Model tests on initial freezing process of column foundation on slope in permafrost regions

The Qinghai-Tibet ±400 kV electrical transmission line traverses more than 550 km in permafrost regions, which may lead to a lot of frozen soil engineering problems for the foundations of transmission tower. Since the column foundation can not only reduce frost heave force but also provide higher bearing capacity, it has been accepted as the first choice of foundation design in permafrost regions. Considering the engineering background of the electrical transmission line, the stability of the column foundation in the initial freezing process is highlighted. In the laboratory, the model tests with a scale of 1:10 are carried out, and both the frost heave and the heave force of the column foundation are monitored. Based on the test results as well as engineering experience, suggestions for the design, construction and maintenance of the project are addressed. The model tests show that the heave force increases with the decreasing temperature in the foundation soil, and the horizontal heave force on the top of the foundation can rise to 130 kPa, while the normal heave force at the bottom can rise to 80 kPa. During the freezing process, the frost heave of the foundation is much greater. The vertical displacement of the foundation can reach 5.5 mm, and the horizontal displacement at the top of the foundation can reach 3.8 mm.