Results of inspecting the temporary diversion tunnel of the Kurpsa hydroelectric station after completion of its operation

Abstract

The Commission of the Ministry of Power and Electrification of the USSR (Min~nergo) inspected the temporary diversion tunnel of the Kurpsa hydroelectric station, made with a lightweight lining, after its operation for 2 years and 8 months.The tunnel was originally designed with the following parameters:tunnel length, 634.1 m; inside cross section, 76 m=; type of lining, monolithic concrete with a thickness from 40 to 70 cm; roughness coefficient, 0.071; discharge capacity, ii00 m3/sec; concrete of the invert, grade 300, and of the walls, ceiling, and rings, grade 200.To accelerate construction, the design was revised for the purpose of lightening the lining.This resulted, as an experiment, in the monolithic concrete lining on a tunnel section 371 m long being replaced by a Gunite lining with concrete grade 300 with a thickness from i0 to 15 cm. The monolithic concrete lining was left in the invert, in the portal sections, and at places of tectonic disturbances of the rock foundation.The roughness of the surface for calculations by the Chezy-Manning formula was assumed to be 0.013 in sections with the concrete lining and in sections with a Gunite lining, 0.030 on the roof and 0.025 on the walls.The cross section of the tunnel in connection with the change in the type of lining was increased up to 85-100 m 2 to ensure passage of the design discharge.