SOREK II DESALINATION PLANT. PALMAHIM (ISRAEL)
In mid-2020, IDE Technologies was awarded the construction of a new desalination plant, Sorek B, located in Palmahim (Israel) with an annual treatment capacity of 200 million cubic meters. This plant, whose water treatment is carried out by reverse osmosis, is considered the largest in Israel and one of the largest of its kind in the world.
As part of its construction, three sea outfalls, two for feed or water catchment and an outfall for brine discharge were executed.
The execution of the sea outfalls was carried out by reinforced concrete pipes with an internal diameter of 2,600 mm with AVN closed shield tunnel boring machine.
The executed sea outfall for brine discharge is among the longest of its kind in the world and has a total length of 2,023 meters and the catchment inlets have an approximate length of 1,300 meters each.
The works were executed by the consortium Ofek – Eurohinca Sorek 2 Limited Partnership, starting the excavation works in mid-July 2021 and completing them in mid-November 2022, executing a total of 4,646 meters.
WHAT?
Two inlets for water catchment and an outfall for brine discharge from the desalination plant, Sorek B, located in Palmahim (Israel).
The executed submarine pipelines correspond to the submarine sections of the catchment and discharge pipes of the desalination plant, each pipeline consists of two other land sections.
WHO?
Client
The State of Israel/Water Desalination Administration (WDA)
Microtunneling Contractor
Sorek Desalination Facility 2 Limited Partnership (SDF2LP)
Microtunneling Contractor
Ofek Atarim and Eurohinca Tunneling
WHEN?
The three sea outfalls were executed between mid-July 2021 and mid-November 2022.
The desalination plant is scheduled to start operating in mid-2023
WHERE?
Image 1: Sorek II Desalination Plant location.
WHY?
The three subsea pipelines were designed as part of the new Sorek II desalination plant, as an extension of the existing plant, to increase the drinking water treatment capacity in Israel and meet the country's growing demand.
The desalination plant, which is treated by reverse osmosis, is considered the largest treatment plant in Israel and one of the largest of its kind in the world, with an annual treatment capacity of 200 million m3.
Image 2: Orthophoto of the feeds and brine lines
HOW?
For the execution of the desalination plant pipelines, two inlets for water catchment (FEED 1 and FEED 2) and a sea outfall (BRINE), the execution was chosen by trenchless technology, being the pipe jacking the method finally selected due to the high environmental restrictions of the area, since the terrestrial sections ran mostly within a protected national park and in the vicinity of a military base.
Each conduction consisted of three sections, two terrestrial and one maritime, the latter being the subject of the article.
Image 3: Scheme of the pipelines (FEED 1, FEED 2 and BRINE) to be executed by pipe jacking.
For the project completion, a work platform of approximately 10,000 m2 was executed in which the launching shafts were executed, two circular shafts of 15 meters in diameter and 12 meters deep for the execution of each inlet and another rectangular shaft of 22 meters long by 9 meters wide and a depth of 11 meters to house a double jacking frame for the execution of the sea outfall (BRINE). All shafts were executed by diaphragm wall with steel bracing in coronation in the case of the rectangular shaft.
Image 4: Aerial photograph of the work platform and launching shafts (February 2021).
A tunnel boring machine (TBM) type AVN hydroshield of Herrenknecht was used, after which a recovery module was installed to allow, on the one hand, to recovery the TBM to execute the next section and on the other, to guarantee the tightness of the tunnel to continue the works inside and the connection in the shaft between the submarine and the terrestrial section of each pipeline.
Image 5: Diagram of the TBM and the recovery module used for the execution of the submarine sections.
The pipelines layouts, both for the FEED 1 and FEED 2 and for the BRINE combined two straight sections at the ends with one curved in the center. In the case of the inlets, the projected curve was 50,000 meters in radius with entry and exit slopes of -1.2% and 0% (horizontal) respectively, while, in the case of the sea outfall, the central curve had a radius of 100,000 meters with entry and exit slopes of -1.5% and 0% (horizontal) respectively.
The geology found in each of the submarine stretches was mainly sands and clay and silty sands with intercalations of Kurkar (sandstone rock typical of the coast of Israel).
In the lining of the tunnel, reinforced concrete pipes was used with an inner and outer diameter of 2,600 mm and 3,200 mm respectively, being the length of each pipe 4 meters.
The first 10 pipes had a special design that allowed the union 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 meters behaved as a single pipe minimizing a possible risk of disconnection or differential settlement during the recovery and flood phase.
As an additional measure, the pipe of each submarine section behind the recovery module was ballasted to avoid possible buoyancy problems in the first meters of the tunnel during the recovery phase or connection of the intake towers, in the case of the inlets, or the diffuser, in the case of the outfall. In the outfall (BRINE) a metal lining was installed inside the first three pipes and in the case of the inlets (FEED 1 and FEED 2) the pipe in that section was partially flooded to reach an additional 1.5 tons per meter.
The last 5 pipes of each line were also special to facilitate the tying of the pipes together and the last of them was equipped with a special flange on its back to allow the connection of the reinforced concrete pipe with the connection section (spool piece) of the shaft, GRP pipe (Glass Reinforced Plastic).
Image 6: Last section reinforced concrete pipe with rear metal flange.
All the pipes had two types of gaskets, a primary type of Harpoon or Delta type by its shape and another secondary type Block to guarantee the tightness of the conduction.
At least one of every three pipes installed had three non-return valves, spaced 120 degrees apart, for the injection of bentonite into the back of the pipe during the execution of the excavation (lubrication system).
As a guidance system, the GNS-HWL system was selected, combining a gyroscope to calculate the horizontal position and a water level to calculate the vertical position of the TBM.
Image 7: GNS-HWL guidance system used in the execution of submarine tunnels.
One of the highlights in the execution of the submarine sections was their rapid execution and the thrust forces with which each of the sections was completed.
The best yields were recorded during the execution of the outfall (BRINE) despite being the most complex driving given its length, excavating a total of 2,023 meters. During its construction, the best yields of the project were obtained, with the best daily performance being 81 meters, possibly the best performance recorded worldwide in pipe jacking for that diameter, weekly performance of 300 meters and a monthly yield of 1,020 meters, all of them registered in the month of May 2022.
The 2,023 meters were executed in just 85 days, finishing its execution without using any of the 17 intermediate stations installed and with a thrust force from the jacking frame less than 900 tons as can be seen in the following graph, thrust forces lower than those initially planned during the study phase.
Image 8: Thrust forces vs. executed tunnel length (BRINE).
The execution of each of the submarine pipelines was completed with the recovery of the TBM once the excavation phase was completed and the closure of the intermediate stations installed, leaving the recovery module as a closure of the pipeline until the subsequent flooding of each of the pipes once all the land connections were made.
The recovery of the TBM was carried out up to three times after flooding the space between bodies (TBM and recovery module) and actuating the four front cylinders housed in the recovery module. Previously, the TBM had been pressurized between 2 and 2.5 bar to equalize the height of the water column at the point of arrival of each section and thus prevent water from entering the TBM.
The transport of the TBM from the recovery point to port was carried out with the TBM braced to the same vessel used for the recovery of the TBM and with it fully submerged near the surface of the water to take advantage of the vertical thrust force and reduce the weight of this as shown below.
Image 9: Representation of the fully submerged TBM braced to the rescue vessel.
Image 10: Tunnel boring machine in port after lifting by mobile crane.
Héctor Trigal
TUNNEL TECHNICAL DATA
Length
2 x 1,300 m (feeds) y 1 x 2,023 m (brine)
Inner diameter
2.600 mm
Outter diameter
3.200 mm
Slope
FEED 1 y FEED 2:
Descending 1.2% at the entrance and horizontal (0%) at the exit of the curve.
BRINE:
Descending 1.5% at the entrance and horizontal (0%) at the exit of the curve
Geology
Sands, clay/silty sands and Kurkar intercalations.
Starting Level
FEED 1 y FEED 2:
-8.9 m (awl)
BRINE:
-7.8 m (awl)
Ending Level
FEED 1 y FEED 2:
-20.25 m (awl)
BRINE:
-25.5 m (awl)
Working Pressures
Up to 2 bar (feeds)
Up to 2.5 bar (brine)
TBM
Hydroshield AVN (Herrenknecht)
Intermediate Jacking Stations
FEED 1 y FEED 2:
12 each
BRINE:
17
BIBLIOGRAPHY