BOTTOM DRAIN OF THE JAROSA DAM. MADRID (SPAIN)
The construction of a new bottom drain at The Jarosa Dam (Guadarrama, Madrid) was carried out in 2008 at the request of Canal de Isabel II in order to improve the operational safety of the dam and comply with the recommendations of current regulations. The execution of the work was carried out by Obras y Servicios Públicos S.A. (OSEPSA), subcontracting the excavation of the body of the dam by jacking pipe with closed shield tunnel boring machine AVN to the company Europea de Hincas Teledirigidas S.A.U - EUROHINCA.
WHAT?
Bottom drain of The Jarosa Dam.
WHO?
Client
Canal de Isabel II
Main Contractor
OSEPSA (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 Jarosa was in February 2008.
WHERE?
The Jarosa Dam, Guadarrama, Madrid, Spain.
Image 1: The Jarosa Dam location.
WHY?
The reservoir of The Jarosa, located in the municipality of Guadarrama (Madrid) was built in 1968. It consists of a straight-plan gravity dam, with 54 m of coronation height and 213 m of length, and supplies water for human consumption permanently to several municipalities in the Sierra Oeste of the Community of Madrid. In order to improve the operational safety of the dam and comply with the recommendations of current regulations, it was planned to execute a new bottom drain without emptying the reservoir, by jacking pipe using a closed shield tunnel boring machine.
The final objective of the new bottom drain was to allow the relief of water in case of failure of the existing one, as well as to reduce the emptying time of the reservoir in case of structural failure, in addition to allowing the correct regulation of flows.
There was also the condition that supplies to the municipalities had to be maintained during its construction, so it was not feasible to empty the reservoir.
Image 2: The Jarosa reservoir view.
Image 3: The Jarosa Dam view.
HOW?
The choice of the construction process depended on two constraints. One, the water supply to the municipalities had to be maintained and, therefore, the emptying of the reservoir was not viable. This required the use of a method that ensured tightness on the excavation front. On the other hand, the small diameter required according to the Project Instruction (800 mm interior), made it extremely difficult to manually excavate the dam.
Image 4: Work area.
Finally, the works consisted of a 31 m long drilling in the body of the dam, by jacking pipe of reinforced concrete pipes with an inner diameter of 800 mm and 1,110 mm outside executed with an AVN hydroshield type closed shield microtunneling machine. The beginning of the excavation was made downstream of the dam and its submerged exit to the reservoir upstream, where the machine was recovered.
Image 5: TBM entrance at the ground.
First, a launching shaft was executed for the support of the jacking frame, introduction of the TBM and the assembly of the pipe.
After the TBM, a watertight gate was installed on a section of steel pipe, which allowed, once the water was reached from the reservoir, to remove the TBM and continue working inside the pipe without the presence of water, to inject the back of the pipes and execute the anchors of the pipe to the body of the dam.
Once the reservoir was reached by the tunnel boring machine, it was lifted by divers to the crane located at the crest of the dam. Once the TBM was lifted, the thrust to the final position was completed and the watertight gate was closed.
Then, with the help of divers, the inside of the TBM was flooded from the reservoir to balance pressures. Once achieved, it was necessary to separate the TBM from the watertight gate in order to recovery it.
Image 6: TBM recovery.
Subsequently, the overcut was filled by mortar injections through injectors arranged radially for this purpose in the concrete pipes, which was able to eliminate the water from the back of the pipe and reduce the pressures of the body of the dam. After this, the work of anchoring the pipe to the concrete of the dam was carried out, to avoid the displacement downstream due to the push of the water on the watertight gate.
Finally, the jacking frame and the rest of the drilling equipment were removed, as well as the couplings and valves were assembled, in order to fill the interior of the pipe with water and connect to a hydraulic power plant located at the top.
Laura Céspedes y Marc Martí
TUNNEL TECHNICAL DATA
Length
31 m
Inner diameter
800 mm
Outter diameter
1100 mm
Slope
Horizontal drilling
Geology
Concrete (Dam structure)
TBM
Hydroshield AVN Herrenknecht
BIBLIOGRAPHY
ARTÍCULO-PRESA-LA-JAROSA.pdf (osepsa.es)
077-Proyecto de segundo desagüe de fondo de la presa de la Jarosa (Madrid) | OSEPSA
https://www.spancold.org/wp-content/uploads/2017/08/VIIIJEP_050.pdf
cced5495-6f14-6533-40b3-6ae259b9438d (canaldeisabelsegunda.es)