Abstract
Subsea shield tunnels usually serve in a typical corrosive marine environment. Under the action of chloride penetration and carbonization, tunnel lining segments are often damaged because of concrete strength loss and steel bar corrosion induced concrete cracking during their service life, which seriously degrades the service performance of the tunnels. A systematical experimental and numerical investigation into the performance degradation of subsea shield tunnel segments accounting for concrete strength loss and steel bar corrosion is presented in this paper. The study demonstrates that chloride penetration decreases the peak strength and elastic modulus of the segment concrete by 42% and 46.1%, respectively. The average of the ratio of dissipated energy to the total energy of dry concrete is much smaller than that of water saturated concrete and chlorine solution saturated concrete, and chloride penetration reduces the energy storage capacity of concrete, and the ability to resist damage is weakened. When steel bars corrode for 120 days, the outer cracks continue to extend, and the concrete around the inner steel bars just begin to crack initiation; when corrode for 20 years, the length of the inner cracks gradually exceeds that of the outer cracks, and the inner cracks initiating from different steel bars coalesce with each other and form a continuous failure surface, causing great serious damage to the segment. Due to the difference in concrete strength, for the outer layer, the evolution processes of steel bar corrosion-induced cracks show the characteristics of early initiation, slow propagation, and late coalescence, and those for the inner layer have the characteristics of late initiation, rapid propagation, and early coalescence. During the whole process the propagation speed of the inner and outer cracks appears to be fast first and then slow. Moreover, the study also illustrates that the final state of segment performance degradation after crack coalescence presents the characteristics of whole lamellar exfoliation of the concrete cover.
Highlights
Shield tunneling has become a widely used construction method for subsea tunnels due to its strong adaptability to geological conditions, quick and safe construction, and low water inrush and collapse on the tunnel face [1]
This study intends to make some explorations on the time-variant durability damage evolution process and performance degradation characteristics of the lining segment of subsea shield tunnel with considering concrete strength loss and steel bar corrosion-induced concrete cracking. is paper is based on the conventional triaxial compression tests; the strength, deformation, and energy evolution characteristics of segment concrete under seawater erosion were analyzed from the mechanical and energy perspectives. en, based on the strength and deformation parameters acquired from the above test, the performance degradation process and corresponding characteristics of the lining segment were studied by a series of numerical simulations; it has certain guiding significance for the study of the durability of submarine shield tunnels and provides a certain reference for future related research
+2.167e+08 +1.969e+08 +1.772e+08 +1.574e+08 +1.377e+08 +1.179e+08 +9.817e+07 +7.842e+07 +5.867e+07 +3.892e+07 +1.917e+07 -5.750e+05 -2.032e+07 (b) that of the outer cracks, and the inner cracks initiating from different steel bars coalesce with each other and form a continuous failure surface, causing great serious damage to the segment
Summary
Shield tunneling has become a widely used construction method for subsea tunnels due to its strong adaptability to geological conditions, quick and safe construction, and low water inrush and collapse on the tunnel face [1]. E existing research achievements have played a significant role in promoting the study on durability performance degradation of subsea shield tunnels They only focus on a single degradation behavior between concrete strength loss and steel bar corrosion-induced concrete cracking, and few explorations consider the combined action of both. Erefore, the durability damage of the outer layer is caused by the combined action of concrete strength loss and steel bar corrosion-induced concrete cracking For this reason, this study intends to make some explorations on the time-variant durability damage evolution process and performance degradation characteristics of the lining segment of subsea shield tunnel with considering concrete strength loss and steel bar corrosion-induced concrete cracking. Erefore, the weakening effect of seawater corrosion on the strength of segment concrete should be considered in the performance degradation analysis of subsea shield tunnels. Ud Ue εi Figure 5: Relationship curve between dissipated energy and releasable strain energy of rock [16]
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