Geotechnical Investigation Of Dry Docks No.2 And No.3 At The Brest Naval Base (France)2002 Dr Baden Clegg Award Winner

Frederic Verheyde

During 2000 and 2001, Fondasol, a French geotechnical consulting company, carried out two geotechnical investigations over a combined period of 5 months, concerning dry docks No.2 and No.3 at the Brest naval base (France). As the project manager, I will present this study. The paper will cover the geometry of the structure, and provide an overview of its history and description of its current state. I will then deal with the main objectives of the investigation, the different techniques used during the field work and the main results.

Dry docks No.2 and No.3 of Brest naval base are each about 180 m long, 33 m wide and 13.5 m deep. They lie adjacent to each other, separated by a central mole of 20 m in width. Each dry dock can be closed by a floating and sinking steel gate, which isolates the structure from the harbour, subject to an 8 m tide twice daily.

The construction of the structure began in 1746 by driving 7400 wooden piles into a muddy bay and resulted six years later in three small dry docks which were constructed partially on wooden piles and partially excavated into rock. The three dry docks had a total length of 130 m and a total width of 8.5 m (Figure 1). The boundaries between the two types of foundation were unknown at the time the investigation was carried out. Major modifications of the structure were carried out on four separate occasions, resulting in the dry docks reaching their current arrangement of two 180 m long dry docks by 1901. Apart from two large explosions that affected the entrance of the structure during the Second World War, no significant changes have been made since.