## 5 Conclusions  
In this study, the construction process was numerically simulated by establishing a multistratum-tunnel 3D elastoplastic finite element model, and an in-depth investigation of the ground settlement pattern and deformation influencing factors during the construction of a two-lane tunnel was conducted to analyze the mutual influence mechanism between the two tunnels during construction. The main conclusions are as follows:  
1. When the distance between tunnel excavation faces gradually increases, the degree of mutual influence of the two-lane tunnel is smaller, resulting in smaller ground settlement values and greater influence on the surrounding soil. Because the excavation load is mainly borne by the surrounding rock of the right tunnel during the excavation stage of the right tunnel first, and the load is shared by the left and right tunnels after the excavation of the left tunnel, the settlement value in the direction of the right tunnel is slightly larger. When the spacing between tunnel excavations is greater than 75 m, there is little interaction between the tunnels. Therefore, it is  
Figure 15: Variation curve of displacement at different monitoring points with the water level on the riverbed side. recommended that the spacing be greater than this distance so that the settlement can be kept within acceptable limits. 2. For the tunnel depth, when the tunnel depth increases, the ground settlement curve changes from a W-shaped curve to a V-shaped curve, the maximum value of ground settlement moves from the surface above the right hole vault to the vertical centerline and the number of ground settlement increases. However, the ground settlement will show a trend of a large increase first and then a gentle increase, which is caused by the soil arch effect. 3. As the tunnel spacing increases, the ground lateral settlement curve changes from V-shaped to W-shaped. The final ground settlement curve is obtained after the superposition of two single-line tunnel excavations, so when the tunnel spacing becomes larger, the degree of mutual interference during excavation becomes weaker, resulting in a smaller superposition area of ground settlement caused by the twin-tunnel excavation. 4. The higher the water level on the riverbed side, the greater the settlement value of the ground, with the maximum settlement occurring at the centerline of both tunnels. The ground settlement is less affected by changes in water level, due to the fact that the weight of the river water is less than the unit weight of the soil. Nevertheless, when a tunnel through a river is excavated, the period when the river level is low should be chosen. 5. By comparing the values of maximum surface settlement between different factors, it can be found that the distance between tunnel excavation faces has the greatest influence on surface settlement, followed by the tunnel spacing and the tunnel depth and finally the water level on the riverbed side. This can give some useful suggestions for better control of surface settlement during the actual construction of the project. In the actual construction, more attention needs to be paid to the distance between tunnel excavation faces. Conceptualization, H.D., P.C., Y.L. and Z.L. ; Formal analysis, H.D. ; Investigation, G.M., Z.F. and W.X. ; Methodology, H.D. and P.C. ; Resources, G.M., Z.F. and W.X. ; Software, H.D. and Y.L. ; Writing--original draft, H.D. ; Writing--review & editing, Z.L. All authors have read and agreed to the published version of the manuscript. This research was funded by the National Natural Science Foundation of China (Grant No. 11772358, 52004327); the Water Conservancy Science and Technology Major Project of Hunan Province, China (Grant No. XSKJ2019081-10); and the Fundamental Research Funds for the Central South University, China (2020 zzts198). Not applicable. The authors declare no conflict of interest.