Tag Archive: Aguapey


 

 

 

 

 

 

 

YACYRETA HYDROELECTRIC POWER PLANT

 

WORKS FOR THE PROTECTION OF THE AGUAPEY STREAM

 

Introduction

 

Aguapey Stream Basin Protection is one of the main works for the finishing of Yacyreta Reservoir Project. This Project is fundamental since its completion will impede the flooding of vast territories of the Republic of Paraguay thought the elevation of the reservoir storage level to its definitive height of 83 m above sea level.

Main works consist of 64.5 km of land dams which begin in the left margin of the river in Rincon de Santa Maria, cross over the main branch where they reach a maximum height of 43 m. After covering part of Yacyreta Island, cross over Aña Cua branch, then continue through the right margin 25 km, finishing in Paraguay’s San Cosme and Damian cities.

Nearby Damian city is Aguapey Stream, tributary of Parana River, which discharges an average flow of 25 m3 / s over the reservoir at a level of approximately 78 meters.

The Elevation of the Reservoir to its definite storage level of 83 masl would flood Aguapey Stream Valley, generating a sub reservoir of over 450 km2 of which 360 km2 correspond to mainland and wetland, and the remaining 200 km2 corresponding to productive land.

To prevent this situation, Protection Works of Aguapey Stream have been developed consisting of a land dam in the stream mouth to avoid flooding when the reservoir in filled with more than the current storage level and, a drainage channel of 12.5 km long downstream which connects with the collection channel that exists in the dam’s bottom until it reaches the Aña Cua branch.

 

Aguapey II – Aguapey Stream Closure Dam

 

The second stage of the work consisted in the construction of Aguapey Dam with an approximate length of 4.3 km. reaching to a crest elevation over the asphalt pavement of 86.45 masl, the construction of an irrigation channel in the Paraguayan margin and the Closure of the Temporary Deviation and the Opening of Aguapey Deviation Channel simultaneously.

The original Dam Project included in the bidding documents consisted on a body of soil and a blanket towards the reservoir. The Dam contained two lower clay cofferdams in the stream channel bed that along with the blanket were works performed over 14 years ago. All the leaking control in the foundation relied on the blanket and wells of relief.

The Work consisted on the drainage of the sector between both cofferdams and the continuation of the Dam building works until it reaches a final profile of 86.45 masl.

Before the construction started, work direction had begun, by conducting a geological-geotechnical auscultation of the stream channel, the cofferdams and the blanket, in order to reassure that the emptying of the precinct was done in a safety manner.

This study was meant to contemplate the current state of the work that was going to be part of the final project, and the fact that the reservoir level was higher than the level expected when the dam was planned.

As a result, the conclusion was that the bottom of the stream presented significant soil heterogeneity with important permeable sand layers and that the blanket had low waterproofing capacity.

After calculations of thin matter in which filtrations and slopes stability were analyzed, the conclusion was that the central precinct couldn’t be emptied without risking   siphoning effect and cofferdams failure. Even though it was possible to empty the precinct up to a level of 76.50 masl, the work between both cofferdams should be done under a strap of approximately 4 m of water.

Since the blanket provided a poor water proving capability, flow lines were to be prolonged underneath the dam so as to decrease the gradients to acceptable levels.

During design adjustment, 3 constructive alternatives were analyzed to enlarge the flow lines underneath the cofferdams precinct:

  • A bentonite screen constructed underneath the cofferdam in Yacyreta side that goes up to the waterproof mantles
  • A waterproofing of the bottom of the central precinct between the cofferdams through the placement of a concrete layer poured under water
  • The waterproofing of the mentioned precinct through the collocation of a waterproof membrane under water. 

Comparative Studies were done taking into account constructive complexities, costs, work safety and construction time since there were contractual key dates related to the expected time for the elevation on the storage level of Yacyreta Reservoir.

From those studies, the last alternative resulted as the most convenient being the new dam project as indicated in the diagram below:

With the alternative defined, the constructive challenge was the correct placement of the waterproof membrane under a strap of approximately 4 m of water.

Giving the critical conditions of the Project, after having the bottom waterproofed and before the drainage of the precinct, this one had to be filled up with sufficient weight so as to prevent a siphoning effect and stability mentioned before. Filling the area with sand coming from the Parana River was the most viable solution.

The selected membrane was made up of Polyvinyl chloride of 1.2 mm. thick and a resistance of 15 Mpa according to ASTM 882.

The membranes were rolled in rolls of about 1.80 m. The panels were welded by heat with controlled temperature to achieve complete fusion of juxtaposed panels, forming a single piece of the size of the precinct to be fulfilled.

The joints were tested in perpendicular tension to the seam making sure that they possessed greater strength than the membrane itself.

Before the placement of the waterproof membrane, another geotextile membrane was spread on the bottom to protect the former of any tearing element that may be deposited in the bed of the stream.

Alter being welled, the membrane was rolled and placed over a pontoon withheld and mobilized by a hoisting engine for a controlled placement of it over the bottom of the stream.

Before the filling of the precinct it was necessary to counterbalance the membrane to avoid dislocation or movements.

For this reason geocells of 7.5 cm high, 1.1 mm thick of geotextile were employed as well as concrete slipped in a working platform on a maximum area of 1500 cm2 to transform them into counterweight articulated sheets. Afterwards, they were lifted with a rocker arm and collocated over the membrane with a crane.

The positioning and the correct placement of the membrane as well as the geocells were inspected underwater by divers from the Consulting Consortium.

Once the membrane had been counterweighted, the hydraulic filling of sand took place up to the level of the new project.

Alter the filling was done, the precinct was drained to the expected levels continuing in this way with the work in the traditional way.

The new design is stable even though if the membrane deteriorates or even if it disappears during the work. Something that is highly improbable.

The Dam Project is completed with the construction of an irrigation channel on the Paraguayan side with a volume of 600m3 of reinforced concrete.

Special Tasks had to be made for the coordination of the closure of the stream discharge over the reservoir and the simultaneous opening of Aguapey Channel.

Those tasks were performed under strict supervision and having developed an Operative Plan and a Plan for Contingencies on the handling of the plug cofferdams and the Channel gates that provide all the possible contingencies and other exceptional events that could appear while the Aguapey sub reservoir drainage was done.

 

The main data of the project is the following:

 

The Project Adjustment, Inspection, Contract Administration and Work Direction were in charge of the Joint Venture COINTEC-INCONPAR-GCM-ELEPAR-GEIPEX-GCA UTE under the denomination ENERYA Consortium.

 

 

 

 

 

 

 

 

COMPLEJO HIDROELÉCTRICO YACYRETÁ

OBRAS DE PROTECCIÓN DE LA CUENCA DEL ARROYO AGUAPEY

 Introducción

La Protección de la cuenca del Arroyo Aguapey es una de las principales obras del Plan de Terminación de Yacyretá que es de fundamental importancia para la finalización del proyecto del Embalse de Yacyretá, en la medida en que su concreción impedirá el anegamiento de extensos territorios de la República del Paraguay ante el crecimiento de la cota del Embalse a su valor definitivo de 83msnm.

Las obras principales del aprovechamiento están compuestas por 64,5 km de presas de tierra que comienzan en la margen izquierda del río en Rincón de Santa María, cruzan el Brazo Principal donde tienen su mayor altura 43 m, luego de recorrer parte de la Isla Yacyretá cruzan el Brazo Aña Cuá, continuando luego por la margen derecha en una extensión de aproximadamente 25 km para finalizar en la ciudad paraguaya de San Cosme y Damián.

En las cercanías de esta última ciudad, se encuentra el Arroyo Aguapey, tributario del Paraná que descarga un caudal medio de 25 m3/s sobre el embalse a un nivel aproximado de 78 msnm.

La elevación del embalse a su cota definitiva de 83 msnm inundaría en contracorriente el valle del Arroyo Aguapey, generando un subembalse de más de 450 km2, de los cuales 360 km2 corresponden a tierras firmes y humedales y dentro de estas últimas 200 km2 se corresponden a tierras productivas.

Para evitar esta situación, se desarrollaron las obras de protección del Arroyo Aguapey consistente en una presa de tierra en la desembocadura del arroyo para evitar el anegamiento cuando se llene el embalse por sobre la cota actual de descarga y, aislado el arroyo y el embalse, un canal de 12,5 km de longitud que permita el escurrimiento del arroyo aguas abajo hasta conectar con el canal de colección existente a pie de presa hasta alcanzar el Brazo Aña Cuá.

Aguapey II – Presa de Cierre del Arroyo Aguapey

La segunda etapa de la obra consistió en la construcción de la Presa Aguapey con una longitud aproximada de 4,3 km, llegando hasta una cota de coronamiento sobre el pavimento asfáltico de 86,45msnm, la construcción de una Toma para Riego en la margen paraguaya y el Cierre del Desvío Temporario y la Habilitación del Canal de Desvío del citado Arroyo en forma simultánea.

El proyecto original de la presa incluido en los documentos licitatorios consistía en un cuerpo de suelos y un blanket hacia el Embalse Yacyretá. El cuerpo de la presa contenía dos ataguías inferiores de arcilla en el lecho del cauce del Arroyo que junto con el blanket eran obras realizadas hacía más de 14 años. Todo el control de filtraciones en la fundación estaba confiado al blanket y a los pozos de alivio.

La obra consistía en el vaciado del recinto central entre ambas ataguías y la continuación de las obras hasta completar el perfil final de la presa a nivel 86,45 msnm.

Durante la etapa previa a la construcción, comenzaron las tareas de dirección de las obras, realizando una auscultación geológica-geotécnica del cauce del arroyo, de las ataguías existentes y del blanket, a los efectos de asegurar que la orden de vaciado del recinto central pudiera realizarse con la seguridad adecuada para las obras, las personas y los equipos.

Este estudio debía contemplar el estado actual de las obras que iban a formar parte del proyecto final y el hecho que el nivel del Embalse de Yacyretá se había elevado respecto del considerado originalmente realizar para la construcción de la presa.

Como resultado del mismo, se llegó a la conclusión que el lecho del Arroyo presentaba una notable heterogeneidad de suelos con importantes estratos de arenas permeables y el blanket tenía una muy baja capacidad de impermeabilización.

Luego de un cálculo de elementos finitos mediante el cual se analizaron las filtraciones y la estabilidad de taludes, se llegó a la conclusión que el nivel del recinto central no podía vaciarse completamente sin un serio riesgo de sifonaje y fallas de los taludes de las ataguías. Si bien el recinto se podía vaciar hasta un nivel de 76,50 msnm, las obras entre ambas ataguías se deberían realizar bajo un tirante aproximado de 4 m de agua.

Dado que el blanket aportaba una reducida capacidad de impermeabilización, se debían prolongar las líneas de flujo por debajo de la presa a los efectos de bajar los gradientes a valores admisibles.

Durante la adecuación del diseño, se analizaron 3 alternativas constructivas para alargar las líneas de filtración por debajo del recinto entre ataguías. Una pantalla bentonítica construida por debajo de la ataguía del lado Yacyretá hasta alcanzar los mantos impermeables, una impermeabilización del fondo del recinto central entre las dos ataguías existentes mediante la colocación de una capa de hormigón colado bajo agua y la impermeabilización del recinto mencionado por la colocación de una membrana impermeable bajo agua.

Se realizaron estudios comparativos teniendo en cuenta las complejidades constructivas, los costos, la seguridad de las obras y los tiempos de construcción ya que existían fechas clave contractuales relacionadas a los tiempos previstos de elevación de la cota del Embalse de Yacyretá.

De estos estudios surgió la última alternativa como la más conveniente, resultando el nuevo proyecto de la presa con el esquema de diseño que se indica:

Definida la alternativa, el desafío constructivo era la correcta colocación de la membrana impermeable bajo un tirante aproximado de 4 m de agua.

Dadas las condiciones críticas del proyecto, luego de impermeabilizado el fondo y antes del vaciado del recinto, se debía proceder a rellenar dicho recinto con el suficiente peso para evitar los efectos de sifonaje y estabilidad antes mencionados. La solución más viable fue rellenar con arena refulada proveniente del Río Paraná.

La membrana seleccionada fue de policloruro de vinilo de 1,2 mm de espesor y una resistencia de 15 Mpa según ASTM 882.

Las membranas eran laminadas en rollos de alrededor de 1,80 m. Los paños fueron soldados por calor con temperatura controlada hasta lograr la fusión total de los paños yuxtapuestos, conformando así una única pieza del ancho del recinto a cubrir.

Las uniones fueron testeadas a tracción perpendicular a la costura verificando que las mismas poseían mayor resistencia que la correspondiente a la propia membrana.

Antes de la colocación de la membrana impermeable, se extendió sobre el fondo otra membrana de geotextil cuya única función fue proteger a la membrana impermeable de cualquier desgarro por eventuales elementos cortantes o desgarrantes que pudieran estar depositados en el lecho del Arroyo.

Luego de soldada la membrana fue enrollada en carretes del ancho requerido los cuales fueron dispuestos sobre un pontón retenido y movilizado por guinches, que permitió la extensión controlada de la membrana sobre el fondo.

Antes de proceder a la ejecución del relleno del recinto era necesario contrapesar la membrana para evitar efectos de descolocaciones o corrimientos durante el refulado.

A tal efecto se emplearon geoceldas de 7,5 cm de altura, 1,1 mm de espesor de geotextil y un área máxima de 1500 cm2 las cuales se colaron con hormigón en obrador para transformarlas en placas articuladas de contrapeso que fueron trasladadas, izadas con un sistema de balancín y colocadas con grúa sobre la membrana.

El posicionamiento y la correcta colocación de la membrana y de las geoceldas fueron inspeccionadas en forma subacuática por buzos del Consorcio Consultor.

Una vez contrapesada la membrana impermeable se comenzó con las tareas de refulado de arenas hasta los niveles del nuevo proyecto.

Completado el refulado se realizó el drenaje del recinto con los niveles de seguridad previstos continuando las obras en seco de forma tradicional.

Es de hacer notar que el nuevo diseño se comporta establemente, aún cuando la membrana se deteriore o incluso desaparezca durante la vida útil de la obra, cosa sumamente improbable.

El proyecto de presa se completa con la construcción de una toma de riego en la margen paraguaya con un volumen de 600 m3 de hormigón armado.

Debieron también realizarse especiales tareas de coordinación para el cierre de la descarga del Arroyo sobre el Embalse y la habilitación simultánea del Canal Aguapey.

Estas tareas se realizaron bajo absoluta supervisión y habiendo desarrollado un Plan Operativo y de Contingencias del manejo de las ataguías tapón y de las compuertas del Canal que contemplaran todas las posibles contingencias de crecidas y otros eventos excepcionales que pudieran presentarse mientras se realizaba el vaciado del Subembalse Aguapey.

Los datos significativos del proyecto son los siguientes:

La Adecuación del Proyecto, la Inspección, la Administración del Contrato y la Dirección de Obra estuvieron a cargo de la unión transitoria de empresas COINTEC-INCONPAR-GCM-ELEPAR-GEIPEX-GCA UTE bajo la denominación de Consorcio ENERYA.

 

 

 

 

 

 

 

 

YACYRETA HYDROELECTRIC POWER PLANT

WORKS FOR THE PROTECCION OF THE AGUAPEY STREAM

Introduction

 

The Protection of the Aguapey Stream Basin is one of the main works for the finishing of Yacyreta Reservoir Project. This Project is fundamental since its completion will impede the flooding of vast territories of the Republic of Paraguay thought the elevation of the reservoir storage level to its definitive height of 83 m above sea level.

Main works consist of 64.5 km of land dams which begin in the left margin of the river in Rincon de Santa Maria, cross over the main branch where they reach a maximum height of 43 m. After covering part of Yacyreta Island, cross over Aña Cua branch, then continue through the right margin 25 km, finishing in Paraguay’s San Cosme and Damian cities.

Nearby Damian city is Aguapey Stream, tributary of Parana River, which discharges an average flow of 25 m3 / s over the reservoir at a level of approximately 78 meters.

The Elevation of the Reservoir to its definite storage level of 83 masl would flood Aguapey Stream Valley, generating a sub reservoir of over 450 km2 of which 360 km2 correspond to mainland and wetland, and the remaining 200 km2 corresponding to productive land.

To prevent this situation, Protection Works of Aguapey Stream have been developed consisting of a land dam in the stream mouth to avoid flooding when the reservoir in filled with more than the current storage level and, a drainage channel of 12.5 km long downstream which connects with the collection channel that exists in the dam’s bottom until it reaches the Aña Cua branch.

In this article I will refer to Aguapey I – Aguapey Stream Discharge Channel

 

Aguapey I – Aguapey Stream Discharge Channel

 

The first stage of the construction consisted on a linking channel from Aguapey stream intake position to the station 12+500 in which a junction is made between this one and the channel at the bottom of the dam in order to derive water from the stream to the discharge area in the Aña Cua branch. Construction began in the second part of the year 2005.

The path of the trace was carried out mostly on clay soils, having to go through an important basalt mantle, sandstones and altered rocks between the stations 8+100 and 10+275.

The first excavations in these progressives allowed us to perceive the bedding state of rocky mantles, having as a consequence important alterations that required a demanding and heterogeneous slopes project to meet the safety of all personnel and equipment employed during the process of excavation and also to meet the channel’s medium and long term stability.

For this reason the degree of alteration, the jointing and the RQD of the rock mantle have been entirely analyzed and different sections have been designed to assure proper slope stability.

Due to the alteration of the rock mass, blasting methods were adjusted as regards positioning, separation, depth and drilling load to the effects of making blasting works more efficient.

Taking into account the deep alteration state of the rocks and sandstones present and giving prestige to the integrity of the work in its expected long lifetime, slopes that don’t require injected anchors as a means of support were decided.

 In some cases of deep alteration shotcrete protective paving was done.

Pure soil areas were found with a few little rock outcrops up to the station 8+000.

In almost every section clay soil was found and slopes and lines sections 3H: 1V were design.

In these sections, excavations were done with conventional high performance equipment through traditional methods and intensive dedication.

Slopes protection was done with medium rank rocks up to the berm, which is likely to get into contact with the water flow, and through a vegetable protection and stabilization drainages in superior areas that presented possibility of collapse.

Main data as regards dimensions:

Channel Length: 12.5 km.
Design Flood:   700 m3/ sec
Regular Excavation Volume: 8.640.079 m3
Rock Excavation Volume: 1.863.895 m3
Total Volume of the Excavation: 10.504.000 m3
Channel Maximum Depth:        39.0 m.
Channel Minimum Depth: 8.0 m.
Storage level of the Channel’s Sill: 69.00 masl.

 

The Channel is crossed by many different building works that completed the Project.

One of them is the crossing of the 5B Route in the station 9+400. This route had to be relocated and re-projected and its crossing required a viaduct to bridge the irregularities caused by the channel’s slopes. In the Interjection between the route and the channel a structure was built to control the flow of water.

The viaduct was design with premolded concrete beams that were mounted through the use of launching beams. The total concrete volume was 750 m3.

The central section contains the Channel’s Flow Control Structure, made of four big columns that hold three flat gates set on by hydraulic mechanisms.

These Gates will allow the realization of maintenance procedures downstream.

The Control Structure involved the realization of 2.230 m3 of concrete.

The Channel Crossings are completed by 3 bridges for animal transit and an irrigation bridge with a capacity of 108 m3 to irrigate arable land in Paraguay’s territory.

Aguapey Channel’s Works were successfully completed and in the original deadlines established in December 2007, except for the Irrigation Bridge. Its construction is to be decided by Yacyreta Binational Entity in a near future.

The Final Project, the Inspection, Contract Administration and the Building Work Direction were in charge of the Joint Venture COINTEC-INCONPAR-GCM-ELEPAR-GEIPEX-GCA UTE under the name of ENERYA Consortium.

COINTEC, from The Argentinean Engineering Consultants Chamber (Cámara Argentina de Consultores de Ingeniería) acted as the Argentinean leading company.