为研究矩形顶管隧道在地基沉降及上部荷载变化等情况下F型承插接头的抗弯性能、变形规律及破坏特征，在管节底部布置不同数量的等效地基弹簧来模拟不同地质条件，开展不同地层条件下的接头弯曲试验。试验结果表明： 1）加载初期，接头弯曲变形主要为钢套环变形，各等效地基下接头抗弯刚度差异较小。2）当位移加载至15~25 mm时，管节顶底板内侧与侧墙外侧出现裂缝，由于管节自身变形使得接头张开量随着加载位移的增大出现减缓，接头抗弯刚度曲线斜率增大，并以0.007 rad张开量为界线划分为2个阶段。3）根据拉线式位移计变化、接头混凝土应变及钢套环应变可知，顶底板中部及侧墙中部挠曲应力最大，且在上方荷载作用下，管节表现出被压扁的趋势。4）接头弯曲变形中，插口端混凝土会与承口端混凝土及钢套环发生挤压，顶板混凝土被压碎，钢套环由于挤压而发生翘曲。
The bending mechanical performance, deformation
mechanism, and failure characteristics of an Ftype
socket joint in a rectangular pipejacking 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.
