funil hydroelectric powerplant on the grande … · main brazilian dams iii 178 funil hydroelectric...

FUNIL HYDROELECTRIC POWERPLANTON THE GRANDE RIVER

Author: Michael Sucharov (Based on reports and drawings furnished by SPEC).

Main Brazilian Dams III

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FUNIL HYDROELECTRIC POWERPLANTON THE GRANDE RIVER

1. INTRODUCTION

The Hydroelectric Powerplant of Funil is a low headrun of river powerplant and has a final installed capacityof 180 MW, is owned by the consortium ConsórcioBrasileiro de Aimorés - CBA which belongs to the Valedo Rio Doce Company and CEMIG, the State of MinasGerais Power Company. It is located on the Grande Riverupstream from Furnas dam and before São Miguel dam,in the municipalities of Perdões on the right bank andLavras on the left bank, in the state of Minas Gerais,Brazil. It is situated along the São Paulo - Belo Horizontehighway (BR-381), 395 km and 221 km respectively fromboth state capitals.

The catchment area is 15,153 km2 and the mean annualflow 341 m3/s. The reservoir covers 34,71 km2 at themaximum normal water level of El. 808.0 and impounds268.93 x 106 m3 of water.

The following studies were carried out on the Granderiver for hydroelectric development :• The first studies for the Hydroelectric Development ofthe Grande river, in the area called Funil were carried outin 1955 by IECO - The International EngineeringCompany.• In the 60's, the first systematic studies were made forthe Hydroelectric Inventory of the Grande River basin,and determined the partition of the falls along the river.These studies were made by a consortium of twocompanies, Canambra and CEMIG.• Pre-feasibility engineering studies and sitetopographical, geological and geotechnical investigationsin the hydroelectric area were carried out and forwardedin 1971 to DNAEE, the federal agency responsible forhydroelectricity.• The preliminary design was elaborated between 1990and 1992. Further studies to consolidate the preliminarydesign were made in 1996 with an alternative layout thatwould dam the river with a roller compacted concretedam (RCC) in the riverbed, and an incorporated spillway.The power circuit that included an intake, penstocks andpowerhouse was located on the left bank; because ofthe geology, a rockfill dam closing the right bank wouldhave had to be built.

To carry out the construction a consortium ofcompanies was formed and named "ConstructionConsortium for the Hydroelectric Powerplant of Funil".The companies were IMPSA, Servix/Mendes Junior,SPEC, ORTENG, DELP and ULTRATEC.

Main construction phases and schedules were:1. Start of works up to river diversion: 5 months;2. River diversion to 1st phase closure: 22 months;

3. Closure of diversion structure up to the start ofpower generation (1st unit): 3 months.

The first generating unit was put in commercialoperation in February 2006.

Optimization studies for the final design were carriedout by the Construction Consortium and a complementaryprogram of site investigations were made to cover areaswhere there was not enough geological information. Thisled to some important modifications of the preliminarydesign, listed below:

1. The concrete structures were relocated from theleft bank to the right bank in a more compact layout,with the following advantages:• It eliminated one of the critical paths of the constructionof the spillway in the river bed. This reduced the scheduleto 29 months for commercial operation of Unit 1, fromthe start of construction.• A reduction in the number of five radial gates to four, dueto a more favorable flow in the spillway stilling basin anddischarge channel.• Shorter lengths of penstocks with a smaller distancebetween the intake and powerhouse.• Only one upstream gantry crane would be necessaryfor maintenance of both the intake and spillway structuresas they would be adjacent.• The first stage cofferdam was eliminated by the use ofthe natural rock outcrop at El. 780.0 along the riverbankwith the new layout of the structures.

2. The main dam was designed with three sections,one of earthfiil, another of rockfill and a third zoned, forthe following reasons:• To minimize the required excavations in the riverbedand banks.• To use most of the excavation materials in the maindam.

3. The river diversion through a tunnel on the left bankof the Grande River permitted the construction works ofthe main structures at the same time as the tunnel, anda more flexible project schedule.

4. As a result of the modifications, the dam axis ofthe concrete structures was moved slightly upstream toimprove the layout.

2. LAYOUT

Funil's final design and construction can beconsidered as composed of two parts (Figure 1):

1. A main earthfill dam that bridges the Grande rivervalley, 50 m high and 420.0 m long at the crest; the rightend of the dam has a sharp right angle curve that abutsagainst the intake.


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2. The concrete structures that include the spillwayand intake; the first has four gates and a 7.356 m3/sdischarge capacity; the second is part of the hydraulicpower circuit, that includes, a short 50 m penstock and

the powerhouse that houses three turbine/generator units.The intake adjoins the spillway at a 15° angle, and inturn ends at the right rockfill dam.

Figure 1 - General Layout of Funil HPP

Photo 1 - View of Funil Dam from Downstream


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3. GEOLOGY AND GEOTECHNICS OFTHE FOUNDATIONS

3.1. Foundation rockThe foundation geology of the dam is made up of a

variety or rocks originating from the metamorphism ofamphibolites, gabbro and granulites and are denominatedhere as gneisses. Subsurface investigations carried outin the riverbed and banks, showed that below the alluviumlayer there was a seam of medium to very decomposedrock, highly fractured, with a permeability in the range of10-3 to 10-4 cm/s. The average thickness of this layerwas about 7.0 m and below it the quality of the rockmass improved and became adequate for the foundation,being competent and occasionally fractured with a lowpermeability of about 10-6 cm/s, which for practicalpurposes was considered impervious.

In the riverbed a 1 m horizon of extremelydecomposed rock made up of bands of feldspar andquartz, was found below another 5 m layer of sound orlightly decomposed rock.

On the left bank of the river near the main dam crestand the diversion tunnel, sound and lightly decomposedrock (D1/D2) was only to be found below a seam of 8 mdecomposed rock (D3/D4) which in some places was15 m thick.

On the right bank of the river, where the concretestructures are located, medium to very decomposed rockwas found in a much thicker seam than that on the leftbank, and reached 22 m along the crest axis, 12 m atthe spillway and about 15 m in the area of the intake andpowerhouse. Sound rock was found at lower elevationsin places where gneiss and diabase were in contact andalso in some locations where gneiss with bands of quartzand feldspar predominate, and which was also found inthe riverbed area.

At the end of the dam on the right bank, where theright rockfill dam is located, the decomposed rock seamhad a permeability of 7 x 10-5 cm/s, while in sound rockit was less pervious: 3 x 10-5 cm/s.

In the area of the intake, powerhouse and the overflowcrest of the spillway, the average permeability of the rockmass was 3 x 10-5 cm/s, practically the same as in themain dam foundation.

The strata of sound rock in the riverbed and in bothbanks were found to be occasionally fractured and theamount of fractures diminished with depth. Highlyfractured sections were not a common feature that couldbe found in the sound bedrock.

3.2. Residual soils and saproliteResidual soils

These soils occur in the right bank between colluviumand saprolite, and vary up to 3 m thick with the thickerstrata found higher up the river bank. The soils arecomposed of silty clay sand, micaceous, and yellow

brown when originating from amphibolite and biotitegneiss, and red silty clay when originating from diabase.

SaproliteThese soils originate from the foundation rock mass

and occur in both banks. On the right bank this seam isup to 45 m thick while of the left bank it reached only10 m.

The main origin of soils in the site area are fromgneisses and to a lesser degree from diabase and meta-diabase rocks.

Soil particle size when originating from decomposedgneiss was basically of silt and sand, with little clay andvariable colors, mainly with tones of grey, white and yellowindicating the rock origin.

At the base of the saprolite soils, near thedecomposed rock surfaces, particle size was coarse(medium to large) frequently mixed with fragments ofdecomposed rock. The average permeability of the soilwas 1 x 10-4 cm/s in the right bank and 4 x 10-4 cm/s inthe left bank. In general the soil resistance of saproliteby SPT tests indicated strengths above 10 blow countsand sometimes reaching over 30 counts.

3.3. Top soils (talus, colluvium and alluvium)These soils were found on the banks of the Grande

river and in the riverbed at the dam site.

Colluvium This type of soil occurs on the surface of the original

landscape on both river banks, with a thickness between2 and 3 m, but could be more than 4 m on the lower partof the right bank. It is made up of sandy clay below thesilty fraction, porous with a red brown colour. At the baseof the left bank and below the colluvium soil there was arock block strata up to 1.5 m thick and block size in therange of tens of cm. In some locations on the right bankthe colluvium is overlayed with diabase.

The resistance of this soil is in general equivalent toless than 10 blow counts by the STP tests, and reachedmore where there were fragments of rock or blocks. Thepermeability was between 10-3 a 10-4 cm/s.

Talus depositsThese deposits were found at the base of the left

bank with a height of less than 1 m. They were made upof rock fragments and blocks.

AlluviumIn the area of the main earthfill dam, alluvium was

distributed along the Grande river bed and the terrasseson the banks of the river. The depth of these depositsvaried between 6.0 and 12.5 m. On the upstream anddownstream side of the dam where the cofferdams arelocated, the alluvium was 6.0 m deep; in the cutoff areaof the riverbed it was 9.5 m; and in the central part of thedam it was 12 m.


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The alluvium layer on the right bank terrace was 8 mthick and on the left bank it was only 2 m and the coarseparticles varied according to the following locations:• In the riverbed there could be found mainly clean mediumsand, lightly micaceous, with 1.0 m of pebbles and rockblocks at the base of the layer.• In the riverbank terraces, alluvium was made up basicallyof fine silty sand, light grey in colour and mixed withcolluvium soil.• In the left bank downstream from the diversion tunnelportal there was a layer of rock blocks of sizes varyingbetween centimeters and meters in a 25 by 40 m area.

The resistance of the soil, based on SPT tests, waslow along the river terraces and high in the riverbed. Onthe right terrace the tests required 1 to 2 blow countsdown to 6.0 m deep. In the riverbed in general the testsrequired over 15 blow counts, with exception of theinvestigation SM-22 bore hole in the downstream cutofftrench where SPT tests required less than one blowcount, with a high permeability between 10-2 and10-4 cm/s.

3.4. Foundations of the StructuresMain Earthfill Dam and Right Rockfill Dam

On the right bank there is a layer of residual/saprolitesoil in the area of the right rockfill dam that reached40 m. A layer of colluvium 1 to 3 m thick covers theresidual soil. Between the altered soil horizon and soundbedrock there is a 20 m layer of decomposed rock(D3/D4). Part of the altered soil was removed to build theearth and rockfill dams. The saprolite seam of silty sandhad a resistance by the SPT tests requiring more than10 blow counts, and reaching more than 40 counts insome tests with a permeability of 10-4 to 10-6 cm/s. Thedecomposed layer below the altered soil had apermeability of 6 x 10-5 cm/s.

On the left bank where the main earthfill dam is locatedthere is a layer of 4 to 5 m of saprolite and overlaying itthere is a layer of 1 to 2.5 m of blocks of rock and colluvia.The earth dam was founded on the altered soil layer.

Some permeability tests in decomposed rock showedresults that were quite high, between 10-3 and 10-4 cm/s,requiring a grout curtain.

Between the alluvium and the foundation rock in theriverbed and the bank terraces there is a 5 to 12 m layerof decomposed and very fractured rock (F4/F5).

In this stretch the dam was based on the alluvium.About 70 m upstream from the dam a cutoff trench

was built intercepting the 9.5 m thick layer of alluvium,and reaches down to the decomposed rock surface below;a grout curtain was carried out along the cutoff to reducesubsurface flow.

The dam slope design considered a 0.04 g seismicacceleration.

Hydraulic Generation CircuitExcavations for the intake - powerhouse were carried

out along the right slope between the spillway and themain dam and included various soils and rocks, such ascolluvium, residual soil/saprolite, decomposed rock(D3/D4) and sound to decomposed rock (D1/D2).

Excavations were up to 35 m deep and blastingheights in decomposed rock were around 20 m deep.

In the intake and powerhouse area there were someweak areas where the decomposed rock excavationsand extreme fracturing had to be treated with gunite andanchored wiremesh.

The deepest excavations were in the powerhouse areadown to El. 747 and in sound rock they reached 33 mdeep along the axis of the units. The excavations of theright and left wall were done in 10 m vertical cuts with0.5 berms and where required, surface reinforcement waswith 6 cm thick gunite with fibers, anchored in a 2 x 2 mnet with 1" rebars 2.5 m deep.

In some places where the foundation rock surface ofthese structures was very fractured or decomposed, theweak area was removed and filled with dental concreteor grout and consolidation grouting was carried out.

Spillway and Stilling BasinThe specifications of the spillway and stilling basin

structures required that the foundations be of a goodgeomechanical quality. The spillway foundations were ofsound gneiss lightly decomposed (D1/D2) light to mediumfractured (F2). The gneiss foliation was 43° in relation tothe spillway axis and dips between 60° and the sub-vertical in the downstream direction. Apart from thefoliation there are two fracture systems that interceptthe dam axis, the first is 30° and dips sub-verticallydownstream while the other is 55° and dips between10° and 45° downstream.

The spillway excavations revealed bands ofamphibolite-biotite rocks and diabase rocks withdownstream sub-vertical dips.

For the right wall the excavations were the deepest inthe following materials: colluvium, residual soil/saprolite,decomposed rock (D3/D4) and sound to lightlydecomposed rock (D1/D2).

In the stilling basin after the removal of the alteredsoil, excavations were carried out in decomposed rock(D3) and sound to decomposed rock (D1/D2), with45° slopes 10 m high. Weak slope areas were treatedwith standard steel mats or fiber, gunite and rebaranchors.

At the bottom of the end upward slope of the stillingbasin there was an area with decomposed rock atEl. 760 that was treated with dental concrete, as well assome other areas. Dikes of diabase with a bigdownstream dip (70° to 80°) and decomposed near thecontact with the gneiss matrix didn't affect the excavatedslopes because of the slant relative to the side walls ofthe stilling basin.

The excavation of the soils above the maximumnormal tailwater elevation - El. 785 were 35 m high with


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slopes 1V:1,3H and 1V:1H, with 3 m berms in every10 m heights. Protection of these slopes was with plantedgrass and sometimes with gunite where grass could nottake hold.

Excavations in saprolite between El. 785 and thedecomposed rock in an area subject to tailwaterfluctuations has slopes of 1V:1.3H with berms of 5 mevery 10 m of height and protected with transition androckfill. In the intake channel the area of the slopessubject to the reservoir fluctuations were also protected.

In the same way as in the stilling basin, the slopes indecomposed rock (D3) of the spillway were less inclined(1V:1H) and were treated in weak areas with the standardgunite, steel wiremesh or fiber and anchored to the rockfoundation.

In sound rock excavations reached 17 m high withvertical cuts and 0.5 m berms, and the deeper cuts weremade in the stilling basin area.

The tailrace channel is in decomposed rock (D3) andat the end in saprolite. Where there was soil or verydecomposed rock the channel was over excavatedbetween 1 and 2 m below the bottom at El. 765 and filledin with rockfill for protection.

4. CONSTRUCTION MATERIALS

4.1. SoilsBased on studies before the preliminary design that

indicated two potential areas for materials for the damconstruction and denominated borrow areas 1 and 2, aprogram for investigations was elaborated to sample soilsfor laboratory tests. Both borrow areas were located onthe right bank of the Grande river at a distance of about1100 m from the dam axis.

The borrow areas had the same geologicalcharacteristics differing only by the thickness of the

layers. The top layers of colluvium had average thicknessof 2.0 m in area 1 and 2.9 m in area 2. In previous studiesit was classified as fine sand and secondarily as mediumto coarse sand with fractions of silt and clay, of mediumto high plasticity, and considered as MH material by theUnified Soil Classification System (USCS).

The underlying horizon is a residual soil with averagethicknesses of 7.5 m in area 1 and 6.2 in area 2. It wasmainly fine silty clay sand of medium plasticity, andalso classified as MH soils by the USCS.

The estimated volume of these soils was:1. Borrow Area 1• Colluvium 247,600 m³• Residual Soil 784,300 m³2. Borrow Area 2• Colluvium 459,600 m³• Residual Soil 549,100 m³

4.2. Coarse Grained Soils The prospection of sand and gravel deposits was

carried out in the river bed downstream from the damaxis. The depth of the deposits varied, reaching 12 mdeep as was the case of the one along the dam axis.The deposits were mainly of medium sand andsecondarily of coarse sand and gravel that were testedin the laboratory. The estimated volume of the depositswas 400,000 m³

4.3. Rock MaterialsBedrock materials were used as coarse aggregate

for concrete, rockfill for the dam and transitions and drainsand were obtained from the excavations for the foundationof the structures, the diversion tunnel and channels. Twotypes of rock were found: sound rock and decomposedto medium decomposed rock, and were used in the dam,cofferdams and various fills.


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5. DESCRIPTION OF THE MAINSTRUCTURES

5.1. River Diversion and TunnelThe construction of the civil works was done in two

stages. In the first the Grande river was kept in its naturalriverbed while the diversion tunnel was being excavatedin the left bank and the concrete structures on the rightbank. In the second stage with the upstream anddownstream cofferdams damming the river bed, the riverwas diverted through the tunnel.

The diversion tunnel structure was divided in theapproach channel, the control structure, the tunnel andthe outlet channel. The approach channel was 164.0 mlong, 20.0 wide and narrowing at the end to 14.6 m,excavations were in soil and rock. The control structureat the upstream portal has two openings for the closuregates 5.0 x 11.6 m. The actual tunnel is 211.0 m longwith a bottom rectangular cross section 11.6 m wide andsemi-circular at the top. The outlet channel is 142.5 mlong and 13.0 to 20.0 m wide from the tunnel to the endof the outlet. The diversion tunnel excavations were donein sound and lightly decomposed gneiss.

The upstream cofferdam was built by dumping rockfillacross the river flow at about 1 m above the water level.After dumping transition material and sealing, thecofferdam was raised with compacted soil up toEl. 776.20, which is the diversion elevation for a recurrenceriver flow of 20 years for the dry period of the year. Toprevent a backflow of water through the tunnel from thedownstream channel outlet, a downstream cofferdam wasbuilt similar to the upstream one with a crest at El. 773.00.The cofferdams were built with material from theexcavations for the foundations of the structures.

The following diversion scheme with the overtoppingof the partially constructed main dam was tested in thehydraulic models and used for the river diversion:

First Stage DiversionThe first stage river diversion of the Grande river was

made with the use of two natural septa that were left onthe left bank to protect the excavations of the diversiontunnel and the tunnel's intake and discharge channels.The leftover septa heights were derived from the ratingcurves made by CEMIG, based on two river water levelgauges installed nearby.

The maximum diversion design flow of 2,442 m3/s ledto water levels of El. 778.4 and El. 777.3 at the upstreamand downstream septa, and determined that both shouldbe left 1.0 m above these elevations: El. 779.4 and 778.3.

Second Stage DiversionIn the dry season of 2001, the second stage diversion

started after May, with the river flowing only through thetunnel. In the meantime the foundation treatment of theriverbed section and cutoff of the main earth dam were

being carried out. The compacted earthfill was raised upto the level of the cofferdam crests and the whole structurewas overlayed with a blanket of rockfill for protection. Inthe flood season the high river flows were dischargedthrough the diversion tunnel and overflowed the main dam.

During the dry season of 2002 the protection blanketof rockfill was removed to complete the construction ofthe main earth dam, with the river flowing again onlythrough the tunnel. The design flow for this stage was1,094 m3/s

5.2. Main DamThe construction of the main dam was planned to

use the maximum amount of material from theexcavations of the concrete structures and the diversiontunnel. Because of the geological-geotechnical conditionsof the foundation, the dam was divided in three typicalsections:one is rockfill with an impervious core, thesecond a mixed section of earth and rockfill and the thirda homogeneous earthfill. The crest of the main dam is atEl. 811.3.

The first section on the right bank, adjoining the intake,with a length of 25.0 m, is rockfill with an earth core andtransitions; the upstream and downstream slopes arethe same: 1V:1.3H; this section of the dam had itsfoundation on decomposed rock.

The second section toward the riverbed, about 80 min length, has a mixed section with rockfill on thedownstream slope with an inclination of 1V:1.8H and anearth slope on the upstream side, sand drains andtransitions (Figure 2). This section was founded ondecomposed rock and residual soil. Where the foundationwas on residual soil a cut-off trench 8.0 m wide wasexcavated into the decomposed rock below.

The third section is about 270 m long, from the riverbedto the left bank, and has a typical homogeneous earthsection, founded on an alluvium layer in the riverbed andgneissic saprolite on the left bank. The upstream slopeis 1V:2.1H and the downstream is 1V:1.9H from the crestdown to El. 785.0. From there on and until theincorporated cofferdam crest 12.0 m below, at El. 773.0the slope is 1V: 2.0H. In the riverbed a cut-off trench25.0 m wide had to be excavated through the 9.0 malluvium layer and the slopes of the trench were 1V:2Hin decomposed rock. The dam section has an internalvertical sand drain with a horizontal base.

For slope protection on the upstream side of the wholemain earth dam, where the reservoir water level varies, aprotection layer of graded sound rockfill was placed. Onthe downstream side protection of the slope from rainwas made with rockfill and transitions.

5.3. IntakeThe intake is located between the dividing wall and

the main earthfill dam. It is a concrete gravity structure44.7 m long and 34.0 m high, divided in three blocks.The upstream side has a 1V:0.1H slope and each block


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Figure 2 - Main Dam - Composite Section

Photo 2 - View of Funil Dam from Left Bank

has a sluiceway connected to a penstock that leads to apowerhouse turbine-generator unit. In each sluicewaythere is an emergency wheeled gate 5.8 x 7.0 mhydraulically operated. At 2.75 m upstream from thewheeled gate there is a second slot for stoplogs that willbe used for maintenance of the emergency gates. Thesluiceway flares hydro-dynamically from the gate widthof 5.8 m to an upstream width of 11.4 m which is dividedby a trashrack supporting beam 2.3 x 0.8 m, and hascurved flow surfaces. The intake upstream sill is atEl. 784 and the upper-sill is 14.52 higher at El. 798.52.

At the downstream side of the intake there is atransition from the 5.8 x 7.0 m center sluiceway sectionto a circular 7.0 m diameter concrete section in a 30o

elbow connecting to the penstock.There is a 3.0 x 2.5 m grout curtain and drainage

gallery, similar to the spillway, on the upstream side atEl. 779.0, 2 m above the foundation, that runs along thelength of the structure with an access through the dividingwall.

There are two 7,0 x 3,6 m rooms at El. 806.70, thathouse the hydraulic equipment for the intake emergencygate operations, with access by a steel ladder fixed tothe downstream side of the structures.

On the left upstream side of the intake is the "L"shaped concrete left guide wall that evens the flow in theapproach channel and abuts the main earthfill dam. Theconcrete abutment wall continues on the downstreamside to sustain the earth dam's horizontal load.

There are removable trashracks on the upstream sidewith two sections for each intake and are removed formaintenance with the auxiliary hook of the crest gantrycrane.

Figure 3 shows a cross section of the intake.

Figure 3 - Intake - Cross Section


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5.4. PenstocksThere are three 7.0 m diameter steel penstocks, one

for each unit that connects the intake to the powerhouse;both ends are horizontal and the difference in heightbetween them is 26.5 m with the centerline elevationsat El. 788.5 and the distributors at El 762.0. The lengthsof the penstocks are about 47 m, with small differencesbecause of the layout. In plan view the distance betweeneach penstock at the intake is 14.90 m, and increasesto 19.52 at the powerhouse, and as a result the sideunits' penstocks 1 and 3 are at opposite angles of about16º in relation to the straight center one of unit 2.

The geometry of the 7.0 m diameter penstocks, fromthe intake to the powerhouse is roughly: 1) 30º elbow inconcrete, that is part of the intake; 2) a 30º elbow insteel with a 17.285 m radius; 3) followed by a short10.5 m straight section; 4) and last, another elbow, 60ºin steel with a 17.38 m radius. At both ends the penstocksare anchored to concrete blocks. Figure 4 shows a profileof the penstocks.

The penstocks are all encased in an octogonal 8.6 mwide concrete structure on the upper side and rectangularon the bottom. Considering that the intakes are also lightstructures like the spillway, the concrete enclosuresaround the penstocks with 60% of the width of the intakeblocks, become structural additions to the stability ofthe Intakes.

The penstocks have pipe connections, just before thescroll cases, to feed the raw water systems for generaluse and generator cooling. These pipes are also usedfor dewatering the penstocks for turbine maintenance.

5.5. PowerhouseThe powerhouse is an indoor type with an overall length

of 92.37 m and divided into five major structural concreteblocks that house the three turbine - generator unit blocks:

19.83/19.52/20.52 m long; the 18.50 m long erection -service bay block and the 15.75 m unloading area block.Figure 5 shows a cross section of the powerhouse.

The layout assumed a maximum normal upstreamwater level and a minimum normal downstream waterlevel to assure a minimum positive head on the turbinesfor cavitation free operation, and as a result the center-line of the distributor was fixed at El. 762. Each unit drafttube outlet was divided in two 6.56 m wide dischargepassages by a 2.5 m pier, with slots for stoplog closure,for maintenance, operated by the draft tube gantry cranerated at 157 kN and with the runway on the downstreamdraft tube deck at El. 786.

The unit and service transformers are located on theupstream transformer deck at El. 786, which is the sameas the draft tube deck and the discharge platform.

The electric gallery is at El. 779.3, the mechanicalgallery at El. 774, the piping gallery at El. 767.7 and thepenstock gallery at El. 757.7; the erection bay is atEl. 774 and the equipment discharge platform at El. 786at the entrance to the powerhouse on the left side.

The station drainage sump and the unit dewateringsump are located at the end of the powerhouse on theright side and the pump room for both systems is atEl. 766.73. The bottom of the sumps are at El.746.23and El. 741.73.

The powerhouse has one overhead travelling cranefor the erection and maintenance of the turbine - generatorunits and appurtenances, with rails at El. 797 and travelsall the way from the equipment discharge platform to thepump sumps at the end of the generator hall. The craneis rated at 900 kN on the main hook and 250 kN on theauxiliary hook.

The draft tube discharges into the Grande riverbedchannel that was excavated in soil and rock and is315 m in length and 59 m wide.

Figure 4 - Intake/Powerhouse - Generation Circuit


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Figure 5 - Powerhouse - Cross Section

The 138 KV substation occupies an area 90 x 65 mand is located on the right riverbank atEl. 790 downstream from the dam axis

5.6. Dividing WallAdjoining the intake and the spillway is the angled

dividing wall, a concrete gravity structure that has atapered 15º plan configuration and connects bothstructures. To smooth out the flow to both structures,the upstream taper ends in a circular nose with a radiusof 7.94 m.

The wall is 26 m high, about 17.5 m in the flowdirection, and variable thickness. There is a shaft at thecrest for access to both drainage galleries by a verticalladder, and at the downstream level at El. 787.0, twometers above the rock foundation. The wall is not exactlya symmetrical structure because on the left side of thespillway, the 2.8 m side wall is embedded in a recess ofthe dividing wall. There is a 4 x 4 m shaft on the wall'sleft side as a fish passage from upstream to downstream;the reservoir water is fed into the shaft through a 1.2 msteel pipe; there is also a 7.0 x 5.5 x 3.5 m high electrical

equipment room at El. 806, with access by an outsidesteel stairs on the downstream face of the wall.

5.7. Spillway and Stilling BasinThe spillway is a gated surface type, with a capacity

to discharge the design flood of 7,356 m³/s. The structureis 64.6 m long with four 12.5 m bays and dividing piers3.0 m thick and based on a sound rock foundation. Thereare five concrete blocks for the four gates divided in two9.05 m side ones for ½ gates and three central 15.5 mones for 2 x ½ gates each. The radial gates are 12.5 mwide and 15.0 m high and hydraulically operated. Figures6 and 7 show the plan and profile of the spillway.

The structure is light with the ogee 8.5 m above thebase of the foundation rock. The refinement of thestructure resulted in a 7 m long extended downstreamfoot, 2.0 m thick that bears a large part of the load on thetoe at El. 780.0 where the piers also end. The horizontalfoundation rock surface of the main base of the structureis at El. 785.0 and 2.0 m above the 25.0 m wide excavatedrock trap adjoining the spillway. The approach channelis 5.0 m above at El. 788.


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Figure 7 - Spillway - Profile

Figure 6 - Spillway - Plan


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The ogee has a Creager profile with the sill atEl. 793.5. The crest is 5,5 m above the approach channeland discharges into a stilling basin that is 83.4 m longfrom the spillway toe to the basin end and 59.0 m wide.After the end of the spillway, the rock excavation surfaceis overlayed with a concrete slab 0.5 m thick, thatincreases to 1.0 m by the time it reaches the channelbottom at El. 758.0, and maintains this thickness untilthe basin end. The slabs are all anchored to the rockfoundation. The basin has an upward slope at the basinend 12.12 m in length and 7.0 m in height (1V:1.73H)and the lip is at El. 765.0.

The spillway crest is at El. 811.0 where there is aroadway to cross the river and the runway rails of thegantry crane. There is only one gantry crane for thespillway and intake and it travels all along the concretecrest structures up to the right gravity wall where thestoplogs of both structures are stored. The crane has acapacity of 200 kN on the main hook and 45 kN on theauxiliary monorail winch.

The reservoir load of the radial gates on the verticalspillway piers are absorbed by the concrete post-tensioned trunnion beams that are also post tensionedand anchored into the upstream side of the piers. Thecables were laid in a horizontal direction and the upstreamside has a tensioning chamber 3.0 m long at El. 797.5,the same elevation of the trunnion beams.

There are four 2,40 x 5,50 x 3,50 m rooms, one foreach gate, on the crest of each pier, that houses thehydraulic equipment to operate the gates.

The drainage gallery is at El. 787.0, and 2.0 m abovethe foundation, runs along the length of the structure withan access through the dividing wall. The gallery has a3.0 x 2.5 m section and the grout curtain was drilled onthe upstream side and vertical drains on the downstreamside. To certify that the uplift would be always low, thereis a top/bottom circular/rectangular 0.8 m drain parallelto the gallery and 8.5 downstream on the horizontal rocksurface, and another drain along the toe, 5.0 below. Thereare two drains under slope of the concrete basin surface,3.0 and 11.0 m below the spillway toe with 2% slopesfrom the center to the basin side walls, to prevent uplift.

The approach channel was excavated in soil androck at El. 788.0. The channel width diminishes from70 m to 40 m. Along the right spillway side wall whichcontains the first gate trunnion beam, the upstream partis designed with a curve to direct the approach flow andhas an "L" section to withstand the right rockfill damlateral loads. Adjoining the spillway and the right sidewall is the concrete gravity dam that joins the concretestructures to the right rockfill dam. This concrete structureis 22.0 m long at the base and 20.0 at the crest, 10.0 mwide and contains the stoplog storage shaft,7.5 x 14.0 m x 10.5 m deep.

Results from the hydraulic model tests showed thatinstabilities were noticed on the right side of the approachchannel that reached up to gate 4 of the spillway. To

reduce these instabilities a guide wall with a crest atEl. 811.0 was included in the design.

5.8. Right Rockfill DamClosing the dam on the right side by the spillway is

the small right rockfill dam that abuts against the concretegravity dam that extends on the right side of the spillway.It is made of rockfill and has an earth compacted core.

6. CONSTRUCTION SEQUENCE

The basis for determining the construction sequenceconsidered the following important aspects:• Compliance with the project schedule and allconstruction phases.• Coordination of excavations with the production of rockaggregate and earthfill for dam construction, to minimizetransport distances.• Concrete construction schedules not to interfere withthe electro-mechanical work and cause erection andinstallation delays.• Control of production volumes to reduce peaks andoptimize the use of manpower and equipment.

First Phase: The Grande River Flowing in theRiverbed

The following activities were carried out:• Stakeout of the jobsite.• Construction of the campsite and lodgings.• Construction of access roads.• Excavation of the diversion tunnel approach anddischarge channels, except the rock septa for cofferdams.• Tunnel excavation.• Excavation of the main structures on the right bank,except the rock septum at El. 780 along the riverbedthat was used as a cofferdam.• Start of concrete works, except the spillway.

Second Phase: Diversion Through the Tunnel• Removal of the septa located at the channel ends.• Construction of the cofferdams: upstream (El. 776.2)

Photo 3 - View of the Spillway and Powerhouse


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and downstream (El. 773.0).• Dewatering of the cofferdam area.• Excavation of the cutoff trench at the base of the maindam.• Grouting of the bottom of the cutoff trench.• Compacting of earthfill in the trench.• End of construction of the concrete intake tunnel portal.• Start of construction of the structures: erection bay andequipment discharge platform, powerhouse units 1 and2 blocks, intake units 1 and 3, right side guide wall, stillingbasin walls and slabs, left side guide wall and the gravitywall.• Start of the substation construction and second stageconcrete of powerhouse units 1 and 2.• Start of spillway concrete placement.• Construction of the earth dam on the right bank.

Third Phase: Diversion Through the Tunnel andRiverbed• Partial opening of the upstream and downstreamcofferdams, which were submerged and the floodspassing through both the diversion tunnel and the riverbed.• Continuation of concrete placement in the structures:erection bay, first stage concrete of powerhouse unit 1,intake units 1 and 3, right side guide wall, stilling basinwalls and slabs, left side guide wall and concrete gravitydam.• Continuation of construction of the substation andsecond stage concrete of powerhouse units 1 and 2.• Continuation of concrete placement on the spillway.

Fourth Phase: Only Tunnel Diversion• First stage cofferdams recovery.• Main dam foundation surface cleaning and treatment.• Construction of the main dam riverbed section andleft bank section.• End of right rockfill dam construction.• End of construction of all concrete structures andsubstation.• Sealing of the diversion tunnel with a concrete plug.• Reservoir filling.• End of architectural finishing and landscaping aroundthe powerplant.

7. TECHNICAL DATA

ReservoirArea at El. 810.70 38.32 km2

Area at El. 808.00 34.71 km2

Total storage at El. 808.0 268.93 x 106 m3

Total storage at El. 807.0 241.30 x 106 m3

Active storage 25.84 x 106 m3

Maximum flood level elevation 810.7 mMaximum normal level elevation 808.0 mMinimum normal level elevation 807.0 m

TailwaterMaximum flood level 787.40 mNormal level (3 Units) 771.52 mMinimum level (1 Unit) 769,03 m

River DiversionType TunnelLength of Tunnel 211.0 mSection: half circular/rectangular Ø 10.6 m

Diversion FlowsFlow Recurrence: 25 years: All 1st Phase 2,442 x m3/s 20 years: Dry Period 2nd Phase 1,094 x m3/s 50 years: All 3rd Phase 2,791 x m3/s

Tunnel Closure GatesQuantity 2 gatesWidth 5.0 mHeight 11.6 m

Power GenerationInstalled Capacity 180 MWFirm Output 99.77 MWh/h

Guaranteed Output (95%)Peak Load 180 MWOff Peak Load 29 MWAnnual Output 874,000 MW/hPeak Load 139,000 MW/hOff Peak Load 735,000 MW/h

Main DamType Earth-RockfillLength 420.0 mHeight 50 mCrest Elevation 811.3 mWidth of crest 8.0 m

SpillwayLength 64.6 mSpillway crest El. 811.0Overflow ogee sill El. 793.5Gate type and operation Radial - HydraulicSize and number of gates 12.5 x15.45 m-4 unitsDesign flood (10,000 years) 7,356 m3/sGantry crane capacity 200 kN/45 kNSpillway Stoplogs 6 sections/slotSize/number 12.5 x 2.4 m / 6 units

IntakeType of structure GravityLength 44.7 mNumber of blocks 3Intake crest El. 811.0


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Intake Emergency GatesGate type and operation Wheel - ServoNumber: 1 per Intake block 1 x 3 = 3Size: width x height 5.8 x 7.16 mGantry crane (serves Spillway as well) -Intake Stoplogs 3 sections/slotSize/number 5.8 x 3.0 m / 3 units

PenstocksNumber of penstocks 3Length 48Diameter 7.0 m

PowerhouseType IndoorLength 85.0 mOne - Overhead crane 900/250 kNDraft Tube Stoplogs 2 sections/slotSize/number2 sluiceways x 2 sections 6.56 x 4.55m: 4 unitsDraft tube gantry crane 160 kN

TurbineType KaplanRated capacity 61.5 MWCenterline of distributor El. 763.0Rated Flow 191 m3/sRated Head 35.3 mMaximum Head 39.0 mMinimum Head 32.5 mDesign Head 35.5 mOperating speed 150.0 rpm

GeneratorType Vertical axisRated capacity 63.2 MVAVoltage 10.0 kVFrequency 60 HzTransmission Line Connection Works1. Powerplant - Substation Interconnection3 x 138 kW Transmission Lines - 1 Double and 1 SingleCircuit: CAA aluminium cables - 400 m distance betweenstructures2. Substation Interconnection to CEMIG's DistributionSystemSectioning of the Campo Belo - Lavras Transmission Linenear the FUNIL PowerplantConstruction of 2 double circuits, 138 kV TransmissionLines - 2000 m distanceConstruction of 1 single circuit, 138 kW TransmissionLine - 19,000 m distanceTransmission Cables: CAA 170.5 mm² - LINNETLightening Arrestor Cables: 5/16" HS - Galvanized Steel

Project DevelopersOwners CVRD Companhia Vale do Rio Doce, CemigEngineer SPECContractor Consórcio Construtor Funil (IMPSA,Servix/Mendes Júnior, Spec, Orteng, Delp e ULTRATEC)

funil hydroelectric powerplant on the grande … · main brazilian dams iii 178 funil hydroelectric...

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