## 1 Introduction  
As the country's economy had developed, the construction of tunnels in China has entered an era of rapid development [1, 2]. More and more super-span tunnels have been proposed in the fields of water conservancy, transportation and municipal engineering [3, 4, 5]. Table 1 has shown a few typical super-span tunnel examples that have been constructed in China in recent years. Over the past 30 years, Japan, South Korea and some European countries have also accumulated significant experience in constructing super-span tunnels [6]. Super-span tunnels differ from conventional cross-section tunnels in that they have characteristics of super spans, complex support structures and frequent stress conversion between the surrounding rock and the support structures during the different excavation stages. Therefore, designing the support structures, selecting the excavation methods and studying the stability of the surrounding rock of super-span tunnels are widely considered by scholars. A series of researches have been carried out in the field of super-span tunnels [7; 8; 9]. Some achievements have been made in the design of supporting structures. [PERSON] et al. [10] evaluated the installation timing of the initial ground supports for a super-span tunnel constructed in hard rock. [PERSON] et al. [11] proposed a new supporting method of shallow buried super-span tunnel based on small tunnel sheds. [PERSON] et al. [12] demonstrated that using a steel-tube-slab structure combined with the pile-beam-arch method is an effective approach when constructing a super-span underground station. Some scholars also focused on the selection of the excavation methods. [PERSON] and [PERSON] [13] introduced a successful application of a method for construction of the Mansour Station based on a new pre-supporting system. [PERSON] and [PERSON] [14] studied the effectiveness of the multi-micro shield tunneling method in super rectangular cross-section tunneling. [PERSON] et al. [15] analyzed the effect of the central diaphragm and side wall drift methods on the disturbance control of the surrounding rock during excavation of a super-span tunnel. [PERSON] [16] analyzed the construction concepts of the sequential excavation method as well as new Austrian tunneling method through a case study of a series of super-span tunnels. In addition, some breakthroughs have been made in the study of the stability of the surrounding rock stability. [PERSON] et al. [17] simulated the deformation and failure evolution of the surrounding rock of the Laohushan tunnel using the improved discontinuous deformation analysis method as well as binocular stereo photography measurement technology. [PERSON] et al. [18] carried out field investigations for five different tunnels located in the Himalayas in India in order to study blast induced rock damage around tunnels. [PERSON] [19] calculated the response curve and analyzed the radius of the excavation damage zone by combining damage constitutive models with the convergence-confinement method. It can be seen that the above studies were mostly based  
on experimental investigations, numerical simulations and theoretical analysis. The experimental investigations are mainly influenced by scale effects, and the numerical simulations are excessively dependent on the construction of the model and the parameters that are selected. In addition, it is difficult to use the results of the theoretical analysis as the basis for the design and construction of super-span tunnels due to their inability to deal with complex situations. As the most intuitive and effective research method, field monitoring has rarely been used in study of super-span tunnels; this is because the complex construction process poses considerable difficulty in the installation and preservation of the monitoring elements. The super-span transition section of the Badaling Great Wall station has great research value because its maximum span reaches 32.7 m; this is 1.5 times the span of most super-span tunnels.