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Piling special: Spanish lessons from the Algeciras Port

Algeciras is Spain’s busiest port and it is set to increase its capacity following a series of expansion projects. Jo Stimpson reports on Balfour Beatty Ground Engineering’s role in the final phase.

This is not the first time that Balfour Beatty Ground Engineering (BBGE) has worked on the port of Algeciras with Spanish geotechnical contractor Geocisa.

In its former guise as Pennine, BBGE has already worked in a JV with Geocisa to complete three previous phases of the port’s expansion, dating back to 2004.

When Pennine was merged with two other constituents to become BBGE in April this year, the team simply hung a new banner on its barge and pressed on with the JV.

The JV’s success on the first and second phases of the expansion led to it winning work on the third and fourth.

“We have a good relationship with the client FCC Construccion and the port authority. We do all the jobs here in this port because they are very happy with our previous work,” says Geocisa industrial engineer Sergio González Flores.

The experience Geocisa and BBGE have gained from previous works at the port of Algeciras have not left the project free of challenges.

In fact, says BBGE international contracts engineer David Rickson, it drives the JV to live up to its own benchmarks. “We’re doing a similar sort of procedure so client FCC Construccion can compare this phase to previous phases,” he says.

The Aquacaster can create 30m deep columns

The Aquacaster can create 30m deep columns

On phases one and two, completed between 2004 and 2006, the JV was contracted to install a total of 1,759 vibro stone columns to support two separate lengths of quay wall that would, together with wall sections built by other contractors, enclose 106ha of new port space. In future, freight containers will be stored and cranes installed on this new land.

The third phase, completed in November 2009, involved the widening of an adjacent quay wall just to the north to facilitate a new oil pipeline. That pipeline will run to the new fuel vessel berth that is being constructed in phase four.

The phase three quay wall widening required 1,953 columns, and the phase four fuel berth needs 585. The soils on site comprise loose silty sands over soft silty clays at thicknesses between 4m and 30m.

The vibro stone columns are vital to improve the ground and ensure the integrity of the box caissons that will be built on top of them, and that there is no movement in the caisson wall.

“It’s to improve the bearing capacity of the soils, limit settlements and prevent against shear failure of the wall,” says BBGE international contracts engineer David Rickson.

The technique used in the latest phases of the project is simple and efficient, making use of BBGE’s in-house manufactured Aquacaster system, which is enabling the JV to build what it believes are the world’s deepest bottom feed marine columns to a maximum depth of 30m.

Strong westerly winds can cost the team a day of work, but the easterly weather tends to be much worse, stopping work for days or weeks at a time

The Aquacaster is a specially adapted version of BBGE’s HD150 vibroflot and features a 15m³ capacity hopper fixed at the top of a vibroflot. The hopper and vibroflot together are 36.5m in length and fitted to a crane that is anchored to a barge.

A separate hopper on the barge feeds the Aquacaster hopper, which takes on the locally sourced aggregate and deposits it continuously into the seabed through the bottom feed vibroflot.

Meanwhile, a water pump powered by a power pack on the barge takes up sea water and pumps it through the Aquacaster, aiding compaction of the ground and keeping the newly formed cavity open.

“The Aquacaster system holds the stone and deposits it when needed,” says Rickson. “It’s a simple but effective method.”

The main advantage of the technique is that it avoids extensive dredging, which would be time-consuming, expensive and environmentally harmful. “There’s less potential impact on marine ecology,” adds Rickson.

Using the Aquacaster to create vibro stone columns is also fast work compared to concrete piling − but only in the specific conditions where it is the appropriate method.

Once the columns are complete, a bedding layer of rubble is built up on top of them and levelled out in preparation for box caissons to be installed above it.

GPS helps with precision

GPS helps with precision

Thanks to the ground improvements made by BBGE and Geocisa, primary settlements of the treated ground during the construction stage are more or less finished by this point

The caisson bases are cast on barges atop a biodegradable paper layer to allow them to be removed from the barge over around seven hours.

The steel structure of the caisson is then built up before its sides are cast − tall enough for the caissons to protrude about 2m above water level − using a 200m long concrete pump pipe. “When they start building the caisson they can’t stop − it’s 24- hour working,” says González.

The caisson is then floated into place using GPS technology, and sunk by filling the cavity with water. Once all the caissons are in place, the water inside is replaced with aggregate.

The “sheer size of the vibroflot” meant the barge preparation posed quite a challenge, he says. If the 30m-long vibroflot were lifted incorrectly and without sufficient support, there was a danger of it snapping.

“To successfully get the equipment up and running was very rewarding following all our careful preparations”

David Rickson, BBGE international contracts engineer

Reinforcement plates were welded at potential weak points on the vibroflot connections. “To successfully get the equipment up and running was very rewarding following all our careful preparations,” says Rickson. “There are a lot of contingencies − people, the vibroflot, the cranes and the weather.”

The terrain of the site caused some logistical inconvenience. “We had to go further to fill the Aquacaster with stone,” says González.

At certain points, he explains, the sea depth is less than the length of the Aquacaster vibroflot, meaning that when such areas are being worked on the barge has to be moved out to deeper waters to enable the hopper to be filled before it can be moved back to treat the shallower areas.

Another logistical challenge was correctly locating the placement of the vibro stone columns. The operation of the vibroflot causes the water to cloud up, reducing visibility.

This problem was solved with the use of a GPS receiver fitted to the top of the crane cabin and another to the top point of the crane, allowing the operator to position the Aquacaster in precisely the right place, with a distance of 2.25m between each column.

A screen in the crane cabin shows a plan of the area with each column marked. “The driver can know at every moment which columns are done and which are left,” González says.

The software used on site also allows the driver to track the number of columns, the time that they were started, in refusal and completed, and to monitor the tide level changes throughout the day.

The Aquacaster's full length is 36.5m

The Aquacaster’s full length is 36.5m

But the real behemoth that has faced the team in Algeciras has been the weather. It is not just wind and waves that plague the site, says González. The swell of the sea is the real disruption.

Strong winds from the west are bad enough and can cost the team a day or so of work, he says, but the weather coming from the east tends to be much worse, stopping work for days or weeks at a time.

The completion date for phase four has been pushed back around two months from its original estimate, and is now at the end of May or beginning of June 2010. “It can rain full blast but if the swell’s okay we can get going,” says Rickson.

When NCE visited the site, columns were being installed on a pleasantly hot afternoon under a spotless blue sky. Towards the end of the day, however, the waters became noticeably choppier. “It’s changing to the east,” says González. “In a couple of hours we can’t stay here.”

The next morning, the sky was dark with clouds, the barges were secured against lashing winds, violent waves were crashing in the harbour and there were no workers to be seen on site.

Still, the team pushes on at every opportunity the weather gives them, and González says he is pleased with the JV’s work so far and with the ground settlement on phase three.

“The third phase has worked really well,” he says. No further phases of work are confirmed as yet and the next stage for the port will be for containers to be placed and cranes to be installed on the newly developed areas.

Geocisa and BBGE are also involved in works on a port in Sagunto on Spain’s east coast, where the JV also has past experience.

It may be a continuous struggle to tame the Spanish climate, but it seems the JV’s attempts to carve its particular niche in the market have proved much more successful.

Piling special: Spanish lessons from the Algeciras Port

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