# Deformation Analysis of the Rock Surrounding a Tunnel Excavated through a Gently Dipping Bed
## 1 Introduction  
In the construction of transportation networks in southwestern China, there are increased cases of tunnel construction through foliated rock, such as the Daliangmg tunnel of the Wuqi Expressway [1], the Muzhailing tunnel of the Lan-Yu Railway [2], and the Yangjiang tunnel [3]. Unlike isotropic surrounding rock masses, the deformation and strength of foliated surrounding rock masses display obvious anisotropy. Due to problems related to the deformation and stability of foliated surrounding rock masses encountered in engineering, the concept of anisotropy has gradually entered the vision of scholars and has been studied in depth [4; 5; 6]. The anisotropic properties of foliated surrounding rock masses, i.e., strength and deformation, have a great impact on the deformation and damage characteristics of the surrounding rock masses. Usually, when tunneling under foliated surrounding rock masses, the deformation of the surrounding rock masses exhibits obvious asymmetry. In addition, when the dip angle of the bedding plane is less than 30\({}^{\circ}\), both the top and bottom of the tunnel are prone to damage. In the past, the tunnel span of the railroad industry was relatively small, and the engineering properties of the gently inclined rock layer did not attract sufficient attention. However, with the increase in tunnelconstruction under the complex geological conditions of southwestern China, the technical problems encountered in construction involving a gently inclined rock layer have gradually received more attention [7; 8; 9]. In addition, with the increase in the number of long tunnels, to achieve tunnel penetration as soon as possible, it is often necessary to use inclined shafts or horizontal adits to increase the auxiliary working face for tunnel construction, which shortens the construction period. Compared with inclined shafts, horizontal adits have lower environmental requirements and are widely used in certain geological environments, such as those with large burial depths and high ground stresses; thus, it is becoming more common to use horizontal adits to increase the auxiliary working faces during tunnel penetration [10]. However, the simultaneous construction of two excavation working faces leads to superposition of the disturbance area, which has a serious impact on the stability of the tunnel and is more dangerous than one-way tunneling. For foliated surrounding rock, due to the weak plane of the gently inclined rock, it is more difficult to control the stability of the surrounding rock. If the excavation method is not appropriate or the support design is not reasonable, it can easily cause tunnel collapse, delay in the construction schedule, increased project input, and safety problems. Therefore, the selection of the tunnel penetration working face is a key point in the construction of a tunnel through gently inclined, foliated surrounding rock.  
In this study, the deformation caused by the excavation of the two-stage cross-section of the Yuelongmen Tunnel of the Chengdu-Lanzhou Railway in southwestern China was compared with the deformation results of the FLAC3D numerical simulation. Based on this, the deformation caused by tunnel excavation through gently inclined rock was analyzed to provide a reference for the selection of reasonable construction methods.