The Research Of Disaster Mechanism Of Highway Tunnel Lining Cracks

As one of the most common problems of highway tunnel,Lining cracking of highway tunnel has been existing for a long time and seriously influences project qualities and traffic safety.At present,most of the tunnels in operation are in the state of working with cracks,therefore,we have to consider the influence of cracks on lining when evaluating lining in operation,otherwise there will be great limitations in the assessment.However,the reasons for lining cracking are various and complex,such as random distribution of surrounding rock types and joints,holes in lining and insufficient lining thickness,disturbance caused by blasting,nonstandard construction and so on.So now it is difficult to study the interaction of tunnel lining,secondary lining and surrounding rock.Based on discrete element software PFC,this paper conducts numerical simulation analysis on tunnel lining under different working conditions.This paper simulates mechanism of crack propagation in cracked tunnel lining according to the stress distribution law of the cracked secondary lining of the highway tunnel obtained by the excavation loads due to unloading effect of tunnel excavation.At the same time,this paper makes comparative analysis on different stress states of surrounding rock and loading features of initial crack location and angle,and,combining theoretical learning,makes profound analysis and study on the causes,types,production mechanism and failure modes of various cracks in tunnel lining.The main work of this paper is as follows:(1)Collecting the existing highway tunnel lining cracks and tunnel crack rating standards,The paper conducts an investigation on the cracks of highway tunnels at home and abroad,then initially finds out the causes of cracks after classification and anlysis.Most of the existing rating standards are aimed at cracks in the lining of railway tunnels,and because of the difficult to achieve the depth of cracks in the lining,the evaluation system mostly considers the influence of width and length.Therefore,the influence of the crack depth on the lining of highway tunnel is simulated.(2)According to Code for Design of Highway Tunnel(JTG D70-2004),the effects of III,IV,V,VI grade rock of tunnel lining is simplified as a vertical load and uniform load.Based on the discrete element software PFC single axis compression module,the meso parameter of C30 concrete is calibrated,and the model of tunnel lining is built with the load obtained.(3)Through PFC2 D software,the paper demonstrates the propagation pattern of the preset crack under the the grade V surrounding rock,buried depth of 27 m and the second concrete lining thickness of 50 cm.The preset cracks are located on the arch,shoulder and vault respectively and the depth are set on 100 mm,200mm,300 mm,400mm respectively.The width of pre crack is 10 mm.The influence of the crack depth on the tunnel lining is summarized from four aspects: the number of the final crack,the maximum displacement and the maximum velocity of the lining,the number of sliding bond cracks and the crack opening.(4)In PFC3 D software,the effect of different crack lengths on tunnel lining is simulated by changing the preset crack length.The existing data are processed statistically,and the depth and length of tunnel lining are established based on Python language.