Containment dykes basal reinforcement

Basal reinforcement beneath breakwaters and containment dykes... 

Figure 20.19 Basal reinforcement technique applied to breakwaters and containment dykes on soft foundations.

One technique to improve the stability of breakwaters and containment dykes con-stmcted on soft foundations is to use geotextile reinforcement across the base of the stmcture (Fig. 20.19). This basal reinforcement technique has been used successfully for many years in the onshore construction of embankments on soft foundation soils, and is discussed in detail in chapter Geotextiles used in reinforcing foundations. Because of its cost—benefits, this technique has also been used in marine engineering structures over the past 20 years. 

Figure 20.20 Design limit modes for basal reinforced breakwaters and containment dykes on soft foundations, (a) HydrauUc stabiUty, (b) rotational stabiUty, (c) strain in reinforcement and (d) settlement.

Ameratunga et al. (2006) describe the design and construction of a basal-reinforced rubble seawall (containment dyke) over soft marine clay for the expansion of the Port of Brisbane, Australia. Fig. 20.21 shows a typical cross section of the basal-reinforced rabble seawall. The seawall was constructed to contain the reclamation fill for the port expansion. The thickness of the soft foundation varied from 8 to 30 m in some locations it had an undrained shear strength as low as 5 kPa at the foundation surface which was approximately 3.5 m below the average water depth. The rabble seawall varied in height to 7.5 m, and an analysis showed that the soft foundation could not support this... 

Historically, containment dykes were constructed using rubble fill (Fig. 20.24(a)). The rubble fill is placed on the seabed and forms the erosion-resistant boundary. If the seabed is soft, a geotextile separation layer or basal reinforcement layer may be placed before the rubble fill is placed on top. A geotextile filter is placed on the inside face of the rubble fill to prevent erosion of the reclamation fill material through the coarse mbble fill in the dyke. Finally, rock armouring is placed outside the rubble fill dyke to prevent damage from coastal water forces. Fig. 20.25 shows an example of a rubble fill containment dyke with a geotextile filter placed on the inside face before placement of the reclamation fill. 

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