• Offshore extension

Slight delays and small steps ahead of schedule

11 April 2018 - 15h52

The offshore extension site needs to adapt constantly in the face of new constraints and unfavourable weather conditions. While certain operations have seen slowdowns, others are proceeding without problems, and are even slightly ahead of schedule.

After around thirty round trips between Fos-sur-Mer and Monaco out of the fifty originally planned, the transportation of the quarried materials destined to form the backfill for the ring of caissons is in line with its planned schedule. At the end of March, more than 800,000 of the almost 1.5 million tons of this material had been sent. A new constraint has just been added, however: although the initial schedule called for the operation to be completed in July, with a three-week suspension during the Monaco Grand Prix, the plan is now to complete this task before the races. The Tiger, a ship that worked in the Principality a few months back, is therefore returning. Its role: to assist the fall pipe vessel Simon Stevin with its round trips between Fos and Monaco. Although its capacity is 10 times smaller (3,000 tons compared with 30,000), the Tiger will nonetheless help gain precious time and in theory, if meteorological conditions permit, at least, offer the opportunity of bringing the date of conclusion of the operation ahead of the automobile Grand Prix. This is a new challenge. If the objective is not attained, the Tiger will continue the work on its own so that the massive Simon Stevin can be demobilized before the automobile races start. At the same time, the Fabio Duo, an Italian barge owned by Sales of Piombino, has swung into action. She has the responsibility of delivering 40,000 tons of 5/50 materials (sizes between 5 and 50mm) but to be used to make the ballasted columns (a technique employed when there is a risk of soil liquefaction) only on the easternmost portion of the offshore extension: that is, on the Le Larvotto side. There is also another vessel at the site, the Mimar Sinan, which is continuing its task of removing the rocky outcrops, and which is scheduled to finish this mission in mid-April. Four vessels can therefore be seen in Monaco’s waters, each with its own function.

Microblasting trials

Below the Fairmont, the work to prepare placement of the heating and cooling outflow known as PP265 is continuing. This is a more delicate point. In fact, because weather conditions have not been favourable in recent weeks, it will take until the end of the month to complete the deck (see previous numbers) before beginning the next phase of the work: digging the trench. Another minor complication is the annoying presence of small rocky promontories at the entrance to the future pleasure marina. Microblasting trials – that is, setting off small underwater explosives – were carried out on 23rd March. “We’re happy with the results of this operation”, says Christophe Hirsinger, Director of Bouygues TP Monaco. “It was not foreseen, but it should go well, and will not cause any delays in our plans”.

The seventh caisson

In Marseille, construction of the caissons – 18 in all – is a source of great satisfaction. On 27th March, the seventh caisson, known as 8B, emerged from the caisson pre-casting facility. “We’re even seeing that we are slightly ahead of schedule”, says Christophe Hirsinger happily. The construction of concrete walls inside the caissons that was to be done in Monaco will therefore be carried out in Marseille instead in order to exploit this timesaving.

A barge blocked in England

With over half the backfill for the caissons having been brought from For, the first vibrocompacting operations should begin from mid-April. An 80-metre barge is scheduled to arrive shortly. Equipped with two huge 400 and 500 ton cranes, it will allow two large needles to be inserted into the soil. Vibrations from these needles will enable compacting of the backfill. The only unknown factor is that the barge is currently “blocked” in England due to difficult weather conditions; towing is expected to start again soon, however.

Georges-Olivier Kalifa

Photo © DR

 

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