Analysis Of The Common Defects On In-Service Urban Tunnels And Repairing Effects

At present China has become one of the countries with the largest, most complex and fastest growing tunnel projects. With the continuous development of urban construction, urban tunnels are constantly increasing. However, according to a lot of information obtained from related researches, it has been noted that due to the impact of geological conditions, terrain conditions, weather conditions and survey, design, construction, operations and other aspects of the surrounding buildings, the defects of lining such as cracking, leakage of water, back cavity and corrosion occur on the urban tunnel in-service. These defects and hazards have a huge impact and threat to tunnel in-service.The safety evaluation of urban tunnels in-service on a complex environment is the main focus of our study. In particular, the system being studied in this research is still in the preliminary stage, hence the need for urgency to carry out in depth study on this area. This thesis is thus based on the defects of a BAYI and XIANGYANG tunnels in Chongqing, China, with the objective of comprehensively evaluating the safety of the supporting structure. In this research, the work and results are as follows:?From the type of defects, the analyses of the causes and effects of the defects have been made. According to the analysis, the main defects of tunnel support structures are: lining thickness diminished, caves existing behind the lining, lining cracks and water seepage. Based on the characteristics of the various defects, we summarized and analyzed the detection method of the defects.?Using the finite element numerical simulation, analysis of the impact of the lining thickness reduction, cavity behind lining, the strength reduction of the safety factor was done. Then analyze of the impact of the cavities'location and size, and cracks to the stability of the tunnel. Furthermore, analyzes of the stress changes of the existing cracks and the development situation of the plastic zone. Thus, we draw the following conclusions that: When the effective thickness of the arch and the side wall lining is less than 2/3, lining has a greater impact on safety; When the strength of local lining reduces, the safety factor is reduced, especially the arch and the top of the side wall. When cavities appear at the back of the lining, the safety factor is been impacted, but when the cavity is small(less than 0.5m), the influence is little. When cracks appear at the arch of lining, tensile stress at the tunnel arch increases and the maximum compressive stress are observed in the crown.?Using the finite element numerical simulation, analyzes of the impact of the different sizes of vault cavity, arch side cavity, arch foot cavity and different thicknesses of the tunnel lining after repair was done .We draw up conclusions as follows: If the cavity is bigger, the stress in the rock mass around the cavity is larger; and if the cavity is grouted, the stress delivered to the vault is also bigger, and the weight of the fill is increased. As the interface between the fill and rock mass gets larger, the transmission force from the rock mass to the grouting material, then to the lining increase. The influence of the axial force of the lining is not obvious, as the sizes of the cavities changes. The moment and shearing have the same sign in arch side or arch foot, whereas moment and shearing in vault has opposite signs. If the cavity is bigger, the stress concentration is more serious and the area where the stress diffuses is larger. When the lining is thin, it will endure more stress and the stress in the lining grows up, conversely, when the lining is thick, the stress can be dispersed in the lining and is more homogeneous. If the lining is thicker, the weight of lining is greater and the stress of the lining grows higher. The horizontal or the vertical displacement increment is changed nonlinearly with the thickness of the lining.?According to the defects characteristics of this engineering example, the defected tunnel has been monitored with seam meter, strain gauge, anchor gauge and multipoint displacement instruments for a year and a half. The development of tunnel crack, displacement and strain has been analyzed systematically.