The Safety Evaluation On Supporting Structure Of City Tunnel In Service

At present, China has become one of countries in the world that has the largest, the most complicated, the fastest-growing tunnels. As the development of chinese municipal construction, the city tunnels are constantly increasing. Because of the influence of geological conditions, terrain conditions, climatic conditions, the investigation, designing, construction, surrounding buildings and running, etc. So that different extent diseases, such as lining split, leakage water, cavity behind lining, lining corrosion will appeared in city tunnel in service, and these diseases and endanger may have tremendous influence and threats to the safety and normal running of city tunnels in service. Therefore, it is the particularly significant task to study the city tunnels in service's safety evaluation that tunnels are in all kinds of complex circumstances and conditions. Especially the system research in our country is still at the preliminary stage, lack of experience, so an in-depth research shows its urgency even more. This paper is based on certain city tunnel in service which has diseases in Chongqing, give its supporting structure the comprehensive safety evaluation, and through the results of the evaluation, judge whether adopt maintenance repair or disease punishment. The main work and results are as follows:â‘ From the types of diseases, analyse the causes of various diseases and its hazards. According to the analysis, the main diseases of the city tunnel in service's supporting structure are: lining thickness diminish, local lining intensity reducing, cavities behind lining, lining cracks and water leakage. Aim at various diseases, summarize and analyse the diseases detection method, consider that the most feasible means are geological radar etc, non-destructive testing method, the core-drilling method should be given cautiously.â‘¡Adopt finite element analysis, analyse the lining thickness diminish, cavities behind lining, partial lining intensity reducing, gained the development of lining cracks and the safety factor of the lining sections; analyse different locations and different sizes cavities behind lining that affect its under stress and stability; analyse the stress changes and the expansion of the plastic zone when cracks appeared in arch lining. Gained the following conclusions: the safety of lining has a greater impact when the effective thickness of arch and wall less than two-thirds; local lining intensity reducing, the safety factor of the corresponding location decreases, the major affected parts are feet of arch and upper of straight wall; there are definite impact on corresponding and adjacent location's safety factor when cavities appeared behind lining, it has little influence when cavity smaller (less than 0.5m); cracks of lining arch make the tensile stress of tunnel arch feet increased, and the maximum compressive stress occurs in the vault.â‘¢According to the disease characteristics of the project, monitored this disease tunnel one and a half years adopt that joint meter, strain gauge, anchored bar meter and multiple point extensometer, make out the system analysis about crack, strain and displacement development of the tunnel.â‘£Synthesize these three aspects study above, in conjunction with the relevant criterions, put forward proposed evaluation system based on the characteristics of the city tunnel in service. Finally, work out safety evaluation to support structure of certain city tunnel in service in Chongqing, educe that the tunnel should be early punished.