the peixe angical hydroelectric development on the tocantins river

THE PEIXE ANGICAL HYDROELECTRIC
DEVELOPMENT ON THE TOCANTINS RIVER
Authors: Geraldo Martins Filho, Marcio Antonio Arantes Porto and Dionésio Werner Junior
Main Brazilian Dams III
THE PEIXE ANGICAL HYDROELECTRIC
DEVELOPMENT ON THE TOCANTINS RIVER
1. INTRODUCTION
The Peixe Angical Hydroelectric Development is
situated in the Tocantins River, on the border between
the municipalities of Peixe and São Salvador do
Tocantins, 320 km from the state capital Palmas, in the
South of the State of Tocantins, with an installed power
of 452 MW and a firm annual energy of 2,374 GWh. Its
owner is ENERPEIXE S.A., a special purpose corporation
composed as follows: 60 % owned by ENERGIAS DO
BRASIL (formed by the group EDP-ELECTRICIDADE DE
PORTUGAL) and 40% by the group ELETROBRÁS/
FURNAS CENTRAIS ELÉTRICAS S.A, for a total
investment of around R$ 1.6 billions.
The energy generated is transferred to the Brazilian
Electrical System by a 500 kV transmission line, through
the Gurupi Substation owned by FURNAS CENTRAIS
ELÉTRICAS S.A.
The first specific studies directed towards the
development of the hydroenergy potential of the Alto
Tocantins were developed in 1964 under the guidance of
the Centrais Elétricas de Goiás - CELG. The feasibility
studies for the Peixe Hydroelectric Development were
initiated by THEMAG ENGENHARIA in 2000.
The construction of the Peixe Angical HPP
commenced in April 2002 on the right bank of the
Tocantins River, although in August of 2002 the rhythm
of the job was reduced once the excavations for the
principal structures had been executed.
After FURNAS began its participation in the venture,
in October 2003, the work resumed its normal pace.
The following firms participated in this enterprise:
• Engineering services:
THEMAG Engenharia e Gerenciamento S/C Ltda.
• Civil construction and infrastructure services:
CCP - Consórcio Construtor Peixe, formed by the firms:
Construtora Andrade Gutierrez S.A.
Construtora Norberto Odebrecht S.A.
• Supply and erection of the electromechanical
equipment:
CEPAN, formed by the firms:
VOITH SIEMENS Hydro Power Generation Ltda.
BARDELLA S.A. Indústrias Mecânicas.
• Construction of the 138 kV and 500 kV transmission
lines:
Consórcio VA TECH ALUSA, formed by the firms:
VA TECH Transmissão Distribuição Ltda.
ALUSA Engenharia Ltda.
The energy characteristics of the development, as
determined by the studies carried out during the previous
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stages, were maintained with the planned installation of
three generator units, for a total power of 452 MW from a
rated net head of 24.30 m, and the maximum draw-down
of the reservoir limited to 2.00 m.
Figure 1 illustrates the location of the dam.
2. DESCRIPTION OF THE
DEVELOPMENT
The Peixe Angical HPP was built in the Tocantins River,
at the coordinates 12º 14' 16.6" S and 48º 23' 8.4" W. The
locations of the principal structures and the general layout
are detailed in the Figures 2 and 3, respectively. The power
plant comprises the powerhouse, with three Kaplan-type
turbines, situated in the right bank of the river. The spillway,
with nine radial-type gates, is adjacent to the RCC dam,
in the region of the original riverbed. The earth-rockfill dams
are located on the two abutments, one to the left and the
other to the right, for a total length of 5,755 m and a
maximum height of 39.00 m.
Table 1 presents the basic characteristics.
Table 1 - Principal Data of the Peixe Angical Development
3. GEOLOGY, GEOTECHNOLOGY AND
FOUNDATIONS
3.1. Geology of the Region and of the Dam Site
The area of insertion of the Peixe Angical HPP has
outcrops of the most ancient rocks of the crystalline
bedrock, designated as the Goiano Complex or the Basal
Complex, represented by the Araxá Group, comprising
a basal metamorphic unit with amphibolites, gneisses,
quartzites and garnet-biotite-muscovite schists, and a
superior unit with amphibolites, amphibolite schist, micaschists and quartzites.
Main Brazilian Dams III
Figure 1 - Location of the Peixe Angical HPP
Cenozoic era sediments cover the majority of the
regional units, constituted by detritus-laterite deposits
including sandy, silty and clayey sediments, in process
of laterization, alluvial terraces, basal conglomerate and
laterite crusts at the top and recent deposits represented
by alluviums on the margins of the water courses and
colluviums, constituted by roseate and yellowish sands,
clays and silts.
On the margins seated upon biotitic weathered
gneisses and residual soils there are extensive alluvial
plateaux, which include alluvial terraces in the form of
paleo-channels, with predominantly coarse sands and
gravels with local metric thicknesses in the range of
20 m, covered by sandy-clayey colluvial soil.
The local gneisses vary from biotites of a dark ash
colour, quartzites of light grey to white colour,
quartz-feldspar of light colours and garnet-biotite-gneiss
of roseate colour. The schistosity of the bedrock varies
from incipient to clearly defined, in the N-S general strike
(transversal to the Tocantins River) and dips
predominating between 35º and 65º W.
The bedrock appears almost totally sound and
coherent, with rare centimetre length stretches of more
weathered rock, whereas in the regions of the plateaux
the weathering is more intense, presenting a locally
residual soil of around 10 to 20 m thickness. The top of
the sound rock on the left bank, where the concrete
structures are planned, develops at depths of 10 to 20 m.
The degree of fracturing varies from slight to extremely
fractured, with the great majority of the fractures closed,
of rock to rock contact, some oxidized, and many
originating from the displacement along the schistosity
during the drilling process, which indicates a certain
fragility in these structures. The fractures vary from subhorizontal to vertical, with predominance of those that
are irregular and wrinkled, including flat, and some of
them grooved. Stretches of breccia material were observed
in some soundings, characterizing indications of faults.
The schists in the foundation of the left bank earth
dam, in the regions of stations 160 and 180, presented
permeable intercalations of carbonated and silicified rocks
respectively, of high hydraulic conductivity, constituting
an anomalous situation whose geological-geotechnical
outcomes could only be evaluated at the time of
executing the foundation treatments. With the exception
of these localized points, the bedrock is of low
permeability.
3.2. Geological, geotechnical and structural
characterization of the foundation
Rotary soundings confirmed the geometry of the body
of the limestone rock at Station 160, characterized as
marble, with a thickness of about 40 m, as being
approximately 25 m of marble with a saccaroid appearance
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and 15 m of recrystalized marble.
The body of silificated rock of Station 180 was also
investigated, and which, for practical reasons was simply
designated as "silexite", characterized by the presence
of alveolar shaped cavities, sub-horizontally elongated
according to the foliation, with an aperture generally
varying from 4 to 40 cm and with a variable length,
reaching up to 1.5 m, and proving to be a very highly
permeable rock.
Structural geology studies indicated that:
• the gneisses of the area were deformed by successive
phases of folding that developed and subsequently
affected the principal foliation. The dolomitic and
calcareous-siliceous type rocks are subordinate features
in the regional gneissic units, assuming the form of
discontinuous, inclined and subconcordant lenses with
the regional foliation, controlled by processes of
boudinage and by intersections of the regional foliation
with fault planes.
• the dolomitic and silexite marbles should conserve a
genetic relationship between themselves, it being
reasonable to presume that deformed zones of dolomitic
Figure 2 - Layout of the Principal Structures
Figure 3 - General Layout
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marble, subordinated to the gneisses, have been affected
by silicification caused by silica rich hydrothermal
solutions. This event was responsible for the generation
of silexites, leaving preserved irregular blotches of
dolomitic marble.
• subsequently, weathered aqueous solutions, possibly
acidic, must have promoted the karstification of the
dolomitic rock and of the dolomitic zones preserved in
the silexites, giving rise to the cavities formed by
dissolution. This explains the cavities and other karstic
features, as well as the internal surfaces of the gaps,
covered by a film of rough-white material.
3.3. Investigations carried out
lntensive prospecting studies, together with field and
laboratory investigations, were carried out to characterize
the hydrogeological conditions of the area of Station 160,
consisting of:
• Revision of the structural geology interpretation with a
view to identifying the mechanism of occurrence of the
layer of marble, its spatial disposition and continuity;
• Hydrogeological investigations with a view to
determining the hydraulic parameters of the water,
direction of flow, areas of recharge and discharge,
connections between different points of the aquifer,
including:
• Pumping tests;
• Tests with dies and tracers (to verify the connections
between points);
• Hydrochemical, physical and isotope tests;
• Rotary soundings and installation of piezometers in
the boreholes;
• Execution of deep pumping pits;
• Programme of geophysical surveys (seismic refraction
and electrical routing).
3.4. Foundation Treatments
The foundation treatments of the earth dams basically
consisted of a cut off trench to intercept the alluvial terrace
and a waterproofing grout curtain starting from the bottom
of the trench, about 20 m in depth.
The excavations of the cut off trench of the left bank
earth dam for exposing the residual gneiss soils, starting
from the left transition wall, as well as the work on the
grout curtain with its advance programmed in the direction
of the left abutment, up to the station 200 + 00, proceeded
normally, except for the stretches of the stations
155 - 165, and 175 - 182. At these locations the work
was halted before reaching the residual soil, as a result
of the presence of paleo-channels that had not been
identified in the basic design stage.
The increased depth demanded re-sloping the
excavations of the cut off trench and was reflected in the
job schedule, including delaying the beginning of the grouting.
On concluding the excavation, the drilling for grouting was
resumed, with the first perforations intercepting a strongly
artesian aquifer with flows reaching 120 m³/h.
The first attempts at conventional grouting in this region
were unsuccessful, due to the injected materials being
driven back to the surface by the artesianism, or as a
result of the high takes of solids experienced, without
attaining the closure of the grout injected boreholes.
The soundings executed to investigate the supposed
anomalies detected, respectively, the bodies of
carbonated and silexite rock, the former petrographically
characterised as dolomitic marble, with the presence of
karstic features.
3.5. Treatments of the stretches of silexite and
dolomitic marble
A specific treatment project for the silexite area
consisted of five rows of grout holes and the construction
of a concrete slab over the outcrop of silexite at the base
of the cut off trench.
The treatment in the region of station 160 consisted
in the execution of a grout curtain and, specifically in
the region of the layer of marble, the execution of a secant
pile cut off, 1.80 m in diameter, using large drills capable
of perforating the layers of silexite in the transition zone
and penetrating the marble. The solution of the secant
piles, as indicated in the executive planning, was
employed in the construction of a watertight diaphragm,
both in the transition zone and in the rock, in order to
avoid the beginning of piping processes.
Due to the need for maintaining the grouting equipment
installed within the cut off trench in the area of Station
160 and the brief time available for constructing the earth
embankment of the dam before the start of the rainy
season, the dam embankment was displaced
downstream.
In order to permit the construction of the secant pile
cut off, even after the impoundment of the reservoir, it
was planned to construct a cofferdam upstream of the
dam, so that the drilling for the pilings could be executed
from a platform situated at El. 258.00 m.
Complementary treatments of the areas considered
to be anomalous.
The stretches of exploratory curtain whose drillings
presented three or more stretches with a grout absorption
greater than 50 kg/m within a space of 30 m were
considered to be anomalous areas. In addition,
geophysical surveys with electro-resistivity were
performed in longitudinal and transversal sections to the
axis of the dam, to identify any permeable features
present in the foundation.
Based on this criterion, ten areas were investigated
with rotary soundings and water tests, whereas only five
areas were submitted to reinforcement of the cut off with
the same treatment of the area of station 160.
Four soundings were performed in the area of the
station 177 which revealed the presence of carbonated
gneiss with lenses of marble of 0.1 to 1.0 m thickness.
Nine reinforcement holes were executed in the existing
cut off plus two verification holes, with satisfactory results.
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4. HYDROLOGY, HYDRAULICS AND
ENERGY STUDIES
• Net reference head
• Net design head
4.1. Energy studies
The energy and operational studies had the objective
of verifying and updating the definitions of the feasibility
phase, as well as to advance in the detailing of the
operational conditions of the power plant.
4.3. Minimum dispatch and peak guarantee
In times of low hydric availability the power plant must
be able to generate the energy corresponding to its
installed power during peak hours and still operate outside
the peak, generating its minimum capacity.
The integration of the Peixe Angical to the Brazilian
interconnected system consists in the connection to the
basic interconnecting North-South network, Gurupi
substation, by means of a simple circuit 500 kV
transmission line with a length of approximately 92 km.
For the performance of the electrical studies the data
employed were those of the Brazilian interconnected
electrical system, available from the ONS (National
Operator of the System), in the configuration
corresponding to the year 2004, with the North-South
interconnection already containing two circuits of
500 kV, interconnecting the substations of Imperatriz in
Maranhão (North-Northeast system) and of Serra da
Mesa, in Goiás (South-Southeast System). The premise
of the studies performed consisted in the need to exercise
the minimum electrical impact on the interconnected
system (basic network), in accordance with the
procedures of the ONS network.
4.2. Background
The tender documents for the concession and
exploitation of the Peixe Angical HPP defined, based on
the feasibility studies, the optimum development of the
site, as follows:
• minimum installed power
450 MW
• maximum normal water level
263.00 m
• minimum normal water level
261.00 m
Still based on the feasibility studies, the ANEEL fixed
the firm energy and power of the development, after its
complete motorization, to the guaranteed level of the
interconnected system, as follows:
• Mean firm energy
271 MW
• Firm power
417.3 MW
The feasibility studies also defined the following design
parameters and elements:
• Local firm energy
286.41 MW-mean
• Mean energy
309.84 MW-mean
• Capacity factor
0.64
• Reference head
23.80 m
• Net design head
26.07 m
• Number of generator units
4
After the conclusion of the feasibility studies the
number of generator units was defined as three, in order
to optimize the development and, based on new
hydrology information, a new flow rating curve was
established in the tailrace channel, .
The monthly simulations permitted assessing the
impact of the new rating curve upon the energy production
results and the characteristic heads of the development.
The same simulation model used for the feasibility
phase, that is, the Model H of the THEMAG, was updated
with flow series up to 1996 for all the power plants, also
including the Southern generation system with those
already represented by the South-eastern/Centre-West
and North/North-eastern systems.
The energy results obtained were:
• Local firm energy
288.4 MW-mean
• Mean energy
307.5 MW-mean
In addition to these results, new reference and design
heads were calculated based on the same criteria applied
in the feasibility phase, that is, a monthly head with a
permanence of 95% of the time, for the reference head,
and a mean head weighted by the energy generated during
the critical period, for the design head.
The results obtained were:
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24.20 m
26.40 m
4.4. Hydrology
The hydrographical basin of the Tocantins River is
predominantly affected by the rainfall producing
mechanisms incident on the North and North-eastern
regions. Notable among these is the Intertropical
Convergence Zone (ITCZ) which in this region consists
of the convergence of the trade winds of both
hemispheres. Dynamically, the ITCZ is associated with
a low pressure band and the convergence of the flow in
the low levels of the atmosphere, which promotes the
conditions favourable to the ascending movement and
the consequent presence of clouds and precipitation.
As a rule, the ITCZ migrates every season from its
most northern position, approximately 14º North in AugustSeptember, to its most southern position, approximately
2º South, in March-April. Its displacement and intensity
condition the quantity of rain falling on the region.
One of the interesting aspects associated with the ITCZ
is that it is situated in a band of oceanic dominance.
Therefore, it is reasonable to expect the existence of a
relationship between the temperature anomalies of the
oceanic surface in this band and the rainfall in the regions
of the continent or, more specifically, in the Tocantins basin.
In general, the mean annual temperatures in this
region tend to diminish as the latitude increases, varying
from 25ºC in the North down to 21ºC in the boundaries
with the State of Goiás.
Although the mean temperatures are high, the
continental position of the area makes the night-time
temperatures comfortable in comparison with those of
Main Brazilian Dams III
the daytime. The thermal amplitudes are greater in the
localities situated at higher altitudes (above 600 m), with
the opposite occurring in the flat areas.
The mean annual sunshine in this area varies around
2,400 hours (daily average of 6.6 hours of sunshine).
During the month of July, the period of maximum
sunshine, the monthly values remained around 320 hours
(average of 10.3 hours per day). In the month of January,
the monthly mean is around 150 hours (4.8 hours/day),
corresponding to the period of greatest rainfall.
The rainfall in the region is marked by the rainy season,
hot and damp, which alternates seasonally with the
relatively dry and colder season. The rainy season
commences between October and November and
extends to March, on occasions reaching the beginning
of April. The dry season begins between May and June
and extends until September.
The mean annual precipitation, over the whole area,
is around 1,500 mm, with the hydric requirements of the
dry season being compensated by the precipitation in
the rainy season.
A few areas of the region present a mean annual
precipitation of around 2,000 mm, under the direct effect
of the orographic relief, while other areas offer a mean
annual precipitation of around 1,250 mm.
With regard to the intra-annual regime, the Gurupi
station is utilized as being representative of the area,
observing the presence of two fully distinct periods: one
rainy period, from November to March, concentrating 77%
of the annual total, and the other quite dry, from May to
September, with barely 5% of the precipitation.
4.5. Maximum flood
During the feasibility studies, analyses were developed
with the objective of defining the design flood of the spillway
and of the diversion stage. It should be mentioned that the
maximum flows of the years 1979/80, 1986/87, 1989/90,
1991/92 and 1993/94 were not employed due to the lack
of data during the flood period.
4.6. Spillway design flood
Considering that the values of Table 3 refer to daily
mean flows and not to instantaneous flows at the peak of
the flood, a Fuller correction coefficient was applied, which
resulted in the maximum instantaneous value of
42,500 m³/s. The spillway was designed for a maximum
flow of 37.044 m³/s, with the reservoir operating at elevation
263,00 (maximum normal water level) and at 42,500 m³/s
(maximum design flood) with the reservoir at the maximum
elevation of 265.21 m, admitting, in this case, the spilling
contribution of the overflow concrete dam.
4.7. Diversion flow
The diversion flood was fixed at the value of
14,550 m³/s, corresponding to the fifty year flood of the
regional statistical study. This flow, however, is only
justified for the works that continued through at least
one rainy period comprising the months from December
to March. For those known to be restricted to the dry
period, this value can be reduced, particularly when they
are limited to the driest months between July and
September, reaching a minimum value of 1,780 m³/s in
the month of August.
The estimate of the fifty year floods during the dry
months considered that these floods would be composed
by two distinct portions: one fixed portion of 1,200 m³/s,
corresponding to the maximum outflow from the turbines
of Serra da Mesa, and a variable portion corresponding
to the flow generated in the intermediate basin between
Serra da Mesa and Peixe Angical (drainage area =
74,712 km²). Tables 2 and 3 contain the hydrometeorological data of the Tocantins River basin.
Table 2 - Hydro-meteorological Data
Table 3 - Mean Daily Flows During Flood Peak - Gumbel-Chow
5. PRINCIPAL STRUCTURES
Figures 2 and 3 illustrate the principal characteristics
of the structures and their general layout, which are as
follows:
Total lenght of the dam along the crest at
El. 266.00 m is 6,148 m.
Erection area contiguous to the powerhouse, in
reinforced concrete, with a width of 56.63 m. allowing
the erection of the hydrogenerator units, with a unit
commencing generation every three months;
Tailrace channel excavated in rock, with bottom at
variable elevations, in a ramp of 1V by 6H from the
El. 207.00 m to El. 230.00 m (approximate elevation of
the rock top);
Fish transposition system constituted by a structure
of the ladder type, interconnecting El. 260.00 m to
El. 233.50 m;
138 kV / 500 kV substation situated around 1,100 m
downstream of the powerhouse, in the right bank,
occupying an area of 51,523 m²;
Transmission line with a double vertical circuit and a
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simple vertical circuit of 138 kV, with a length of 894 m
and band-width of 41 m (two parallel circuits)
interconnecting the power plant to the substation,
containing 8 self-supporting towers of the sail type,
tubular-type anchorage and foundation;
Simple circuit transmission line of 500 kV, with 91 km
+ 933,57m in length and a bandwidth of 70 m, linking the
Peixe Angical power plant to the Gurupi substation in the
town of Gurupi, integrating the North-South transmission
system; reservoir with flooded area of 294.10 km², at the
maximum normal water level of El. 263.00 m;
The layout permits the future construction of the
navigation lock and channels for a convoy of
200 m x 24 m, with a draft of 3.50 m .
5.1. Dam
In the Peixe Angical Hydroelectric Power Plant the
dams are of the earth - rockfill type and in Roller
Compacted Concrete (RCC), the latter located in the
riverbed, with a total length of 545.30 m (including the
left transition wall). The gravity-type left transition wall, is
constituted by the blocks BL-28, totally in concrete
compacted by vibrator (VCC) and BL-27B, up to
El. 237.00 m in conventional concrete from that elevation
until the crest (El. 266.00 m) in RCC, located at the end
of the concrete dam and enfolded by the clay-core rockfill
dam (earth dam of the left bank).
The transition between the right bank dam and the
erection area (length 420 m), is constituted by the earth
and rockfill dam, with a composite section involving the
structures of the erection area.
The embankments are composed by clay cores,
vertical and horizontal filters of sand and rockfill in selected
stone material. The principal data of the dams are
described in Table 4 and the Figure 4 shows the section
of the earth-rockfill dam.
Photos 1 and 2 depict the construction of the earthrockfill dam of the right bank in 2003 and 2006; Photo 3
the same dam concluded.
Table 4 - Principal data of the dams
Figure 4 - Earth-rockfill dam of the right bank
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5.2. Spillway
The structure is of the surface type, with gates, of
reinforced concrete with a Creager profile, equipped with
nine radial gates of 22.82 m in height by 17.00 m in
width, designed for a maximum flow of 37,044 m³/s, with
the reservoir operating at the El. 263.00 m (maximum
normal water level). The dissipation pool with its bottom
Photo 3 - Earth-rockfill Dam of the Right Bank Concluded
excavated at El. 222.50 m is lined with reinforced concrete
over 29% of the theoretical length of the flip bucket, limited
by walls of the gravity type, with dimensions of 218 m
width and 46.50 m length.
Table 5 shows the principal data of the spillway / sidewalls, while Figure 5 shows a plan view of the spillway.
Photo 1 - Construction of the Earth-rockfill Dam of the Right Bank
in 2003
Photo 2 - Construction of the Earth-rockfill Dam of the Right Bank
in 2006
5.3. Water Intake
The water intake is of the gravity type with three
hydraulic oil operated fixed wheel gates, with dimensions
of 6.80 m width and 16.60 m height. It is associated with
the powerhouse of reinforced concrete, under the reference
Table 5 - Principal Data of the Spillway
Figure 5 - Plan View of the Spillway
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head of 24.30 m and flow corresponding to 2,064 m³/s,
in a typical layout for low-head power plants. Table
6 contains the principal data of the water intake.
Figure 6 shows the plan view of the water intake and of
the powerhouse.
Table 7 - Principal Data of the Powerhouse
Table 6 - Principal Data of the Water Intake
5.4. Powerhouse
In January 2004 the concrete placement commenced
at the indoor-type powerhouse with a total length of
53.65 m. This building houses three generator units, and
each block of this unit totals a perimeter of 98.18 m.
Table 7 shows the principal design data of the
powerhouse.
Photo 4 depicts the powerhouse during construction
and Photo 5 a view of the powerhouse-generators hall.
Photo 4 - Powerhouse during Construction
Figure 6 - Plan View of the Water Intake and of the Powerhouse
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Table 8 - Data on the River Diversion
6. CONSTRUCTION OF THE PEIXE
ANGICAL HPP
Photo 5 - View of the Powerhouse-generators Hall
5.5. River Diversion
In order to permit the construction of the concrete,
earth and rock structures, the Tocantins River was diverted
from its normal course in two different phases of the job.
The first phase involved the placement of cofferdams
starting from the right bank, and restricting the riverbed
as much as possible. This restriction was limited to the
condition resulting in maximum mean velocities of less
than 5.0 m/s in the most confined section.
In the second phase the river was diverted through
three of the spillway bays, with their sills still at the
El. 232.0 m; this being below the design elevation (see
Photo 6).
Photo 6 - Diversion through the Lowered Spillway Bays
After the closure of the natural trough of the riverbed
and the appropriate raising of the RCC dam, the flow
through the lowered bays (two at a time) was interrupted
by means of the radial gates and the stoplog gate
assemblies, permitting the concrete pour of the ogees
at their final elevations.
Each phase of the first and second stages of the river
diversion was sized for the maximum flows with a
50 year recurrence, taking into consideration the duration
of each event.
Table 8 shows the principal data on the stages of the
river diversion.
6.1. Sequence of the Construction
The present sequence is restricted to the principal
stages of the construction, which are illustrated in
Figures 7 to 11.
6.2. Quality Control of the Peixe Angical
Hydroelectric Power Plant
The quality control programme covered the controls
over all activities associated with the works of the Peixe
Angical HPP, comprising the planning/scheduling,
construction, oversight, tests/reception of the structures
and the environment.
The quality control programme exercised the control
over all the materials employed in the works, as well as
the structures built, with a view to verifying their conformity
with the standards, specifications, operational procedures
or applicable practices or other requirements contained
in the technical specifications of the civil works,
electromechanical erection and the environment, with a
view to addressing the requirements of the integrated
management system based on certification standards:
NBR ISO 9001 and 14001.
6.3. Problems encountered during the construction,
special solutions adopted
The principal problem encountered during the
construction of the Peixe Angical HPP was the
occurrence of a dolomitic marble body located in the
foundation of the Left Bank Earth Dam (LBED) and
identified during the excavations and foundation
treatments of the dam.
During the excavations for the cut off trench for the
exposure of the residual gneiss soils in the region of the
stations 155+00,00 and 165+00,00, an existing
paleo-channel was identified that had not been detected
in the basic design stage.
The initial geological/geotechnical mapping of the
exposed foundation failed to indicate, at the beginning,
the existence of any relevant anomaly.
The initial drillings for the grout curtain in this stretch
intercepted an aquifer with high pressures and flows of
the order of 120 m³/h.
The first attempts at conventional grouting in this
region were unsuccessful due to the injected materials
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1 - Commenced excavation for concrete structures and for
the approach and discharge channels.
2 - Commenced excavations, foundation treatment
and construction of the earth and rockfill dams.
3 - Commenced placement of the pre-cofferdam, dewatering
of the enclosure and raising the height of the 1st phase
cofferdam.
4 - Conclusion of rock excavations for the concrete structures.
Figure 7- Construction Sequence - Year 1 (2003/2004)
1 - Commenced foundation treatment and concrete placement
of spillway, water intake, powerhouse, erection area
and central wall.
2 - Construction sequence of the earth dams of the left
and right banks.
3 - Foundation treatment and raising the height of the dam
in the riverbed of the 1st phase dewatered stretch.
4 - Execution of the left bank enfolding wall.
5 - Commenced civil works of the substation.
Figure 8 - Construction Sequence - Year 2 (2004/2005)
1 - Continued execution of the concrete structures.
2 - Commenced work on the auxiliary cofferdams
of the 2nd phase.
3 - Continued the services of the earth dam of the left bank.
4 - Partial removal of the 1st phase cofferdam; commenced
2nd phase cofferdams and river diversion through the
lowered sills of the spillway.
5 - Conclusion of the civil works in the substation.
Figure 9 - Construction Sequence - year 3 (2005) before the River Diversion
296
Main Brazilian Dams III
1 - Dewatering of the coffer area, cleaning and foundation
treatment and commenced construction of the concrete
dam in the riverbed.
2 - Progressive closure of the lowered spillway bays and
concrete placement in the ogees.
3 - Concluded the works of the earth and concrete structures.
4 - Concluded the electromechanical erection in the
substation.
Figure 10 - Construction Sequence - Year 3 (2005) after the River Diversion
1 - Filling the reservoir.
2 - Commissioning the generator units.
3 - Commenced commercial generation. (June 27,2006)
Figure 11 - Construction Sequence - Year 4 (2006)
being forced back to the surface by the artesianism or to
the high absorptions of solids verified.
As a result of these anomalies it was decided to carry
out rotary soundings at the locale.
The petrographic analyses of the core samples
indicated the presence at the site of a carbonate rock,
classified as being a dolomitic marble with karstic
features.
During the months of July/August of that year,
soundings were scheduled at the site for the purpose of
characterising the dimensions, attitudes and extension
of the anomaly.
In order to address the diverse sounding campaigns
requested by the designer, approximately 3,586 m of
drillings were executed, against 900 m of perforations
executed in the feasibility studies and basic design stage.
The first investigations characterised the great difficulty
of drilling the marble bedrock existing at the site, with the
observation of decomposed layers alternating with more
consistent materials, losses of composition, low core
recovery, existence of cavities, total loss of the drilling
fluid, abrupt variations of the rocky top and great instability
of the walls of the drill- holes.
These conditions then revealed the high complexity of
the anomaly, seriously hindering the comprehension of
the geological/geotechnical model of the locale.
The first solution determined for the treatment of the
anomaly prescribed that the treatments to be performed
at the site should only involve injections of grout and mortar
over the entire extension of the anomaly. The grouting
should be made possible by lowering the water level at
the site.
It was determined that the lowering of the water table
would be obtained by drilling several large diameter
pumping pits. The pumping pits were executed and were
unsuccessful due to the instability of the drillings and the
high flow through them which failed to allow the necessary
lowering.
297
Main Brazilian Dams III
By compressing the job schedule and considering the
need to confine the existing aquifer, in order to try to make
feasible the grouting at the site, a construction program
was adopted, consisting of the following:
• Backfilling of the excavations already made, with
compacted earth embankment, already as an integral part
of the body of the dam, for confining the aquifer in order to
permit the execution, during the rainy season, of grouting
at a higher elevation than the piezometric level of the aquifer
encountered;
• Execution of the grouting in the rainy season, and;
• Resumption of the earth embankment construction in
the following dry season.
The first perforations confirmed the impossibility of
performing the drilling by conventional methods. The
solution adopted was to mobilize high power drills which
permitted sinking large diameter metal linings.
The first grouting also confirmed the high complexity
of the anomaly encountered, with large takes of solids
without plugging, abrupt variations of the top of the bedrock,
instability of the drill-holes, decomposed materials
alternating with sound rock and the presence of a thick
layer of decomposed and erodible materials over the top
of the bedrock that presented karstic cavities.
In view of the difficulty encountered by the initially
adopted grouting procedures, the initial methodology was
adjusted by the creation of two external lines of grouting
to be first grouted with mortar of low penetration properties
and that would permit the subsequent grouting of a central
line with fine grouts of high penetration.
During the execution of these external lines, as a result
of the difficulties encountered and the high takes, it became
necessary to introduce a means of reinforcing them with
the execution of intermediate holes. After the conclusion
of the external "retaining" lines, the injection of the central
grouting line was commenced.
The grouting of the central line indicated that, despite
the high takes of solids in the external lines, the expected
improvement of the rock mass failed to occur as regards
the reduction in the consumption of solids and the
geomechanical characteristics of the rock, principally in
the locales containing decomposed and sandy materials
which, due to the grain size distribution presented, did not
permit the entry of the cement grout into the cavities. That
is, the grout takes of the central line were also high.
In order to permit following the construction schedule
of the dam embankments and faced by the need to
complement the treatment, it became necessary to
relocate the dam axis downstream of the area of
interference.
The displacement downstream of the axis of the dam
permitted introducing a berm over the region of the
treatment and concluding the embankments of the body
of the dam within the deadline scheduled for the
impoundment of the reservoir. The additional treatments
planned to be executed at the locale would be carried out
upon the surface of the berm and in parallel with the
298
construction of the earth embankments of the dam.
The quantities of the services corresponding to the
treatments performed were as follows:
• Holes grouted
214 units (holes with diameters
of 5" and 6")
• Length of drilled holes
10,600 m
• Solids injected
1,345.2 ton
• Average take of solids per metre
126.9 kg/m
The analysis of the treatment performed indicated that
although the grouting had been relatively efficient in the
treatment of the rock with the filling of the majority of the
cavities supposedly existing, in the region of the occurrence
of the decomposed materials the grouting failed to improve
the geomechanical characteristics of this material, because
the probability still existed of the occurrence of piping
processes within this material towards the cavities existing
downstream and which were not grouted due to their being
outside the radius of influence of the treatment. It was
therefore decided to introduce an impervious diaphragm
to intercept the karstic features along their entire extension.
Three alternatives were analysed regarding the
introduction of the impervious diaphragm by means of the
following processes:
a) Jet Grouting
b) High-power Hidrofesa drilling equipment
c) Overlapping Large Diameter Pilings (Secant piles cut
off)
Alternative "a" - Was eliminated due to the uncertainty
regarding the geomechanical quality improvements of the
rock mass with respect to erodibility resulting from the
alternative layers of decomposed and sound materials,
which did not permit extending the treatment to the zones
resulting from the sound materials.
Alternative "b" - Although technically more
recommendable, it was rejected due to the need for
importing special equipment of large size entailing a delay
exceeding the time limits of the construction schedule
and the date for the filling of the reservoir. The minimum
term for the mobilization and importation of the equipment
would be about six months, a delay totally incompatible
with the date for commencing the filling of the reservoir.
Alternative "c" - Was feasible from the technical and
schedule conformity viewpoints, considering that the survey
taken with the firms specialising in foundations indicated
the availability of WIRTH equipment in Brazil with the
possibility of mobilization within 30 to 60 days, reckoned
from the issue of the mobilization order. This term would
be required for equipment maintenance and the importation
of replacement parts. The equipment in question had
capacity to drill to the specified depths at a diameter of
1.80 m. See Figures 12 and 13.
Figure 12 shows the quantities involved in the execution
of the waterproof cut off by the secant piles process. The
pilings employed were 98, at an average depth of 53.5 m
(minimum 15 m and maximum 78.7 m).
In order to conform to the date for the impounding of
the reservoir, together with the execution of the treatments,
Main Brazilian Dams III
it was necessary to introduce a new alteration in the
conception of the project, consisting in the construction
of a cofferdam linked to the body of the dam, around the
area of the treatments, thus permitting the continuation of
the latter when the reservoir water levels reached the locale.
A platform in compacted earth embankment was built
at El. 258.00 m, in the interior of the dewatered area, and
which would prevent the welling up of water in the working
area after the impounding of the reservoir.
Technical Characteristics of the Wirth Drill
• Maximum drilling range
80 m
• Drilling diameters
0.80 m to 2.0 m
• Rotary head bit with 60 ton "pull down"
• Torque
3.5 to 12 t/m
• Maximum inclination - 1
3 (~18.5 degrees)
• Maximum drilling stroke
3.50 m
Figure 12 - Data of the Secant Piles Cut Off
299
Main Brazilian Dams III
Figure 13 - Operation of the Wirth Drill
7. PERFORMANCE OF THE
DEVELOPMENT
The monitoring instrumentation is installed at various
points of the Peixe Angical HPP, as briefly illustrated in
the Table 9.
One of the points judged as being priorities for
monitoring was the cofferdam at station 160, after the
flooding of the enclosure.
The observations resulting from the technical
inspections and the monitoring of the civil structures of
the Peixe Angical HPP indicated a normal behaviour when
submitted to the loads applied in the operational phase
in the period from April of 2006 to March of 2007.
The monitoring of the structures was performed by
measurements in the gallery of El. 233.50 m, in the set
of multiple extensometers and piezometers installed in
the foundation of blocks 2, 17, 20 and 28 and of the
piezometers installed in the foundation of blocks
5, 8, 11, 14, 23 and 26, in the triorthogonal jointmeters
installed between all the blocks, in the thermometers
installed in the concrete of the blocks 2, 5, 11, 17, 23
and 28, and in the measurement of the water coming
from the drains of the foundation rock.
Topographic targets were installed in all the blocks
on the crest of the dam in order to measure the
settlements.
The following behaviour was observed:
Concrete structures - the flows measured presented
tendencies towards stability or decrease and the values
measured conform to the limits established by the design.
Spillway and concrete dam - the effect of the elevation
of the reservoir level is reflected in the horizontal
Table 9 - Monitoring Instrumentation
300
Main Brazilian Dams III
displacements.
All the triorthogonal jointmeters installed in the central
wall, spillway, concrete dam and water intake indicated
only very small relative movement between the blocks.
Station 160 - Good performance of the piezometers
in the areas as shown in Figure 14.
Flows measured - the analysis of the flowmeter graphs
indicate that the values measured are more influenced
by the rainy periods than by the variations of the reservoir.
Earth dams on the right and left bank - behaviour within
the predictions of the design.
8. ENVIRONMENTAL, SOCIAL AND
ECONOMIC ASPECTS
The environmental impacts resulting from the
construction of the Peixe Angical Hydroelectric
Development were minimized by the implementation of
tywenty nine specific environmental programmes proposed
in the Environmental Impact Study - EIS, detailed in the
stages of the Basic Environmental Design - BED.
The mitigating, compensatory and the monitoring
measures were incorporated into the set of the twenty
nine Environmental Programmes integrating the BED,
and listed as follows:
• Monitoring of the Local Climate;
• Monitoring of Water Levels
• Monitoring of Sedimentation
• Monitoring of Seismic Activity
• Monitoring of the Shoreline Slopes
• Hydrogeological Monitoring
• Recomposition of Degraded Areas
• Research and Management of the Flora
• Deforestation and Cleanup of the Reservoir
• Monitoring and Management of the Fauna
• Limnological Monitoring
• Monitoring and Conservation of the Ichthyofauna
• Conservation Unit
• Reservoir Protection Belt
• Land Acquisition
• Recomposition of the Roadway Infrastructure
• Improvement of the Social Infrastructure
• Urban Relocation
• Rural Relocation
• Monitoring the Living Standards of the Population
• Recomposition of the Touring and Recreation Areas
• Public Health
• Rescue of the Archaeological Heritage
• Environmental Education
• Social Communication
• Mineral Sector
• Installations to Support the Construction
• Recomposition of the Social Services
• Record of the Historical Heritage
8.1. Measures Taken to Mitigate the Environmental
Impacts
1. Teams of professionals with proven experience in
hydroelectric developments;
2. All-encompassing Technical Specifications, with
objective technical parameters, specific methodology
and continuous monitoring of firms providing services;
3. Integrated Management of the Environmental
Programmes;
Figure 14 - Behaviour of the Piezometers at Station 160
301
Main Brazilian Dams III
4. Reports and continuous flow of information on the
implantation of the Environmental Programmes
presented to the Environmental Authorities;
5. Involvement of the communities in the implantation
of the Environmental Programmes;
6. Establishment of a good Geographical Information
System with a good resolution satellite image for
monitoring and full information;
7. Establishment of monitoring campaigns with
recognized technical parameters and the participation
of nationally renowned institutions, both for Health and
Vectors, Fauna, Flora, Water Ichthyofauna, Foci of
Erosion, Sediments, etc.
8. Strong Social Communication Programme
developed with the institutions and communities.
8.2. Measures Taken to Mitigate the Social Impacts
1. Institution of a Negotiation Forum with the participation
of Environmental Authorities, entities representing the
affected people, trade unions, city halls, etc., for the
discussion and accompaniment of the programmes of
Indemnities for Properties, Rural and Urban Relocation
and Municipal Infrastructure;
2. Social Agreement by Consensus and not by vote.
Lacking Consensus, the Arbitration is by the Federal
Justice;
3. Full participation of the communities in the definition
of the parameters and criteria for Relocation and
Resettlement, based on the Environmental Programmes;
4. Definition of the matching funds provided by the entities
for the implantation of the Programmes and Projects;
5. Wide ranging Programme of Technical and Social
Training and Qualification;
6. Full Technical Assistance - Agreement with state
institution and specific Plan prepared together with the
communities;
7. Wide ranging monitoring of the living standards of
those affected, with the contracting of the reference
institution (University/NGO) and accompaniment through
a Task Force formed by the Environmental Authorities,
representatives of those affected, City Halls.
8.3. Measures taken to mitigate the Economic
Impacts
1. Contacts with municipal and state institutions for the
convergence of projects and resources devoted to the
mitigation of the economic impacts, or better still, the
empowerment of the possibilities generated by the
development - Projects for Fruit Cultivation, Handicrafts,
Literacy Training, Sanitation, Environmental Education,
Tourism, Small Businesses, etc.
2. Agreement with institution specialized in the training
of manpower for the provision of professional training
courses considering the potentials and abilities of the
population of the municipal townships. Close to
150 courses were held in Peixe involving approximately
3,000 people.
302
3. Application of the resources of Support to the
Infrastructure of the Townships in accordance with the
structural necessities and not the desires of the municipal
mayor. Priority is to be granted to the areas of Health,
Education, Tourism and Recreation.
9. TECHNICAL FEATURES
General
Location River
State
Townships
Tocantins
Tocantins
Peixe and São Salvador do Tocantins
Period of Construction
Year commenced
Year concluded
April 2002
September 2006
Owner
Enerpeixe S.A, constituted by the firms:
Energia do Brasil S.A and Furnas Centrais Elétricas S.A.
Contractors
Designer THEMAG Engenharia e Gerenciamento S/C
Civil Contractors
Consórcio Construtor UHE
- PEIXE, formed by the firms:
Construtora Andrade Gutierrez S.A.
Construtora Norberto Odebrecht S.A.
Suppliers and Erection: CEPAN, formed by the firms:
VOITH SIEMENS Hydro Power Generation Ltda.
BARDELLA S.A. Indústrias Mecânicas
Basic Data
Drainage area of the dam
Mean annual precipitation
Mean annual temperature
Reservoir
Area at maximum normal level
Total storage volume
Active storage volume
Length
Maximum normal water level
Max. flood water level
Minimum water level
Tailrace channel
Max. normal water level
Max. flood water level
Minimum water level
Flows
Mean inflow
Max. flow recorded
Min. daily flow recorded
Diversion flood (Tr =50 years)
Max. design flood
125,687 km²
1,500 mm
25º C
294.10 km²
2,741 X 106 m³
528.3 X 106 m³
120 km
263.00 m
265.21 m
236.00 m
241.58 m
249.25 m
233.24 m
1,593 m³/s
11,256 m³/s
227 m³/s
14,550 m³/s
42,500 m³/s
Main Brazilian Dams III
Dam
Type of structure
Earth - Rockfill and RCC
Total length of crest
5,755.00 m
Maximum height
39.00 m
Crest elevation of earth & RCC dam
266.00 m
Rockfill
566,363 m³
Concrete (VCC - incl. Downstream)
27,870 m³
Compacted embankment
4,660,194 m³
Filters and transitions
768,393 m³
Concrete (Conventional - RCC)
317,456 m³
Spillway
Type
surface, with gates
Capacity
37,044 m³/s
Sill elevation
241.00 m
Total length
213.00 m
Number of bays
9
Width of bay
17.00 m
Common excavation
593,950 m³
Rock excavation (open sky)
429,848 m³
Concrete (Spillway only)
207,437 m³
Concrete (VCC - Spill. + Dissipation Pool) 270,068 m³
Spillway Gates
Type
Drive
Width
Height
Radial
Oil - Hydraulic
17.00 m
22.82 m
Water Intake
Type
Number of units
Total length
Width: blocks of the units
Water Intake Gates
Type
Drive
Width
Height
Diversion
Type
Diversion structure
gravity
3
30.00 m
98.10 m
Fixed Wheel
Oil - Hydraulic
6.80 m
16.60 m
Channel in riverbed
Channel and 1st and 2nd phase
cofferdams
Powerhouse
Type
Indoor
Number of generator units
3
Width of unit blocks
98.10 m
Total length
53.65 m
Common excavation: (includes headrace/tailrace
channels)
66,437 m³
Rock excavation (open sky including
channels)
571,185 m³
Concrete (VCC / Tailrace + Water Intake) 195,580 m³
Turbine
Type
Number of units
Unit rated power
Synchronous rotation
Net reference head
Rated unit flow
Maximum efficiency
Total weight per unit
KAPLAN
3
153.12 MW
85.71 rpm
24.30 m
688.00 m³/s
93.8 %
643.0 t
Generator
Rated power per unit
Synchronous rotation
Rated voltage
Maximum efficiency
Power factor
Total weight per unit
175 MVA
85.71 rpm
13.8 kV
98.70 %
0.95
834.2 t
Step-up Transformers
Rated power (OFAF)
Rated frequency (Hz)
Primary coil voltage
Secondary coil voltage
Winding connection
Primary connection
Secondary connection
delta
grounded star
Excavations
Common excavation
Rock excavation
6,464,459 m³
1,024,034 m³
175 MVA
60 Hz
13.8 kV
138 kV
10. BIBLIOGRAPHY
[1] ENERPEIXE - Progress Reports of Peixe Angical
HPP: from 2003 - 2006.
[2] ENERPEIXE - Themag Engenharia e
Gerenciamento S/C LTDA - Report 6376-10-GL-100-RT00190, Basic Project - Descriptive Spreadsheet;
[3] FURNAS CENTRAIS ELETRICAS - Departamento
de Apoio e Controle Técnico Relatório DCT.
T.08.015.2004-R0 - ENERPEIXE S.A.;
[4] FURNAS CENTRAIS ELETRICAS - Departamento
de Geração de Construção Manso Relatórios DGA.
C.018.2006-R1 - Peixe Angical HPP.
[5] ENERPEIXE - Relatório sintético do tratamento
da fundação da barragem de terra da margem esquerda.
(2006)
[6] THEMAG ENGENHARIA E GERENCIAMENTO
S/C LTDA - Relatório THEPEIXE080405 E-160 , 8.04.2005;
[7] FURNAS CENTRAIS ELETRICAS - Departamento
de Engenharia Civil Relatório DEC.E.025.2007-1 - Estudo
de Comportamento da Barragem AHE Peixe Angical.
[8] ENERPEIXE - Relatório PX- SP- 2000- RT-0063:
Tratamento da Fundação da Barragem de Terra da
margem esquerda UHE Peixe Angical. (21/03/2006).
303