Construction of the Wloclawek development on the Wisla river

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    Yanush Belyakovski and Eryk Bobin'sld UDC 627.43. 001.8(438)

    By the end of 1969 the Wloclawek hydroelectric station will be operating to its full capacity,and the work on the first stage of the lower Wisla cascade will be completed. The advisability of the development site atWloclawek had been shown in 1955; the design was completed in the period between 1956 and 1959, and the project was ap- proved by the Polish People's Republic Council of Ministers Economic Committee in 1959. Preliminary work at the site, workers'camps,andcofferdams were completed during 1962-1964, and the mass concreting started in 1965. In 1968 the river was dammed and the flow was diverted through the concrete structures during construction. During the last years we have gained experience in heavy hydroelectric construction which allows us to evaluate the real perspectives ofhydro developments.

    The following parts constitute the Wloclawek hydro development: the earth and concrete dams, the power- house and navigation iock (Fig. 1).

    The average annual flow of the Wisla river at the hydro development is 930 m3/sec, and the minimum ob- served 140 mS/see. The spillway was designed for 9300 mS/see discharge capacity (the probability for exceeding this flow is 1%, the maximum observed flow of 8100 ma/sec happened in 1924) and had been checked for 11,150 mS/set flow (0.3%).

    The hydraulic fill river dam of local sands has a uniform cross section with 1 : 3 upstream and 1 : 5 downstream slopes and a total volume of 1.2 million m 3. The upstream slope is protected by a monolithic concrete slab and the downstream slope by rock.

    The mass concrete spillway dam consists of 10 gated bays. Each is equipped with individually operated gates. Energy dissipators and aprons are 102 m long and are designed for unit discharges of up to 40 mS/sec.

    The powerhouse annual output is 640 million kWh for an average river flow. There are 6 vertical units * with adjustable blade turbines (runner diameter 8 m) with 162 MW installed capacity; the total flow through the turbines is 2200 mS/sec. The open powerhouse is equipped with two 160-ton gantry cranes. Basic construction volumes at the development were as follows: earth moving 8 mill ion mS; plain and reinforced concrete 380,000 m3; structural steel and equipment erected 6300 tons; and power equipment (turbines and generators) 7200 tons.

    The foundation geologic conditions were nonuniform- characteristic forfolded formation. The water bearing tertiary layers contained artesian waters. The basic physical and mechanical foundation soil properties used in design were as foliows:

    for pliccene clays ~ = 13 ~ c = 0.1 kgf/cmZ;

    for brown coal ~o=18~ ', c = 0.15 kgf/cm2;

    elastic modulus E= 200 kgf/tm z.

    For such low shear indexes it was required to use a 30-mlong reinforced-concrete apron to ensure a reasonable sliding safety factor. Settlement of the structure was relatively great: the first section of the powerhouse before reservoir filling settled 10 cm with 4.5 kgf/cm z maximum pressure on the foundation; the general design settlements were about 20 cm. In view of uneven settlement and considerable relative displacement of powerhouse and dam, the deformation joints were made up to 10 and 15 cm wide.

    9 The turbines were manufactured at the S. M. Kirov Khar'kov Turbine Plant, and the generators were made at the "Uralglektrotyazhmash" at Sverdlovsk.

    Translated from Gidrotekhnicheskoe Stroitel'stvo, No. 7, pp. 27-30, July, 1969.



    Fig. 1. General arrangement of the Wloclawek development: (1) headrace; (2) tailrace; (3) dam ; (4) spillway; (5) powerhouse; (6) navigation lock.

    o ~ , .

    e. 2=

    o ~ "~

    l I c . . . . . . . . . o . . . . . . . J..oJ . . . . ) _ . c J . . . . . t . .5~, , i 500 ~O0 7OO 800 900 km

    Fig. 2. Schematic longitudinal profite of the lower Wisla cascade.

    Up to the present time, the Wloclawek hydro development is the largest complex in Poland built upon the rivers that flow through plains having complicated geologic conditions, Lacking previous experience, basic problems arising during design and construction had to be solved for the first time. The vast experience of the Soviet hydro construction on soft foundations had to be relied upon.

    Because oflimited space, below are only a few of the numerous complicated technical problems which had to be solved during construction:

    (a) determination of design flood discharges;

    (b) determination of spillway with powerhouse installed capacity and navigation lock dimensions;

    (c) general arrangement of the development and a general construction scSedule;

    (d) dewatering and lowering of water table at the construction site.

    The river damming is described in a separate article. *

    One of the main requirements in the initial stage of the design is the determination of a design flow for establishing the hydxaulic parameters of the development. The maximum flows for the design and checkup were correspondingly determined; the validity of considering the turbine discharges in total development discharges and the degree of safety in the design of water passages and equipment for the maximum discharges were also examined. At that time there was no established hydraulic construction classification in Poland: it was compiled later, on the basis of Wloclawek development design. It would be improper to transfer bodily the Soviet requirements, due to different possibilities as to the size of structures, smaller differences between the large and medium structures, and finally, due to the degree of river valley development and different hydrologic conditions.

    Adoption of a maximum possible discharge corresponding to a discharge with probability p = 0.01%, or p = 0.1% and design discharge p = 1% at the maximum flow level was discussed. The maximum discharge is spilled with an increase in upstream pool level which, for this case, was established as 1.2 m.

    At the same time the methods of maximum flow determination were studied, where, apart from different design approaches, difficulties were encountered due to the nonuniformity andincompleteness of the basic hydrol- ogic data. The hydrologic computations were made twice; in the initial stage and when the additional data for the middle and lower Wisla were obtained during the design. As a result it became possible to use 60 years of observed data for flood discharge design.

    The selection of Ql%as the design discharge for the development has been accepted everywhere. In the design of the spillway it was assumed that all gates would open without accidents, and out of six units at least four are operating.

    9 S -g~ge 630 of this journal.


    i - - - - - - "

    . . . . .

    Fig. 3. The site arrangement at the left bank excava- tion. Excavations for: 1) spillway dam; 2) powerhouse; 8) navigation lock; 4) earth cofferdam; G) cofferdam nose reinforced by concrete slabs; G) concrete plant; 7) basic equipment warehouse; 8) administration buildings; 9) wharf; 10) railway.

    For the maximum probable discharge Q0.a% = 11,180 m3/sec it was assumed that all powerhouse and spillway openings and equipment operate normally. The reservoir volume of 100 mill ion m s, which would allow an increase in the upstream level and, for a short period,flood wave,could transform considerably the flood peak at the development, which had not been taken into account.

    Design of the Wloclawek development and of other sites on the lower Wisla, continuing for more than 10 years, yielded some interesting observations for the Wisla hydrologic conditions. The maximum flows are repeated more often and the maximum flood discharges increase. Bank erosion and progressive development of the river basin seriously affect the normal and design maximum discharge values for various degrees ef probability. This effect, contrary to expectations, is c learly defined and calls for cor- rections of the maximum flow probability curve. On the other hand, this phenomenon will be regulated by reservoirs which are being created along the Carpathian tributaries of the Wisla. It is evident, however, that the hydrologic conditions on the Wisla are not constant,and it will be necessary to make a detailed study of the hydrologic and economic features for each new hydro development, with particular at- tention to the future changes in these features.

    As far as the Wloclawek hydro development is concerned, the spillway design was influenced more by the requirements of safe discharge of ice than by the max imum flow conditions. Operation of the dam during the winter and, particularly, the selection of clear width of spillway openings, caused some concern, as the Wloclawek development was looked upon as a pioneer lower Wisla development. The observation of structures and investiga- tions during the initial stage of operation will pen-nit checking the advisability of the measures taken at that time.

    The flood and ice passage conditions at the dam were checked on a hydraulic model. The results of the studies permitted taking into account the specific operational requirements at the dam during the ice break-up. The probability of ice pile-up in the reservoir had been studied too. The above condition is possible with flow below 4800 m~

    The capacity of hydroelectric stations in Poland depends on the type of peak loads in the system, their fre- quency, magnitude,and duration, and on the potential possibilities of water accumulation in reservoirs. The installed capacity for rivers on the plains in Poland is assumed to be less in the USSRfor the same conditions, and it is very nearly the guaranteed capacity. The latter is defined as the capacity for December with the plant working 4 to 6h per day and for 98% discharge. The additional limitation is the requirement of guaranteed capacity during other winter months equal to 0.9 of the December guaranteed capacity. The Wloclawek hydroelectric station is designed for four-hour peak loads in December, but the future Wisla plants will be designed for six hours pe~ day,and their installed capacities will be correspondingly lower. It should be added that in Poland the total water pondage hydro- electric station capacity (including automated HES) in 1970 will be about 650 MW, or about 4.840 of the country's total installed capacity.

    The difficult problems of peak load coverage and of guaranteeing the regulating and reserve capacities are being solved by construction of large automated HES.

    The navigation lock dimensions at the Wloclawek development were designed to correspond to the ealvisaged development of water transport along the Wisla. At present at Wloclawek the water transport accpunts for 200,000 to 250,000 tons annually, which is caused bya l imited navigable depth of the river on the stretch from Warsaw to


    Fig. 4. General view of the construction of the HES building at the headwater side.

    Torupya. In the future the river-borne freight in- crease will depend in the first place on the construc- tion of a deep navigable passage, During the devel- opment design from 1988 to 1 964 the freight estimates for the Wisla were changing constantly, At first it was considered that barges with tugs would dominate, and they require long lock chambers; the pushed barges require shorter chambers. Later it was suggested to build large locks for pushed barges in view of rapid river transport development reaching 10 million tons annually in 1978-1980, Detailed computations have shown that an increase of that sort is unrealistic, and the Iock capacity would not be used for many years, and a part of invested funds would be frozen. As a result, in 1964 it was decided to construct a lock for up to 6 million tons annual capacity. There is a pro- vision for constructing a parallel lock in the future.

    The general arrangement and construction scheduling depended maInly on topographic and geologic conditions of the valley. The location of the Wloclawek HES had been selected for the lower Wisla district (Fig. 2) but the specific position of the site and the structural arrangement had been deter-

    mined on the basis of geologic investigations and construction requirements. The powerhouse site was narrowly limited by the location of top layers of Poznan Pliocene clay, which is a comparatively uniform soil for the footing of the largest building with the deepest foundation. Other limitations were the spreading slide area on the high right bank of the river. Upstream and downstream from the chosen site were discovered stretches of banks with a lower sliding resistance.

    The relief of the site and transmission line location prompted locating the construction site on the level left bank. tn this case the favorable conditions for construction coincided with better geologic condition.~ and the single-stage construction schedule using a single cofferdam was a logical development. Location of the lock and spillway was no problem after location of the powerhouse, and a reasonably compact concrete structure arrangement was chosen. In this manner we have arrived at an almost classic arrangement for a development on a plain and a simple arrangement for construction discharges (Figs 1 and 3).

    It should be remembered, however, that the location of the navigation lock had been a subject of animated discussion during the design stage. It was proposed, for example, to place the lock in the river channel between the spillway and the earth dam. It turned out, however, that the proposed solution was impracticable due to the higher cofferdam and higher pumping costs, difficulties in construction scheduling, and inconveniences in the operation of the lock.

    The preliminary development design assumed the longitudinal cofferdam built as a double steel sheet piling wail. At time, it was a time-honored and proven solution having certain disadvantages due to the lack of steel sheet piles. Therefore, alternative solutions had to be studied. In 1961-1962, on the advice of the consultants from the ~Gidroproekt ~ (USSR) institute, an alternate solution was designed where the earth cofferdam had protective spurs at the corners. The upstream spur was selected on the basis , f hydraulic model tests.

    The cofferdam successfully withstood all floods and ice passages between 1964 and 1968 and remained undamaged. The adopted construction also ensured an easy and fast erection and, later, demolition of the cof- ferdam by excavators in eight days during the river damming. This type of cofferdam supposedly will be used during construction of other hydro developments along the Wisla.

    The excavation area protected by the cofferdam was about 18h,the elevation of powerhouse footing was 20 m and of the dam and the lock 10 m lower than the average river level. Under the difficult hydraulic and geologic conditions mentioned above,a complicated water lowering system was designed, consisting of one


    hundred I0 to 80 m deep pipe wells for draining the unpressurized water of quaternary as well as the artesian waters of tertiary sedimentary rock. During construction it became necessary to increase the number of drain holes in the quaternary rock.but at the same time it was found that the number of holes in tertiary rock could be decreased.

    In the design the total discharge of the water table lowering installations was determined to reach about 50,000 m s daily for the average and low river levels and about 80,000 m 3 for high river levels. The actual discharge had been correspondingly 13,000 and 20,000 m s daily. When the excavation for the first powerhouse section had been completed for the full height, there was a considerable seepage coming through the layers of early Miocene underlying the powerhouse foundation at the depth of about 30 m. The pressures in these layers were not lowered to a great extent ; when the seepage concentrated at certain points six emergency drains were drilled,and the flow stopped. The main holes were dewatered by pumps manufactured in Poland. To intercept the seepage in the slopes Soviet needle filter pumps were used.

    It was the first time in Polish practice that a number of technical problems had been successfully solved. The acquired experience will permit solving with confidence similar problems during construction of other devel- opments along the Wisla with smaller expenditures of economic and engineering resources.

    It is expected that valuable experience will be gained during operation of the Wloctawek development. Apart from the results of observations of the conditions and operation of specific buildings, structures.and devices, the results of observations of the unsteady flow in the tailrace and its effect on the river channel, flow regulation struc- tures and navigation conditions, and also observations of the silt movement and channel processes in the headrace and tailrace of the development will be of much value. The studies in this field are particularly important for the Wisla river flowing in a channel with nonuniform Jynamics chaxacterized by the Lokhtin number of less than 2.0.

    The above facts gain importance when it is realized that the development of the lower Wisla cascade will continue for a long period of time. In connection with this, there will be some developments withlow-levet tailraces, and their effect on the operating schedules of [he downstream stations will require, especially at the Wisla, very thorough investigation.

    To satisfy the most urgent needs and on the basis of the availability of engineering design, the most reasonable sequence for the cascade development (see Fig. 2) is as follows: Ciechocinek (regulating stage for Wloclawek), Vyszogrod (ice passage protection, bridge crossing) and Warsaw-North (for use of the capital).

    It is assumed that for the next 10 to 20 years the factor governing the lower Wisla cascade development will be, in [he first place, the satisfaction of local needs, which together with the overall national needs will have a determining influence on the order and time schedule for the lower Wisla development.


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