Construction Technology of Super-large Section of Highway Tunnels with Four or More Lanes in China

With the rapid development of the economy, higher vehicle requirements are being put forward for highway transportation. Newly built and expanded super-large sections of single-span highway tunnels with four or more lanes frequently appear; however, few scholars have systematic studied these. Many studies often overlook the more detailed categories of engineering cases, and are unreasonable in both analogy and citation. Based on an extensive and in-depth investigations, this study classifies super-large sections of highway tunnels with four or more lane into three categories according to their causes and characteristics: conventional newly built four-lane highway tunnels, in-situ extensions of four-lane highway tunnels, and bifurcated highway tunnels with four or more lanes. On this basis, the study both summarizes and analyses the technical status of the section shape, construction method, construction mechanics, and support parameters of highway section tunnels; shortcomings in this and other research are also investigated. In the study of section shape, it was determined that the flatness rate used in practical projects fluctuates widely, and is larger than the flatness rate obtained by the current theoretical research used in most foreign tunnels. As such, a more reasonable flatness rate needs to be studied in depth. In the study of construction methods, it was found that there is a tendency to gradually reduce excavation sections, expand construction space, and enhance mechanized construction. Construction machinery with higher degrees of automation is therefore in urgent need of research and development. In the study of construction mechanics, despite the fact that the load release and progressive failure process of surrounding rock are more deeply understood, it was determined that there is still no uniform and convincing calculation theory for the pressure calculation of the surrounding rock in deep buried sections. On the research of support parameters, it was noted that there are great differences among different projects; it is necessary to further study and optimize the support parameters of super-large flat tunnels so as to lay a theoretical foundation for perfecting the corresponding guidelines or codes. Finally, the construction technology of four or more lane super-large cross-section highway tunnel was prospected. It was pointed out that the standardization of design, mechanization of construction, and lightening of structures are the key targets for research in the future. © 2020, Editorial Department of China Journal of Highway and Transport. All right reserved.