Influence of voids behind lining on the mechanical behavior of lining structure of highway tunnel in watery strata
FANG Yong1,GUO Jianning1,KANG Haibo2,XU Chen1
(1. Key Laboratory of Transportation Tunnel Engineering,Ministry of Education,Southwest Jiaotong University,Chengdu,Sichuan 610031,China;2. Branch of Road Tunnel,Sichuan Road and Bridge Construction Co.,Ltd.,Chengdu,Sichuan 610200,China)
Abstract:The existence of voids behind highway tunnels in water-rich strata deteriorates the stress state of the lining structure,make it vulnerable to cracking and affects its integrity during service. A device for external loading test was therefore developed with a controllable air pressure between the primary and secondary linings. The voids can be simulated by regulating the pressure difference,equivalent water pressure in the voids. Using this device together with a tunnel-ground simulation facility,a model test with a geometric similarity ratio of 1:30 was conducted. The force distribution and cracking features on the secondary lining with respect to different external water pressures and void distribution were analyzed. The axial force and bending moment distribution on the secondary lining were found no longer be symmetrical due to the voids. The voids at different location impacted differently to the mechanical behavior of lining,especially at locations near the voids. In the area close to the voids,the axial force and bending moment increased at a rate significantly higher than in other parts of lining. As the external water pressure increased,a nearly linear increasing trend of axial force and bending moment was observed irrespective of the void locations. The eccentricity decreased as the water pressure rose,and it tended to remain constant once the water pressure reached 150 kPa. Given the same pressure level,the axial force and the bending moment in tunnels with widening band were significantly greater than that in three-lane tunnels,though the distribution was similar. In the cases where the vertical stress field dominated,the voids behind the left wall had the most significant effect on the bearing capacity of lining,followed by voids behind the crown and invert. Both the number and severity of cracks on the lining with voids presented nearby exceeded the other parts noticeably.
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