Methods of Repair Headrace Tunnel Invert – Repair of Deteriorated Headrace Tunnel by Using Slip Form – Paver Method

In Japan, hydro-electrical power plants are existing at approximately 1,800 places, but more than a half of such plants have been used over sixty years since the commencement of operation. Water channels that lead water, taken in from head areas, to hydro-electrical power plants are called the "headrace tunnel." The invert surface (concrete surface at the bottom of tunnel) of such headrace tunnels is normally curved at a certain curvature. The invert of headrace tunnel generally necessitates repairs because it has become worn or deteriorated due to conveyance of water over a long time period. However, it is required to complete repair work within a limited time period since it cannot be avoided to shut down operation of power plants when repair work is required. For such reasons, we executed a new method of applying new concrete overlay over existing concrete surfaces, smnothly cut by road cutter used in road construction, using slip form pavI iii1liud. Concrete was placed using slip form paver over curved surfaces to overlay the full width in a single pass. Repair of the invert surfaces of 3.6 m wide and 1,600 m long was completed within the water shutdown period of only 56 days. It can be concluded that this repair work was completed within one half of the average period, when compared with repairs by conventional methods in the past.