Abstract: The bending mechanical performance, deformation mechanism, and failure characteristics of an Ftype socket joint in a rectangular pipejacking tunnel are investigated under conditions of foundation settlement and variations in the upper load. Different numbers of equivalent foundation springs are arranged at the bottom of the pipe to simulate different geological conditions, and joint bending tests are conducted. The following results are obtained from the tests: (1) The bending deformation of the joint is mainly caused by deformation of the steel collar at the initial stage of loading. There is a small variation in the bending rigidity of the joint under different equivalent foundations. (2) When the loading displacement reaches 15~25 mm, cracks appear on the inside of the top and bottom plates as well as the on the outside of the sidewall. As the loading displacement increases, the change rate of the joint opening decreases and the slope of the bending rigidity curve for the joint increases because of the deformation of the pipe joint itself. There are two regimes in the bending rigidity, where the transition between these regimes occurs at a joint opening of 0.007 rad. (3) Based on the change in the reading on the wire displacement gauge, the highest strain occurs in the joint concrete and the steel collar and the highest flexural stress occurs in the middle of the roof and floor and the middle of the sidewall. The action of the upper load induces flattening deformation of the pipe section. (4) During the bending deformation of the joint, the socket concrete is squeezed along with the jack concrete and the steel collar, the roof of the socket concrete is crushed, and the steel collar warps because of concrete extrusion.

Key words: rectangular pipejacking, Ftype socket joint, model test, bending stiffness, mechanical property, deformation mechanism