## 5 Results
### Different Excavation Sequence  
To better guide the site construction, this study focuses on the comparative analysis of the influence of excavation sequence on the stability of surrounding rock during the construction of a shallow unsymmetrical loading section of a super-span tunnel. The study presents various excavation sequences for the double-side drift method, including the deep-side-first excavation sequence and the shallow-side-first excavation sequence. In Scheme 1, the specific construction sequence is as follows: (1) Excavation of deep side upper bench \(\rightarrow\) (2) Excavation of deep side lower bench\(\rightarrow\) (3) Excavation of shallow side upper bench \(\rightarrow\) (4) Excavation of shallow side lower bench \(\rightarrow\) (5) Excavation of middle drift. In Scheme 2, the specific construction sequence is as follows: (1) Excavation of shallow side upper bench \(\rightarrow\) (2) Excavation of shallow side lower bench \(\rightarrow\) (3) Excavation of deep side upper bench \(\rightarrow\) (4) Excavation of deep side lower bench \(\rightarrow\) (5) Excavation of middle drift. The simulation results of arch settlement, horizontal displacement, vertical stress, and plastic zone at two schemes are shown in Figures 10-12. From the arch settlement duration curve in Figure 10a, points 0 and 1 show continuous settlement changes, and point 2 shows a slow uplift trend; comparing the simulation results of Scheme 1 and Scheme 2: in Scheme 1, points 0 and 1 settled by 89.0 mm and 101.7 mm, respectively, while point 2 was uplifted by 21.4 mm; in Scheme 2, points 0 and 1 settled by 83.2 mm and 89.0 mm, respectively, while point 2 was uplifted by 17.9 mm. By comparing the results, it can be found that when the scheme of the deep side is adopted, the arch settlement of the deep side and the drift in the middle is greater than the scheme of shallow-side-first excavation, and the uplift deformation of the arch of the drift on the shallow buried side also shows the result that the first excavation on the field is greater than the first excavation on the shallow side. By analyzing the simulation results of the horizontal displacement of the tunnel from Figure 10b, it is evident that both points 5 and 6 exhibit a convergence pattern to the simulation results of Scheme 1 and Scheme 2. Specifically, the horizontal displacement of point 5 is 27.0 mm, while that of point 6 is \(-\)0.3 mm. In Scheme 2, the horizontal displacement of point 5 is 26.1 mm, and that of point 6 is 0 mm. The horizontal displacements generated by the scheme of the deep-side-first excavation and the shallow-side-first excavation are basically the same, with no significant gap. Figure 11 illustrates the vertical stress contours of the initial support structure. The contours reveal compressive stresses are evident at the sidewalls of the initial support, while tensile stresses are evident at the tunnel arch and the inverted arch. The highest principal stresses are located at the foot of the arch on the deeply buried side, characterized by compressive stresses. Specifically, Scheme 1 exhibits a maximum compressive stress of 9.54 MPa, whereas Scheme 2 shows 10.12 MPa. Conversely, the top of the arch experiences the maximum tensile stresses, with Scheme 1 recording 0.44 MPa and Scheme 2 at 0.36 MPa. Notably, the maximum tensile stress occurs at the top of the arch, where Scheme 1 reaches 0.44 MPa and Scheme 2 measures 0.36 MPa. Importantly, both the maximum compressive and tensile stresses of the initial support are below the standard strength value of C25 shotcrete. This observation suggests that excavating the shallow buried side first is advantageous as it allows the initial support to supply compressive stress effectively, thereby controlling the deformation of the support structure. Figure 12 shows the distribution of the plastic zone at the end of tunnel excavation for both schemes. The figure indicates an asymmetric distribution of the plastic zone of surrounding rock due to the influence of topographic bias.