Field measurement and mechanism of inclined and vertical piles in foundation pits

The inclined and vertical support for foundation pits is a kind of unsupported support system, which is formed by using the crown beam to connect the vertical cantilever pile and the inclined pile. The measured results of the existing projects show that the inclined and vertical alternate support has better anti-overturning and deformation control capability. However, there is still a lack of systematic research on the mechanism of inclined and vertical alternate support from the perspective of pile stress. Based on the field tests on the inclined and vertical alternate support piles in a foundation pit project in Tianjin, the forces of the inclined pile are monitored and analyzed. On this basis, the numerical modeling is carried out by using the finite element software PLAXIS. The mechanism of the axial forces of the inclined pile and the influences of the inclined angle and the arrangement of the inclined and vertical piles on the supporting performance are studied. The results show that the axial forces of the pile shaft are greater than those of the single-row inclined piles and double-row support piles, and the effect of inclined support is obvious to the deformation control of the support structures. The effect of inclined support is mainly due to the relative displacement of the inclined pile and the soil in the passive area to produce the side friction resistance of the pile. At the same time, it is found that increasing the inclined angle of the inclined pile is conducive to the inclined support of the inclined pile, which makes the lateral displacement of the support pile decrease, but the maximum positive bending moment of the pile shaft will increase at the same time. In addition, under the same amount of piles, different arrangements of inclined and vertical piles have small influences on the deformation of the support. The arrangement of one inclined and two vertical piles can reduce the stress of the vertical pile and the construction difficulty.