UNDERGROUND STRUCTURE AND METHOD FOR CONSTRUCTING THEREOF

PURPOSE: An unsupported step underground structure equipped with an upper arch slab using a line backfilling mode and a construction method thereof are provided to reduce time and costs for construction. CONSTITUTION: A construction method of an unsupported step underground structure equipped with an upper arch slab using a line backfilling mode is as follows. An upper excavation part(2) is formed by evacuating ground. An earth retaining member(10) is installed in underground at a fixed interval. A slab installation part(11) is installed in the upper end of the earth retaining member. An upper slab(3) is installed between the earth retaining members. The upper excavation part fills soil between the earth retaining members. The soil between the earth retaining members is evacuated downward the upper slab. A lower bottom plate is constructed.