SEA OUTFALL FOR LAGARES WASTEWATER TREATMENT PLANT. VIGO (SPAIN)
In mid-2016, the Federal Electricity Commission (FEC) announced that Infraestructura Marina del Golfo (IMG) was awarded the construction and operation of the South of Texas – Tuxpan gas pipeline to meet Mexico's growing energy demand.
This pipeline has a transport capacity of 2,600 million cubic feet per day (approx. 74 million m3) and runs from the border with the United States near Brownsville, Texas to Tuxpan, in the state of Veracruz (Mexico).
The execution of the land-sea connection was carried out by pipe jacking method using reinforced concrete pipes with an internal diameter of 2,600 mm and AVN closed shield tunnel boring machine. This sea outfall would serve to house the gas pipeline (product pipe) formed by two twin 42-inch pipes, one inlet and one outlet, as it passes through the Altamira compression station.
The submarine pipeline, considered one of the longest executed by pipe jacking, has a total length of 2,246 meters.
The execution of this pipeline, carried out by Europea de Hincas Telemando S.A.U – Eurohinca, began in November 2017 completing the excavation work at the end of July 2018.
WHAT?
Land-sea pipeline for the installation of the South of Texas – Tuxpan gas pipeline as it passes through the Altamira compression station (Mexico).
WHO?
Client
Comisión Federal de Electricidad (CFE)
Microtunneling Contractor
UTE DRAGADOS-DRACE
Microtunneling Contractor
Cimbras y Geotécnia, S.L. (MECANOTUBO)
WHEN?
The excavation works began in mid-November 2017 and was concluded at the end of July 2018 reaching the final position of the tunnel after excavating 2,246 meters. The installation of the gas pipeline as it passes through Altamira was successfully completed at the beginning of January 2019.
WHERE?
Lagares, Vigo, España.
Image 1: South of Texas – Tuxpan Pipeline location
WHY?
The South of Texas – Tuxpan gas pipeline was built to meet Mexico's energy demand by transporting natural gas from South Texas to generation plants in Tamaulipas and Veracruz and other vital areas of the country as established by its National Development Plan (NDP).
The land-sea submarine pipeline executed by pipe jacking was the most critical and complex crossing of the project.
Image 2: Aerial view of work platform, salt flats and mangroves.
Una vez puestas en marcha las tres infraestructuras se completaría el sistema de saneamiento de Vigo dando cumplimiento a la Directiva Europea sobre saneamiento de aguas residuales, en especial, en lo referente a la calidad microbiológica necesaria para cumplir con los requisitos de calidad de la cría de moluscos y las aguas de baño.
La nueva EDAR fue proyectada para una capacidad máxima de tratamiento de 800.000 habitantes equivalentes y el caudal máximo del emisario es de 8 m3/s, que coincide con la capacidad máxima que puede incorporar en la actualidad la red de colectores a la EDAR.
Imagen 3: Vista aérea de la nueva EDAR de Lagares donde se conecta el emisario submarino.
A través del emisario submarino se conduce el efluente de la nueva EDAR desde una cámara de carga situada en el recinto de depuradora y dotada de un sistema de bombeo que entra en funcionamiento de un modo programado según la combinación de valores del caudal y las cotas de marea.
Imagen 4: Vista aérea de la ría de Vigo.
HOW?
For the execution of the land-sea connection of the gas pipeline, conventional execution methods were discarded due to high environmental restrictions, mangrove protected area, several surface water bodies and the existence of a coral barrier near the coast, finally opting for pipe driving as the most appropriate method to cover the 2,246 meters of underground crossing, turning the Altamira sea outfall into the longest sea outfall with direct exit to the sea in the world executed to date.
In order to execute the land-sea connection of the gas pipeline as it passes through Altamira, a work platform of more than 500 meters long and more than 100 meters wide was built. On the platform was built the launching shaft, executed by means of a screen wall or Milan wall with metal braces and distribution beams on three levels and the launch ramp necessary for the installation of the product pipe once the excavation and recovery works of the seabed tunnel boring machine have been completed.
The launching shaft had the particularity of being a rectangular shaft of 23.5 meters long between inner faces of the screens and 12 meters wide to be able to install a double jacking system to optimize the execution of the excavation allowing the simultaneous installation of up to three reinforced concrete pipes. The height of the bottom slab was located at a depth of about 12 meters from the upper level of the work platform.
Image 4: Launching shaft with bracing arrangement and distribution beam.
For the execution of the sea outfall, a tunnel boring machine (TBM) type AVN hydroshield from Herrenknecht was used. Given the characteristics and length of the drive, an additional module, called Push-Module, was designed and manufactured, which would allow the change of the installation mode of the tunnel lining, from pipe jacking to installation of segments rings if necessary, either by exceeding the pushing capacity or by not being able to advance with the excavation by jacking pipe.
Image 5: AVN hydroshield tunnel boring machine with OD3200 and emergency push module.
The layout in section of the projected microtunnel combined straight sections with two curved alignments, a first of 40,000 meters of radius and a second of 10,000 meters of radius, with entrance and exit slopes -2% and +2% respectively, being the layout straight in plan.
It is interesting to note the importance of the synergy between the execution of the tunnel and the subsequent installation of the pipeline to define the projected route.
Image 6: Longitudinal section of the microtunnel.
For the lining of the tunnel, reinforced concrete pipe was used with an inner and outer diameter of 2,600 mm and 3,200 mm respectively, with the length of each pipe being 2.84 meters. This pipeline would serve to house the gas pipeline (product pipe), formed by two twin lines of 42 inches (one of entry and one of exit as it passes through the Altamira compression station) and an additional lower line of 24 inches (approx. 610 mm) that would serve to perform the hydrostatic test and in case of future need, expand the capacity of the pipeline.
Image 7: Installation assembly of the product pipe (gas pipeline) inside the microtunnel.
A total of 752 pipes and 21 intermediate stations were jacked whose length, once closed, was 4.41 meters.
The first 10 pipes had a special design that allowed the sewing between them by means of screwed connections and joints with bolts to avoid the relative rotation between them, the purpose was to ensure that the first 30 meters behaved as a single pipe minimizing a possible risk of disconnection or differential settlement during the recovery and flood phase.
One of the challenges of the project was the choice of the guidance system not only for the final length to be executed but also for the characteristics of the push module (Push Module) installed behind the TBM. The lack of space and visibility between the ELS (Electronic Laser System) card installed in the first shield of the machine and the intermediate station-prisms assembly to be installed in the tunnel caused the alternative of using the SLS-LT system to finally use the GNS-HWL system to be ruled out, combination of a gyroscope to calculate the horizontal position and a water level to calculate the vertical position of the TBM.
The selected guidance system worked correctly and did not condition the progress of the excavation despite not having previous references for lengths greater than 2,000 meters.
During the excavation phase, different challenges were faced, one of them was the progressive lifting (known in English as upheaval) of the tunnel in the first 200 m where a layer of great power of very plastic clays predominated.
The maximum elevation recorded was close to exceeding 600 mm at some points as shown below.
TUNNEL TECHNICAL DATA
Length
693 m
Inner diameter
1.800 mm
Outter diameter
2.400 mm
Slope
Descending 2% at the input and ascending from 2% at the exit
Geology
High plasticity clays, silts, organic material and sands
Starting Level
-8.5 m (awl)
Ending Level
-11.5 m (awl)
Working Pressures
Hasta 2 bar
TBM
Hydroshield AVN (Herrenknecht)
Intermediate Jacking Stations
7
BIBLIOGRAPHY
Sea outfall executed by jacking pipe for the location of gas pipeline (Altamira, Mexico). Journal of Public Works (ROP 3624), October 2020.
https://www.tcenergia.com/activos/sistema-sur-de-texas-tuxpan/
https://trenchlesstechnology.com/2020-project-of-the-year-new-installation-runner-up/
https://www.napipelines.com/building-big-microtunneling-terratest-world-record-project/