Optimization of the construction sequence of the expanding excavation around Tunnel

Abstract

With the background of the construction of the Loushan Tunnel, Flac3D software was used to simulate three different expanding excavation sequence schemes. The simulation results were compared and selected, and it determined that Scheme3 is the best scheme. In the construction site, tunnel vault settlement and hance convergence were measured and compared with the simulation results. Conclusions are as follows: ①The final vertical displacement of Scheme.1 was greater than that of Scheme.2 and Scheme.3. In scheme 2, the horizontal displacement of the middle-upper part of the tunnel increased sharply after the excavation of the upper-right part. The maximum bending moment of the supporting structure of Scheme.3 was smaller than that of the other two schemes. In addition, the maximum bending moment in the whole process of expanding excavation transited smoothly, and it fluctuated the most in Scheme.2; ②When the upper-left part is expanded, the vertical displacement and bending moment of the supporting structure of the three schemes all increase greatly. In the actual construction, the most unfavorable factor is that the settlement detection value of the vault increases rapidly after the expanding excavation of the upper-left part; ③The construction sequence adopts Scheme.3, the settlement value & convergence value becomes more and more stable about 7 after excavation, the accumulated settlement value is 17.146mm, and the accumulated convergence value is 14.512mm. The field data is close to the simulated data, no accidents occur in the construction process, and no abnormal phenomena are found in the monitoring and measurement process.