diaphragm wall were subjected to bending in their primary iner- tia, which was per- fectly calculated by the 3D model structures. When the analyses necessary were com- plete to design the wall, it was time to begin construction. Excavating on a Steep Site View of the mountainous site To prepare for construction, the Vinci- Soletanche team performed several 2D and 3D analyses. First, a geotechnical 3D model was used to calculate the potential movements of the adjacent buildings, one of which was a middle school, and to verify the global stability of the slope. Then, the design team used 2D calculations to estimate, with better accuracy, the forces in the retaining walls at various stages of construction. Finally, a 3D structural model was used to review the structure during permanent conditions and particularly during simulated wind and earthquake activity. This 3D model took into account the position of the joints between panels, the embedments of the diaphragm wall and the barrettes with tangential stiffness. The panels of the 48 • DEEP FOUNDATIONS • JAN/FEB 2013 To prepare the small site, the hillside had to be excavated away to create a flat platform large enough for the tower to rise out of and the parking garage to drop into. The exca- vation for the platform had to be performed in three phases. First, the team had to excavate a series of steps into the top of the slope to create progressively l a r g e r w o r k i n g platforms that the excavators could then use to dig out the slope. The smallest platform, which was only 6 m (20 ft) wide, was just large enough for two Soilmec SM18 minipile rigs to work. The minipile rigs drilled a row of 52 piles, each 300 mm (12 in) in diameter and reinforced with a 220 mm (9 in) steel tube. These piles formed a retaining wall 15 m (50 ft) high at the back of the site. The slope was then removed, with six rows of anchors installed to support the wall as excavation proceeded. The anchors, which measured up to 40 m (132 ft) long, were carefully measured to stay within Monaco’s boundary so that the developer did not have to seek further permissions from the French authorities. If the anchors had crossed under the French border, which lies just at the back of the site, it could have been cause for an international incident. Completion of the minipile wall allowed another larger platform to be created with enough space to use a much larger piling rig, a Mait 240. Using this rig, the team installed 40 large, 1 m (3.28 ft) diameter piles, this time to a depth of 20m (66 ft). The spaced piles were the basis of a “Berlin wall” of piles used as kingpins with inter- mediate shotcrete lagging, finished with a concrete facing to support the marl hillside. This was followed by 8 rows of average 35 m (100 ft) long anchors, installed to support the “Berlin wall” as the hillside was excavated. The workers used the hydrofraise to excavate panels through the hard, marl limestone to average depths of 47 m (154 ft), and in some places, up to 55 m (180 ft). The soldier-micropile and soldier-pile walls are temporary structures, but the diaphragm wall will be permanent and will be supported by the parking floors, based on the top-down construction method. The superstructure will rest on the peripheral diaphragm wall and on several localized diaphragm walls within the excavation. Because the site is tight, the cages were fabricated off-site and trucked in. The width of each cage is limited and the reinforcement of each panel is subsequently made of three vertical cages. Workers lower each of these cages in the excavated trench filled with slurry. Design requires continuous horizontal reinforcement in each panel. The three cages are lifted out of the trench together and connected with horizontal rebars, which makes for an impressive lifting operation. The diaphragm wall’s ground heat energy extraction system further compli- cates construction. The system will act as a heating and/or cooling system that pumps heat to or from the ground through a special tubing system that runs inside of the reinforcement cages. Construction of the Odeon Towers is expected to take five years and is scheduled to be completed in the summer of 2014. When completed, the €500 million Odeon Tower will be the third tallest building in France, after the Montparnasse Tower, which rises 210 m (689 ft), and the Total Tower, which rises 187 m (613 ft).
