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Armorflex is an articulating concrete block erosion protection measure that has been used as an alternative to riprap for many years. Even though extensive research and hydraulic testing have been conducted on Armorflex, the principal constraint on the use of concrete blocks has been the lack of information on prototype performance. Furthermore, there are no standards for Armorflex or articulating concrete block revetments in the South African National Standards, and design guidelines from Armorflex manufacturers are insufficient. The aim of this study was to improve the understanding of the critical flow conditions under which Armorflex blocks are lifted and removed by flowing water in open channel flow applications. Scaled laboratory tests were conducted on Armorflex 140 and Armorflex 180 blocks. Liu's theory of 1957 is applied in an attempt to define the point where block movement is initiated. [ABSTRACT FROM AUTHOR]

Liu's theory of 1957 to estimate the point of incipient motion, derived assuming a flat bed slope and uniform flow, states that for large particles the movability number (defined as the ratio of the shear velocity to the settling velocity), is constant. Data collected from 12 undistorted and unscaled laboratory tests was used to investigate the applicability of the theory on steep riprap slopes. The tests indicate that the dimensionless movability number (MN) is constant for large particle Reynold numbers. For design purposes, the recommended movability number which emerged from this study is 0.18, provided that the steep bed slope is taken into account, the energy slope is considered in MN, and that the theoretical settling velocity is calculated using an accurate drag coefficient and the d90 sieve size of the riprap. [ABSTRACT FROM AUTHOR]