Study On The Safety Of The Longitudinal Cracking Running Tunnel Based On The Fracture Mechanics

Wulong Zhongxing Tunnel of Yu-Xiang Expressway, a super-long tunnel of twin single-track, was completed and went into operation in 2009. However, in the regular inspection 2013, there was severe cracking found in the lining structure of tunnel. It is an ultra-wide crack in the tunnel lining to endanger the safety of tunnel structure. But there are a lack of any analyses about the causes of serious cracks found in Zhongxing tunnel. The paper, against an engineering background of the cracking of Zhongxing Tunnel, utilizes the theory of fracture mechanics to carry out a safety analysis of the tunnel and then takes different crack parameters as the variables to analyze their impact on the safety of tunnel. The main research content & significance is as follows:①The methods of studying the safety of cracked lining structure of tunnel are acquired on basis of the theory of concrete fracture mechanics and the checking calculation methods for the section strength of uncracked structure, to estimate the section strength is sufficient to ensure the safety of cracked structure.②A simplified finite element model is established for the cracked lining structure: The solid element PLANE183 is adopted to simulate the 2nd lining, the surface element BEAM3 to simulate the primary lining, and the spring element COMBIN14 to simulate the ground spring. The crack route is set by means of the method of displacement extrapolation in the post-processing of ANSYS to compute the crack-tip stress intensity factors K, K of the 2nd lining; the stability of crack tips is analyzed on basis of the engineering fracture criterion to obtain the lining crack-tip stability coefficient defined in this paper. The crack-tip stability coefficients on different working conditions are calculated so as to determine the safety of the cracked lining structure of Zhongxing Tunnel.③The paper, as for the lining structure of tunnel, probes into the impact of crack depth, position and angle on the change law of crack-tip stress intensity factors, and gets the rule of the influence of crack depth, position and angle on the safety of tunnel structure.