A stable influence – building Zagorsk 213 February 2012
Institute Hydroproject, part of the RusHydro Group, is currently developing the Zagorsk 2 pumped storage project to help meet power demands in Russia.
The Zagorsk pumped storage project (PSP) was commissioned in Russia in 2000 to help solve regulation problems in the country’s power grid and to meet soaring electricity demand. In 2006, construction work started on the Zagorsk PSP-2 project, with an intended commissioning date of 2012 for the project’s first two units and final completion scheduled for 2014.
The designs of both pumped storage projects were completed by Institute Hydroproject, which is part of the Rushydro Group, one of the largest generating companies in Russia. Zagorsk PSP-2 is an unusual project in that it is being constructed entirely on a soft base and without suspension of activities at the first pumped storage project. The main parameters of the project are as follows:
* Capacity in generator mode 840MW, in power consumption mode – 1000 MW.
* Maximum head in generating mode 110m, in pumping mode 115.5m.
* Annual energy output –1000MkWh, annul power consumption 1350MkWh.
Institute Hydroproject examined 18 sites to discover the most optimum location for the project. The most promising proved to be in the Moscow Region where the deficit of load-following regulating capacity is about 1.5MkW. The most feasible solution was to build the project near the existing pumped storage project on the river Kunya at Bogorodskoye township. The site already had the necessary transport infrastructure, and some parts of the construction plant still existed. This, together with the absence of ecological limitations, enabled the construction of the project to begin quickly. However, the site was not without its problems. Investigations by Institute Hydroproject uncovered some issues that had to be addressed in the project design.
Hydrological and geological features
The region belongs to the central climatic district of the plain part of the European territory of Russia. The territory is in the forest zone with humid climate. Precipitations are unevenly distributed throughout the year. Institute Hydroproject has been carrying out systematic observation of the water levels and discharges in the Kunya river since 1967. The river length is 46km, and the total catchment area is 203km2. At the Zagorsk project site the catchment area is 194km2. Mean annual water discharge at the site is reduced to natural and is Q=1,43m3/sec, W.=43,13Mm3. The area is characterized by complex hydrogeological conditions. Groundwaters are located in bedrocks and in the Quarternary deposits. Alternating clayey and sandy strata dictated the design of a complex hydraulic system consisting of pressure and free flow water-bearing layers divided by the water-confining strata. Some geological processes and phenomena not previously encountered or sufficiently studied were identified at the site. They include high scale plastic deformations of massifs of clayey soils. On the right bank of the Kunya valley, this meant that the layer of paramonov clays (K1al3) across the front of the 1.5-2km the zone up to 200m wide was pushed on the middle Quarternary deposits. The origin and mechanism of gravitational deformations – the so-called «block landslides – are not clear. These features do not directly affect the structures of Zagorsk PSP-2, but still warrant further investigation for continued safe operation of the project.
Considering the fact the soft base of the main hydraulic units of Zagorsk PSP-2 have not been studied thoroughly using traditional methods, it would be reasonable to specify the physical and mechanical characteristics of the soils which form the base of the main units. The new way to calculate this is based on the new method elaborated for design definition of the physical and mechanical characteristics of the base, taking into consideration data on settlement of the buildings and deformation of the soft base.
For this purpose, the design of constantly active mathematical models of systems “structure-foundation” for the main hydro units is required, as well as for the water intake structure which is one of the most important facilities in the water retaining structure.
Using the series of iterative calculations with field data of settlement of the buildings and deformation of their foundations, it may be possible to define the physical and mechanical characteristics of the soils forming the base of the main units of Zagorsk PSP-2.
Zagorsk PSP-2 includes the following structures: upper pool; reverse intake incorporated into the body of the retaining dike of the upper pool; four lines of steel reinforced concrete open penstocks of inner diameter 7.5m; station block consisting of the powerhouse and assembly bay, transformer workshop, the rooms of start-up thyristor devices, reverse channel, service building; lower storage pool created through the expansion of the existing lower pool of Zagorsk; and transmission structures.
This is designed to hold 11.9Mm3 of water. The pool stability is provided by its special geometry. The dike has a maximum height of 40m, minimum height of 14m, the width of water area is 1090m, and it is 1870m long. The wide spread profile of the pool enables soil balance to be optimized due to the large excavation volume of the lower pool arrangment. Of interest is the procedure for first filling. During the flood, the first to be filled is the lower common pool, from there part of the water which flows through the units of the existing Zagorsk project is pumped into the upper pool up to elevation 255m. To compensate for any anthropogenic hydrodynamic effect, the intermorainal aquifer will be drained. This will help dewater sandy and sandy-gravel-pebble materials.
The upstream slopes have ratios of 1:3.5 (protected by reinforced concrete) and 1:7 (protected by sandy-gravel mixed with stone). The downstream slope is 1:2.5 protected by grass sowing and drainage.
Reverse Water Intake
This is a reinforced concrete structure uniting the inlet structure with four galleries to pass water into the tower for hydro-mechanical equipment. The intake works act as an intake with Zagorsk PSP-2 operating in turbine mode and as a water outlet when it is in pumping mode. It is incorporated into the body of the earthfill dike and its arrangement is similar to that of the intakes of the existing Zagorsk project and the Kruonis project in Lithuania. The intake height is 48m, the width along flow is 63.15m, across flow is 78.7m. Project designs incorporate two-layer drainage in the foundation base (a flat reinforced concrete slab 3m thick). Drained water will flow to the dry inspection gallery. Blanket drainage, 10m wide, is provided under the foundation slab in the zone of abutment to the penstocks, from where the filtered water is taken outside the water intake. Temporary stationary trashracks will protect the start-up units of Zagorsk PSP-2. The measures of surface water diversion and drainage near the powerhouse pit and the penstocks are of great importance for providing the slope stability, and retention of design geometry of the slopes during construction and operation.
Four open steel-reinforced concrete penstocks 800 m long and 7,5 m in dia are located on the slope between the water intake and the powerhouse. To provide the project stability, a special support structure – a pile zone over 20m deep – has been created to accommodate the concrete superstructures and steel shells with the reinforcing cages. They are fabricated at the construction plant of Zagorsk PSP-2 and transported by rail to the penstock site. The steel shells are also concreted in situ.
The powerhouse includes the machine hall, assembly bay, transformer workshop and transformer location area. The special dimensions of the powerhouse provide its stability. The machine hall length along the axis of the units is 106.5m, it is 45.24m wide and the height from the bottom of the foundation slab to the roof is 54m. The machine hall will house four reversible Francis pumps-turbines 6.3m in diameter and accompanying motor-generators. The powerhouse is located 834m from the axis of the water intake between two deep ravines. In plan, the powerhouse is incorporated in the left bank slope to enable pit excavation and to concrete the powerhouse under a pillar of soil, without the need for a fill cofferdam. The powerhouse pit has the large excavation volume – about 10Mm3 of materials, of which about 60% will be used as fill during construction of a dike at the upper pool.
Lower Storage Pool
The two projects will have a common storage pool located mainly in a vast floodplain (about 0.6x2.0km) opposite the town of Krasnozavodsk. The designers increased its effective capacity almost twofold by creating an artificial excavation at the bottom of the lower pool of Zagorsk PSP-1.
Due to a number of new design solutions, the Zagorsk PSP-2 project provides higher safety in comparison with the similar hydraulic units such as the Zagorsk PSP-1 and the Kruonis PSP.
In this project, new structural solutions have been developed and the new schemes of reinforcement have been improved and rationalized (with the optimal placement of reinforcement in the cross sections).
The next steps proposed for the project are:
¦ Erection of steel reinforced concrete penstocks with use of cast self-consolidating concrete mixture and modern reinforcement A500S;
¦ Compensatory transition penstocks adjacent to the water intake pool and the powerhouse of PSP-2 to be made of steel. At Zagorsk PSP-1 these are made of reinforced concrete and are subject to cracking;
¦ Pile-supported foundation of the penstocks to be fixed against the slope displacement with gantry (inclined) piles;
¦ Roller bearings of compensatory transitions to be used instead of rocking ones;
¦ Mounting of the one-piece elbow of the intake draft tube of the Zagorsk PSP-2 powerhouse has been provided, instead of being welded in place from the metal construction elements, etc.
Thus, on Zagorsk PSP-2 it could be said that new technologies of production have been developed as well as better and more reliable variants of drainage systems in back filling and units foundations.
Pavel Shestopalov, General Director, JSC Institute Hydroproject, Russia
Kirill Lobanov, a Chief Project Engineer, Zagorsk PSP-2 Project Director, Department, JSC Institute Hydroproject, Russia