The tool offers the possibility of cutting the soil with the drill pipe and, in the case of the secant pile technique, overlapping and improving verticality. This solution offers a decisive advantage for retaining structures under groundwater or in a marine environment; relative watertightness conforming to DTU 14.1 between the reinforced concrete piles created by alternating a primary pile and a secondary pile. The primary is cast either with mortar, grout or non-reinforced concrete, and the secondary has a reinforcement cage. The secondary piles are set up by overlapping the previously laid primary piles. The possibility of using the double-rotary technique limits deviations in the verticality of the drilling in the primary pile. The technicality and high rates inherent in hollow auger work made this solution a must on the Anse du Portier (i.e. “Portier Cove”).
Handled by Bouygues TP’s Monaco subsidiary, the worksite involves the construction of a seaward extension to create new land. The construction principle is proven: reinforced concrete caissons filled with 20/180 granulometry materials are submerged on a bed of previously laid materials. To the far west of the structure, Franki Fondation is tasked with building small sea walls mainly out of secant piles and a few isolated piles. After earthworks, they will form the marina’s permanent retaining structures.
The context suits the use of a technique allowing simultaneous tubing and drilling, but hollow augers are still a good option, too. The advantage? Rates high enough to guarantee meeting the contractual deadline. It’s a major constraint of the project, which also is regulated in terms of strict tolerances in terms of not only noise but also all disturbances and widespread parallel activities on a highly cramped site. “Due to an average depth of 20m per pile, the drilling rig is capable of setting up 3 to 4 piles per day, with a concreting time not exceeding 20 minutes per pile.”
From mid-April to mid-July, the team set up eighty-five 820mm-diameter piles, drilled 1,200Lm and theoretically used 600m3 of concrete (actually 1,500m3) and 90T of steel.
General contractor: Bouygues TP + EGIS
Project owner: Anse du Portier
Sub-contractor of Bouygues TP MONACO
