Freeze-thaw Cracking Damage Model and Verification of Expressway Semi-rigid Base in Region with Large Temperature Differences
Expressways in inland regions of China are generally affected by freezing and thawing with large temperature differences,resulting in semi-rigid base cracking and seriously affecting the service life and working performance.Clarifying the evolution process of thermally-induced cracking and constructing the freeze-thaw cracking damage model are the key scientific issues to be solved urgently for the long-term stability of semi-rigid base.First,taking the semi-rigid base of Wumu section of Beijing-Urumqi expressway as the study object,the freeze-thaw cycle tests with different freeze-thaw cycles were carried out.The evolution process of freeze-thaw damage in semi-rigid base was finely reproduced by means of ultrasonic nondestructive testing,nuclear magnetic resonance and scanning electron microscopy.Then,since the traditional thermally-induced cracking model of semi-rigid base did not consider the influence of freeze-thaw and the micro-element ability to bear residual thermally-induced stress after damage,the freeze-thaw damage model suitable for expressway semi-rigid base in regions with large temperature differences was established by introducing the freeze-thaw progressive damage coefficient.The model was based on the study and optimization on the traditional semi-rigid base cracking model,and verified by using the field monitoring results of semi-rigid base of Wumu section of Beijing-Urumqi expressway.The result indicates that the dynamic modulus of semi-rigid base in the first 6 freeze-thaw cycles decrease significantly by 47.93%,and then tend to be flat.As a whole,the base internal pores are characterized by the increased pores and increased pore size.The large pores proportion increases from 0 to 29.8%.The model was verified with the semi-rigid base strain and temperature monitoring data with the error range of 0.4%-6.0%.The model reliability and accuracy were verified.The study result can provide the basic theoretical reference for the cognition and evaluation on expressway semi-rigid base cracking process in regions with large temperature differences.
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