Abstract: Heated pipeline transportation is one of the most economical and effective methods for long-distance transportation of oil and gas resources. Among them, the interaction mechanism between high-temperature pipelines and soft soil foundations is the key to analyzing their service stability. During the long-term service of the heated pipeline, heat is transferred to the surrounding soft soil, triggering complex hydro-thermal-mechanical coupling behavior. This, in turn, alters the bearing capacity of the foundation, significantly affecting the stability of the pipeline in service. A model test system has been developed to simulate the interaction between high-temperature pipelines and soft soil foundations, capable of replicating temperature variations in the pipeline. Focusing on the cyclic temperature loading experienced during the start-up, shutdown, and operation of high-temperature pipelines, model tests were conducted under various conditions, including different pre-compression stresses in the foundation, pipeline heating powers, and heating methods. These tests aimed to explore the evolution of temperature and pore pressure in the soil surrounding the pipeline during its service life under cyclic temperatures. Furthermore, the study investigated the development of restraint forces in the surrounding soil and the changing bearing characteristics of the foundation. The test results indicate that during continuous heating, the pore pressure around the pipeline increases, peaking before significantly decreasing, and may even reach negative values. This phase is beneficial for pipeline stability. When subjected to cyclic temperature loading, fluctuations in temperature induce corresponding variations in the pore pressure of the foundation. It’s worth noting that the amplitude of pore pressure fluctuations is smaller at the sides of the pipeline compared to the top and bottom. In tests simulating pipeline uplift, the foundation reaches its ultimate bearing capacity when the displacement reaches approximately 1.2 times the diameter of the pipe. Additionally, a higher pre-consolidation pressure offers greater bearing capacity, although there is little difference in uplift capacity between super-consolidated and normally consolidated foundation soils. T-bar tests conducted on the foundation revealed a significant enhancement in foundation strength during the high-temperature phase maintained by a single heating cycle. Moreover, an increase in foundation strength was observed even after the heating was stopped.

Key words: heated pipeline, temperature loading, soft soil, bearing capacity, modeling test