Consutruction and assembly works in the underground complex are combined with operation of the units at the Hoa-Binh hydroelectric station

For underground machine halls with a large number of units the areas of the assembly floors should be 1.5–2 times greater than for outdoor hydrosation powerhouses. Zones of the MH adjacent to the vehicular tunnels cannot enter into these areas; these zones should be regarded only as loading areas.

The technology of excavating the underground machine hall, including pits for the draft tubes, introduced at the Hoa-binh hydrostation can be recommended for excavating large chambers of considerable length.

The use of the given technical solutions when constructing underground hydroelectric station and pumped-storage stations in combination with fulfillment of par. 1 of the “CONCLUSIONS” will make it possible to reduce considerably the total construction time of underground machine halls and to provide start-up of all units.