Hydro power plant Matka Republic of Macedonia enlargement of surge tank:

ing. Emanuel Novák, 2005

mapThe surveyed territory is situated in a seismic active area with potential occurrence of earthquakes of 8oMCS (Mercaly, Cancany, Sierbergovy) in magnitude. The last severe earthquake occurred in August 1963, when the intensity reached 9o MCS.
The existing surge tank will be enlarged from its original capacity of 305 m3 to the required effective capacity of 1440 m3, the actual capacity is greater - 1962 m3.cross section The tank’s bottom will be situated at elevation 309.2 m, the top edge of the tank’s lining at elevation 323.0 m. The total volume of excavated rock will be approximately 1850 m3. Elliptical lining has been designed, including the bottom vault. The lining will be constructed of 400 mm thick shot concrete, reinforced with meshing and reinforcement steel, the bottom vault will be 500 mm thick. The lining will be constructed in a single step or step by step. The tunnel face will also be constructed of 400 mm thick shotcrete, again reinforced with meshing and reinforcement steel. For lining and other bearing structures, shotcrete (concrete) C30/37, steel S 500 (class of ductility „C“) will be used.
It is assumed that the rock will be excavated by blasting, using suitable explosives, systematically adhering to the smooth blast theory. In view of the tunnel height, it will be preferable to excavate the tunnel using the zoned cross-section technique, with at least two zones – callote and support. But a better solution seems to be splitting the cross-section vertically to 4 stages, so that it is not necessary to erect scaffolding for shotcreting works. Shot concrete should be applied in stages.
In view of the tunnel cross-section and seismic loads (9o MCS), 400 mm lining of elliptical shape with a bottom 500 mm thick vault has been designed. The lining will be reinforced with meshing and arches of reinforcement steel. It is assumed that wet shot concrete technology will be deployed. The reinforcement will use steel of shear strength fyk (or f0.2k) = 400 – 600 MPa, ductility class C by EN 1992 is essential. The fixing of lining and face reinforcement (as well as lining and walls of the entrance room to the surge tank, 400 mm thick) must have allowance for seismic loads, all joints must allow considerable ductility.

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