## 1 Introduction  
Because of its advantages of a smooth alignment, a small footprint, and excellent space utilization, the double-arch tunnel becomes one of most widely used types of tunnel structures, and it is frequently employed in highway engineering. Thus, the mechanical behavior of the tunnel is regarded by many scholars in terms of the deformation laws of the tunnel lining and surrounding rock, as well as the control measures to restrain the deformation of the tunnel and surrounding rock [1, 2, 3, 4]. Generally, the engineering behaviors of different geotechnical structures can be well reflected by numerical simulation [5, 6, 7] and experimental investigation [8, 9, 10]. [PERSON] et al. [11] investigated the deformation characteristics of the crossing section of two municipal tunnels subjected to construction load by on-site experiments. [PERSON] et al. [12] investigated the behavior of a tunnel caused by adjacent excavation and established a reference for excavation standard. [PERSON] et al. [13] discussed the influence of the stiffness of tunnel lining on the displacement and distortion by on-site investigation. [PERSON] et al. [14] predicted the deformation of the surrounding rock around the tunnel based on different calculation models or methods. The construction method for the double-arch tunnel includes the double-side-drift method, the CD method, the bending method, and the CRD method [15, 16]. The different methods are suited for different engineering geological conditions, and the suitability of different methods for the construction tunnels has been discussed by many scholars [17, 18, 19, 20, 21]. [PERSON] et al. [22] studied the construction techniques of the entrance of an urban double-arch tunnel to improve the construction efficiency and ensure the stability of the tunnel entrance section. [PERSON] [23] optimized the distribution of the stress release ratio to determine the proper installation time for the secondary liner. Considering the skewed distribution characteristics, [PERSON] et al. [24] built a computational model of a double-arch tunnel to analyze the pressure evolution of the surrounding rock during step-by-step excavation of a double-arch tunnel. [PERSON] et al. [25] presented analytical solutions for internal forces of a lining structure in a shallow double-arched tunnel subjected to unsymmetrical loading. The deformation mode of the arch structures of the tunnel can be determined based on the curved beam theory, and a more accurate inversion analysis scheme can be proposed [26]. However, in engineering practice, the tunnel is generally constructed under a sloping mountain, which subsequently results in different burial depths for different caverns. An open-buried double-arch bias tunnel structure system is no longer compatible with the concealed excavation method for excavation [27]. [PERSON] [28] described the design and calculation of a large-span open-buried double-arch tunnel from the aspect of engineering design. [PERSON] et al. [29] adopted finite element software to analyze the stress distribution and displacement characteristics of surrounding rock and linings in two types of open-buried tunnel structures, half-road and half-tunnel, subjected to different construction conditions. The existing literature has greatly developed the construction technology of tunnels. However, due to the constraints of the terrain and the complexity of the construction process, the varied open-buried double-arch tunnels with different section forms show different engineering mechanical behaviors. In this study, based on an open-buried double-arch tunnel on Xiajuan Road, Changsha city, China, the evolution of the deformation of the surrounding rock and the mechanical properties of the supporting structure of the open-buried double-arch tunnel subjected to construction load are studied. The study aims to provide a basis for the optimization of the supporting structure and a guideline for the construction plan of the tunnel, as well as a reference for the design and construction of related tunnels.