Browsing by Author "Delport, Kobus"

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    Incipient motion of Armorflex articulating concrete blocks on steep slopes
    (Stellenbosch : Stellenbosch University, 2019-12) Delport, Kobus; Basson, G. R.; Bosman, Adèle ; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
    ENGLISH ABSTRACT: Armorflex is an articulating concrete block erosion protection measure that has been used as an alternative to riprap (dumped rock) 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 SANS. The aim of this study is to improve the understanding of the critical flow conditions under which Armorflex blocks are lifted up and removed by flowing water in open channel flow applications. Armorflex 140 and Armorflex 180 blocks are studied in particular. Liu’s theory (1957) of incipient motion is of primary interest and is applied in an attempt to define the point where block movement is initiated. Scaled laboratory tests were conducted to determine whether Liu’s theory holds for Armorflex blocks. For particle Reynolds numbers between 11025 and 131397, the results from the study indicate respective Movability Numbers of 0.249 and 0.220 for Armorflex 140 and 180 installed on bed slopes. Dimensionless stability factors of 1.47 and 1.33 can respectively be applied to Armorflex 140 and 180 blocks installed on side slopes. The results from the laboratory tests were compared with the manufacturer design guidelines of Technicrete (2016) and Contech Construction Products inc. (Armortec Incorporated, 1981). Technicrete (2016) provides a maximum desired slope of 1V:1.5H and limiting flow velocities only, while Contech Construction Products inc. (Armortec Incorporated, 1981) includes flow velocities and hydraulic radius at varying bed slopes as limiting parameters. The results proposed that Technicrete’s respective limiting flow velocities of 3.5 m/s and 5.5 m/s for Armorflex 140 and 180 blocks may be an overestimation for blocks installed on bed slopes. On side slopes, however, failure was observed at flow velocities similar to the limits stated by Technicrete. Comparing the laboratory findings to the limiting velocity guideline of Contech Construction Products inc. (Armortec Incorporated, 1981), no block failures were achieved at flow velocities lower than the design guideline velocities. According to incipient motion theory, however, flow velocity is not a suitable parameter for defining incipient motion. Therefore, the limiting flow velocity guidelines of Technicrete (2016) and Contech Construction Products inc. (Armortec Incorporated, 1981) alone cannot be used to design Armorflex lined structures in practice. Instead, this thesis recommends the use of Liu’s Movability Number to determine the point of incipient motion of Armorflex. The results from the study were used to develop a Microsoft Excel model for the safe design of Armorflex-lined drainage channels. The Movability Numbers of Armorflex blocks obtained in this study are greater than the Movability Numbers recommended by researchers for riprap (dumped rock) and Renomattresses. Unlike riprap and Reno-mattresses, Armorflex has no particles smaller than the design weight that can be washed away by forces of flowing water, undermining the larger particles. The Movability Numbers presented in this thesis are also greater than Rooseboom & van Vuuren's (2013) recommended Movability Number of 0.12 for articulating concrete blocks.