No External Load Causes Tunnel Sceondary Lining Crack Analysis And Research

Along with the rise of economic development and construction technology, tunnelengineering becomes more popular in railway construction, highway construction, urbantraffic engineering as it shortens the distance, saves both time and land. Due to the influenceof various factors, the secondary lining of some tunnels appear crack in many earlyconstructed tunnels and even some under construction ones. The emergence of crackseriously affects the stability and durability of tunnel structure. Moreover, it induces othertunnel diseases and throws a great threat to people’s life and property safety. Therefore, it isimportant to solve this problem in the construction and maintenance of the tunnel. This paperanalyzes the formation and development process for crack of secondary lining under noexternal and provides suggestions for its prevention and governance.Based on the scholars research about crack of lining concrete, we learn how the crackdevelop from micro to macro, and even damage the structure. From the perspective of tunnelconstruction methods, we try to learn different construction methods of the secondary liningand analyze the causes of cracks from the source. Different construction method will inducecrack of secondary lining with different reasons. For the early construction methods, thesecondary lining with the initial support to bear the loosening pressure and deformationpressure of the surrounding rock. Currently, secondary lining is almost not to bear the loosingpressure of surrounding rock, but protection. So the crack of secondary lining of tunnel is theinfluence of construction technique, load and environmental factors.Cracks of secondary lining for new tunnel are mainly the tensile crack. For those earlysecondary lining, due to the incomplete construction technology, early removal of shutteringand not timely maintenance and its gravity, vault becomes bending, making the lining archtransverse tensile and longitudinal cracks at the position of the secondary lining arch.By means of the analysis of the secondary lining tensile stress, tensile stress mainlycauses by temperature stress and dry shrinkage stress of the concrete and its own gravity. Bythe theory that the maximum tensile stress is through the gravity of secondary lining of tunnel,temperature stress and dry shrinkage stress, we calculate and analyze the results to find thecauses of cracks of second lining under no external load. Then the paper uses Ansys finiteelement simulation analysis. Based on the finite element numerical simulation, the results basically correspond with the result of the theoretical calculation. In order to get furtherunderstanding, this paper carried out analysis in case of the influence of gravity underdifferent working conditions under different working conditions and the change of thetemperature stress. We finally get the conclusion. First, arch displacement and tensile stress iscorrelated with arch tunnel arch span. The larger the span is, the greater its value is. Second,arch displacement and arch tensile stress is associated with the thickness of the lining. Thegreater the thickness is, the smaller the value is. Third, arch displacement and tensile stresshave nothing to do with reinforcement. Because of gravity, reinforced yet play a role. Whenthe concrete strength less than C35, thickness of single, double tunnel’s secondary lining is30cm should be equipped with tensile steel mesh, otherwise secondary lining easy to crackingdamage. Concrete structure is vulnerable to the temperature stress if the maintenance is notright in the early stage or meeting the bad environment. This leads to the cracks in concretesurface. Temperature stress is of a linear to calculating temperature change and thickness.Constant calculating temperature with increasing environment temperature leads to theascension of temperature stress. Thus, concrete pouring process should avoid maximumtemperature phase of the day. To achieve stable structure，Lining thickness shouldn’t be toolarge; calculation of concrete lining temperature does not exceed25℃, calculation of thetemperature difference contains dry shrinkage temperature11.4℃,so after pouring, secondlining’s changes in temperature should not exceed15℃; when calculated temperatureremains unchanged, increasing ambient temperature can elevate the temperature stress withincreasing thickness, therefore, when pouring, ambient temperature should not exceed35℃.From the analysis of no external load crack of second lining, combined with crack statusZhaojing Mountain along the ShenXia railway (appearance in operation), the paper analyzesthe influencial factors of the secondary lining crack, gets crack characteristics and mechanismof cracks and finally put forward the corresponding treatment measures.and that help tosupport technical for constructing tunnel, and also help to provide theoretical guidance fordesigning the subsequent tunnel secondary lining.