Construction method applied to ultra-shallow-buried tunnel in backfill area

The invention particularly discloses a construction method applied to an ultra-shallow-buried tunnel in a backfill area. According to the method, a detachable temporary supporting structure is adopted to be effectively connected with an existing formed primary supporting arch frame; the method comprises the following steps: S1, performing semi-finished product processing on a primary support arch frame and a detachable temporary support structure outside a hole; s2, according to the designed excavation footage requirement, the tunnel face of the upper step of the tunnel is excavated, and expansion treatment on the arch springing of the upper step is completed; s3, primary support arch frame construction is carried out, and meanwhile, installation of expanded arch springing I-shaped steel units is completed; s4, mounting a top I-shaped steel unit; s5, waist I-shaped steel units are installed; s6, the two adjacent steel arches are connected; and S7, the detachable temporary supporting structure is dismantled, a