The hydraulic performance and structural integrity of A-Jack armour layer

A-Jacks are concrete armor units that are used in both open channel and coastal applications.In open channel applications,they are used for bank and toe protection,flow and grade control,bridge pier scour protection,energy dissipation,and habitat.These small units may be fabricated in standard block machines.In coastal applications,A-Jacks are used in breakwaters,jetties,revetments,and habitat development.Coastal units are generally much larger and more robust than the small open channel units.This paper focuses on coastal applications and in particular,combines results on three topics: (1) recent hydraulic model studies, (2) ahemative fabrication methods,and(3) bundle placement construction methods.Hydraulic models studies were conducted that examined the standard random and uniform placement methods, and also the bundle placement method.In bundle placement, 3～20 A-Jacks are banded together,lifted with a spreader bar, and placed as a single crone pick.This significantly decreases installation time during construction.It also provides a more hydraulically stable placement technique.The hydraulic model tests examined the bundle stability fn random waves for cases where the binding remains in tack and is removed.The geometry of A-Jacks enables a variety of fabrication techniques.One option is to fabricate the A-Jacks as two pieces using flat forms and then grout the two pieces together.Flat forms may be used in conventional block machines for A-Jacks sizes up to 1.3 re.Larger sizes may be wet cast in flat forms or gang forms.The A-Jacks geometry has been recently modified to increase grouting efficient and strength.Large A-Jacks may also be east in a single piece using "clam shell" type forms.