Earlier this year, Bessac had completed, using its 3.50 m internal diameter microtunneling machine, the 183 m long hydraulic connection between the core of the pre-treatment plant and the storage tank (see newsletter dated 02/13/2020). Afterwards, the 98,000 m3 of ground were excavated and then evacuated at 94% by barges on the Seine river to reduce the disturbances linked to trucking.
Soletanche Bachy France therefore now needs to take over at the base of the basin, to construct the micropiles for anchoring the future slab.
The teams began drilling in October, all at a depth of 27m below the natural ground level. The schedule included 636 micropiles equipped with steel bars between 24m and 27m long, representing a total length of 18,000m to be drilled, at a diameter of 200mm.
Movement of machinery and equipment, as well as placing of the bars in the boreholes, is being carried out using a 300-tonne mobile crane stationed at the head of the tank and swinging over the imposing 72m-diameter structure. A well-oiled organisation is in place to successfully equip and seal as many micropiles as possible each day, while removing spoil from the head of the tank.
The last micropile is set to be installed in February 2021. The worksite will then be handed over to the civil engineering teams, which will reinforce and pour the slab.