SEA OUTFALL FOR THE WWTP OF LAGARES, VIGO (SPAIN)
The project for the sea outfall execution of the WWTP of Lagares (Vigo) was tendered by ACUAES and awarded in 2013 to the UTE DRAGADOS, S.A. – DRACE INFRAESTRUCTURAS, S.A., subcontracting the construction of the onshore section and the offshore section through the technique of pipe jacking with closed shield tunnel boring machine AVN to the company Cimbras y Geotecnia, S.L. – MECANOTUBO.
WHAT?
Execution of the sections in pipe jacking technique of the sea outfall of the WWTP of Lagares, Vigo.
WHO?
Client
Aguas de las Cuencas de España
Microtunneling Contractor
UTE DRAGADOS-DRACE
Microtunneling Contractor
Cimbras y Geotécnia, S.L. (MECANOTUBO)
WHEN?
The construction of the sea outfall of Lagares (Vigo) began in 2014 and on February 15th of 2017 the operational tests of the new Wastewater Treatment Plant (WWTP) of Lagares (Vigo) began before starting the final commissioning phase in 2018.
WHERE?
Lagares, Vigo (Spain).
Image 1: Lagares Sea Outfall location.
WHY?
The execution of the sea outfall is part of the new Lagares Wastewater Treatment Plant (WWTP), which was designed to solve the serious deficiencies in the wastewater treatment that existed in the Vigo estuary. The solution developed to meet the water quality objectives in the Vigo estuary associated with the sanitation of the City Council of Vigo is made up of the following infrastructures:
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Expansion and modernization of the Lagares WWTP.
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Sea outfall of the Lagares WWTP.
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Extension of the existing electrical connection.
The following image shows the three main parts of the project:
Image 2: Project of the sea outfall of the WWTP of Lagares.
Once the three infrastructures are put into operation, Vigo's sanitation system would be completed, complying with the European Directive on wastewater treatment, especially regarding the microbiological quality necessary to meet the quality requirements of shellfish farming and bathing water.
The new WWTP was designed for a maximum treatment capacity of 800,000 equivalent inhabitants and the maximum flow of the sea outfall is 8 m3/s, which coincides with the maximum capacity that the collector network can currently incorporate into the WWTP.
Image 3: Aerial view of the new WWTP of Lagares.
Through the sea outfall, the effluent of the new WWTP is conducted from a loading chamber located in the treatment plant enclosure and equipped with a pumping system that comes into operation in a programmed manner according to the combination of flow values and tidal levels.
Image 4: Aerial view of Vigo estuary.
HOW?
The sea outfall consists of the following infrastructures:
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Loading chamber and pumping station.
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Emergency spillway.
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Casket of Samil.
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Onshore section of the sea outfall, executed in pipe jacking.
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First offshore section of the sea outfall, executed in pipe jacking.
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Second offshore section of the sea outfall, executed in trench.
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Diffuser section.
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Electrical installations.
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Control facilities.
The work area for the execution in driving was established in the parking lot of the beach of Samil, in a recito of about 3,500 m2 where the Samil casket is located, which was used as a launching shaft for the two sections executed in pipe jacking with a closed hydroshield tunnel boring machine AVN.
Image 5: Implantation of equipment in the Samil shaft.
Offshore section
The first phase was the execution of the offshore section with a length of 693 m with reinforced concrete pipes of 1,800 mm inner diameter and 300 mm thickness. The layout is straight and in elevation has a concave alignment of radius 3,815 meters. As for geology, in this section appears granite with an alteration grade III and granite residual soil (jabre), geology that impacts the drilling advance and the wear of the cutting wheel.
Image 6: TBM in the Samil shaft.
The guidance system used by the machine was the UNS system of Herrenknecht, using in the first 150 meters of the straight section without curved alignment the ELS mode and then the GNS mode consisting of a gyroscope (MWD II model) to determine the planimetric position of the TBM and a hydrostatic level to determine its elevation.
Image 7: ELS card and gyroscope (MWD II)
The execution of the section began on June 15th of 2015 with a duration of 3.5 months. After completing the tasks of dismantling and injection of cement grout, the bulkhead was installed in the last concrete pipe located in the launching shaft to flood the tunnel avoiding the flooding of the shaft itself.
Image 8: Bulkhead installed on the last pipe of the sea outfall.
The TBM recovery pit was located on a rock front about 19 meters deep under the sea. To recover the machine, a platform of approximately 20 meters was executed with a gravel bed for the support of the tunnel boring machine in its breakthrough.
Regarding the recovery, highlight the following activities:
· Complete dredging of the gravel filling the bottom of the pit leaving the TBM completely free of material.
· Pressurization of the TBM with a pressure of 2.0 bar.
· Connection to the TBM of a recovery beam to ensure that the pull is distributed equally, avoiding that the modules of the TBM can be separated.
· Installation of compressed air balloons for flotation and transfer of the TBM to the port.
· Hooking and lifting of the TBM in the port up to the surface to finish the recovery.
Following the driving section, the sea outfall continues with a high-density polyethylene (HDPE) pipe anchored on the seabed with an approximate length of 2,327 m, including the diffuser section, and 2,000 mm in outer diameter, which ends in a section formed by 62 diffuser intakes. The diffuser section, which has a length of 335 m, pours between 36 and 40 meters deep.
El perfil longitudinal del tramo submarino tiene una pendiente siempre descendente no inferior al 0,2 %, y sin puntos altos. En sus primeros metros se encuentra alojada en zanja excavada en roca y arena con proporciones variables en función del perfil geotécnico.
Para garantizar la estabilidad de la conducción instalada en el fondo, ha sido necesario lastrarla con anillos y yugos de hormigón para equilibrar los esfuerzos horizontales inducidos por la hidrodinámica de la zona.
The longitudinal profile of the submarine section has a slope always descending of not less than 0.2%, and without high points. In its first meters it is housed in a trench excavated in rock and sand with variable proportions depending on the geotechnical profile.
To guarantee the stability of the conduction installed at the bottom, it was necessary to ballast it with concrete rings and yokes to balance the horizontal forces induced by the hydrodynamics of the area.
Onshore section
In the second phase, the onshore section with a length of 780 meters was executed from the same launching shaft and with the same tunnel boring machine. This section connects the Samil casket with the pumping chamber located in the Lagares WWTP, crossing the Lagares River and Xunqueira do Lagares.
The layout in plan is straight and in section has a concave alignment of radius 2,411 meters, and the existing geology, paragneis with degree of alteration IV-V and granite with degree of alteration III are drilled.
Drilling began on November 20th of 2015 with a duration of 5 months until the recovery of the TBM in the recovery pit.
TUNNEL TECHNICAL DATA
Length
693 m
Inner diameter
1.800 mm
Outter diameter
2.400 mm
Slope
Initial descending to 1.6% and ends up descending to 0.3%
Geology
Granite grade alteration III and granite residual soil (jabre).
Starting Level
-6.10 m
Ending Level
-13.00 m
Working Pressures
Up to 2 bar
TBM
Hydroshield AVN (Herrenknecht)
Intermediate Jacking Stations
7
BIBLIOGRAPHY
PROIN3D: Emisario de Lagares (2013)
La tuneladora avanza ya bajo la orilla de Samil en el montaje del emisario para la depuradora
EDAR de Lagares: La mayor inversión que se está llevando a cabo en Vigo
EDAR de Lagares
Reparada la segunda rotura del emisario de la depurada del Lagares
La depuradora vierte al río Lagares el agua procesada tras averiarse el emisario submarino