. However, liquid nitrogen undergoes intense boiling-phase-change heat transfer within the freezing pipe, resulting in a significantly nonlinear distribution of heat transfer intensity along the pipe. Neglecting this characteristic can lead to severe deviations in evaluating the development of the frozen curtain, thereby affecting engineering safety. Therefore, this study aims to establish a more realistic temperature boundary condition for freezing pipes that accounts for boiling heat transfer. First, systematic field experiments are conducted based on an actual liquid nitrogen AGF project. The influence of liquid nitrogen freezing on the evolution of the surrounding ground temperature is revealed. Second, a three-dimensional numerical model is established that only considers the convective heat transfer of nitrogen. Traditional boundary models severely underestimate the local freezing capacity in the boiling section. Finally, based on experimental observations, a temperature boundary considering boiling heat transfer is developed. The results demonstrate that the developed model can accurately reproduce the core characteristics of the measured temperature, including the non-uniform freezing pattern along the pipe and the time-history temperature curve trends at various monitoring points. The developed boundary model can more accurately simulate this asymmetric freezing effect characterized by "weaker upper and stronger lower" performance. It provides critical theoretical support and practical tools for optimizing the design of liquid nitrogen AGF projects—such as determining freezing pipe spacing and predicting freezing time.</p>