Tunnel two-expansion four-expansion excavation method

The invention relates to the field of tunnel excavation. The invention relates to a tunnel expanding excavation method. The method comprises IV-level and V-level surrounding rock tunnel construction methods and further includes an III-level surrounding rock tunnel construction method. The IV-level surrounding rock tunnel and the V-level surrounding rock tunnel construction methods comprise the following construction steps that an excavated tunnel is partitioned, and the excavation tunnel comprises a first part in the middle of an arch crown, a second part on the left side of the first part, athird part on the right side of the first part, a fourth part on the lower side of the second part, a V part on the lower portion of the third part and a VI part on the first part. According to the construction methods, double-side-wall partial excavation is adopted, and the excavation mode of first arching and then wall excavation has the advantages that the arch crown sinking is minimum, the horizontal displacement is s