The corrosion expansion force and cracking separation between corroded section steel arch frame and shotcrete in tunnel primary support

Abstract

High chloride content in the subsea tunnel environment leads to inevitable corrosion of I-shaped steel in primary support. Corrosion generates expansive force between I-shaped steel and concrete, eventually cracking the concrete protective layer, and weakening the bond strength, severely impacting the tunnel support system’s durability. The main purpose of this article is to obtain the corrosion expansion force generated at the interface between corroded I-shaped steel and concrete, as well as the mechanical response characteristics of concrete under the action of corrosion expansion force. Firstly, nine I-shaped steel concrete components were fabricated for electro-accelerated corrosion test, obtaining the variation curve of corrosion expansion force with corrosion rate and protective layer thickness. The experimental results indicated that the development of corrosion expansion force can be divided into three stages: initial free corrosion stage (corrosion rate ρ = 0.5 % – 0.7 %), stage with a noticeable increase in corrosion expansion force (corrosion rate ρ = 0.7 % – 12 %), and expansion-induced cracking (corrosion rate ρ > 12 %). Meanwhile, a three-stage corrosion expansion force model for concrete and corroded I-shaped steel was proposed, which was correlated to the experimental curve well. Finally, the mechanical characteristics of the surrounding concrete during the development process of different corrosion expansion forces were explored through ANSYS software. The numerical results indicated that these cracks due to corrosion expansion force primarily occurring in the contact region between the concrete and the I-shaped steel flange, specifically in three areas: the central part of the flange and its two corners; The tensile stress in the concrete surrounding the web plate is less than that at the flange, leading to the initial longitudinal cracking observed on the outer surface of the flange.