BOTTOM DRAIN OF THE OLIANA DAM. LÉRIDA (SPAIN)
The construction of a new bottom drain in the Oliana dam (Lérida), was made in 2009, at the request of the Ebro Hydrographic Confederation, to solve exploitation problems caused by accumulation of sludge and saturation of sediments at the bottom of the dam, while guaranteeing a minimum flow of relief to the course of the river or ecological flow. The project execution was developed by Obras y Servicios Públicos S.A. (OSEPSA). The drilling works by means of an AVN hydroshield tunnel boring machine and the jacking pipe was executed by the company Eurohinca.
WHAT?
Bottom drain of the Oliana Dam.
WHO?
Client
Ebro Hydrographic Confederation
Main Contractor
Obras y Servicios Públicos S.A.
Microtunneling Contractor
Eurohinca (Europea de hincas teledirigidas S.A.U.)
WHEN?
The construction of the bottom drain of the Oliana Dam was executed during 2009. The starting works of drilling began on June 10th, 2009.
WHERE?
Oliana Dam, Lérida, Spain.
Image 1: Oliana dam location.
WHY?
The Oliana Dam stores water from the Segre River. Due to the accumulation of sludge and saturation of sediments, problems were occurring in its exploitation, so the Ebro Hydrographic Confederation decided to carry out an emergency work for the installation of an intermediate intake or mid-bottom drain. Within the same emergency work, the remodeling of the spillways of the dam was made with the installation of a new hydraulic system for the operation of the two existing gates.
This new intake, in case of failure of other elements, would guarantee the relief of the dam and/or the contribution of environmental flows to the Segre River and the flows granted to the fish farm located downstream of the reservoir. It also included the repair of the dam's spillways. It would also be a direct benefit for the surrounding localities as it is the starting point for the pipelines planned in the irrigation transformation projects of the municipalities of Peramola, Basella and Oliana.
Image 2: Dwonstream view of the Oliana dam.
HOW?
The construction of the new mid-bottom drain of the Oliana dam consisted of a drilling of 17.20 m in length in the body of the dam, by means of the technique of driving concrete pipe with sheet metal jacket of inner diameter 1,000 mm and 1,260 mm outter executed with a closed shield microtunnel boring machine type hydroshield AVN.
It should be noted that drilling began at 491 meters above water level (mawl in advance) with a horizontal slope, reaching a depth of 27 m with a pressure of 2.7 bar since the level of water upstream at the time of drilling was at 518 mawl.
For the preparation of the work platform it was necessary to demolish one of the concrete stair of 4.00 x 4.80 m of the wall downstream of the dam. Subsequently, the thrust wall had to be built to withstand the whole jacking force of the microtunnel. It was designed to resist a thrust of up to 200 t/m².
Image 3: Concrete stair demolition to create the work platform.
The AVN closed hydroshield used for the excavation was provided with a recovery module plus a lock that ensured the tightness of the pipe inside during the recovery of the TBM inside the dam. This recovery-lock module also served as a sealing of the pipe installed in the face of the dam until the downstream placement of the bottom drain shut-off valve. Once the bottom drain shut-off valve was installed, the recovery-lock module and the pipe were disconnected by means of self-propelled hydraulic cylinders that separated both elements and thus left the bottom drain operational.
The desander or separation plant was in an existing esplanade on the right abutment of the dam with easy access. The control equipment was on a structure created taking advantage of the stairs of the downstream facing, with direct view of the work area.
For the control of the TBM guidance, a laser guidance system was used, consisting of a laser emitter and a receiver or target installed in the TBM. The guidance system instantly monitored the TBM situation in the control cabin, showing the small deviations that were produced by the difference in the quality of the perforated concrete allowing the TBM operator to drive on the orientation cylinders to follow the exact axis of the perforation.
Image 4: TBM lifting to position it on working area.
Image 5: Working area viewed from dam crest.
Image 6: Thrust wall, jacking frame, TBM and control cabin.
To prevent water leakages from the dam during the TBM exit and along the tunnel through the through the overcut area, a watertight entrance joint with double sealing gasket was installed on the jacking frame.
Image 7: Concrete pipe introduction into the dam.
Once the drilling was completed, the overcut was filled (with an average thickness of 17.5mm) with aqua reactive resins. These injections were made through injectors arranged radially for this purpose in the concrete pipes.
Subsequently, the work of anchoring the pipe began, using the injectors (holes) of the concrete pipe through which the filling of the overcut had been made, to drill the back of the drain. 18 anchors were placed and joined to the concrete using high adhesion epoxy resin.
Finally, the jacking frame and the rest of the equipment was dismantled and to complete the project it only remained the installation of a closing element of the pipeline, the gate valve (Bureau type). This gate, with a diameter of 1,000 mm, ensured the tightness of the pipeline and allowed the installation of the stainless-steel pipe to the dam toe. The recovery module was removed, and the bottom drain of the Oliana dam was commissioned.
Laura Céspedes y Marc Martí
TUNNEL TECHNICAL DATA
Length
17,20 m
Inner diameter
1.000 mm
Outter diameter
1.260 mm
Slope
Horizontal drilling
Geology
Concrete (dam structure)
Starting Level
Up to 2.7 bars
Starting Level
Hydroshield AVN
BIBLIOGRAPHY
093 - Obras de emergencia para la instalación de una toma intermedia en la presa de Oliana | OSEPSA
Microsoft Word - OLIANA_JIA_11_01.docx (upm.es)
Microsoft Word - OLIANA V07.docx (osepsa.es)
Microsoft Word - n090401 Toma Oliana.doc (mpt.gob.es)
El Gobierno central adjudica la instalación de la nueva toma intermedia en la presa de Oliana (europapress.es)