Incipient motion of Armorflex articulating concrete blocks on steep slopes

Delport, Kobus (2019-12)

Thesis (MEng)--Stellenbosch University, 2019.

Thesis

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.

AFRIKAANSE OPSOMMING: Armorflex is ‘n metode wat as ‘n alternatief vir stortklip vir baie jare gebruik word om erosie te voorkom. Ondanks die omvattende navorsing en hidrouliese toetse was reeds op Armorflex gedoen is, bly daar steeds ‘n mate van onsekerheid in die limiete van Armorflex in kanaalvloei toepassings. Boonop is daar geen standaarde wat gespesifiseer is vir die gebruik van Armorflex in SANS nie. The hoofdoelwit van hierdie studie is om die kritieke faktore wat beweging van Armorflexblokke in kanaalvloei toepassings veroorsaak, beter te verstaan. Armorflex 140 en Armorflex 180 word spesifiek bestudeer. Verskillende metodes wat die begin van beweging voorspel en beskryf word ondersoek, met Liu se teorie van 1957 wat van spesifieke belang is. Geskaalde laboratoriumtoetse is gedoen om die toepaslikheid van Liu se teorie op Armorflex-blokke te bepaal. Vir partikel Reynolds getalle tussen 11025 en 131397, dui die resultate van die studie op Mobiliteitsgetalle van 0.249 en 0.220 vir Armorflex 140 en 180 op bodemhellings. ‘n Dimensielose stabiliteitsfaktor van 1.47 en 1.33 kan onderskeidelik op Armorflex 140 en 180 toegepas word vir blokke op kanthellings. Die resultate verkry vanaf die laboratoriumtoetse is vergelyk met die ontwerpriglyne van die Armorflex vervaardigers Technicrete (2016) en Contech Construction Products inc. (Armortec Incorporated, 1981). Die Armorflex produkbrosjure van Technicrete (2016) bied ‘n maksimum helling van 1V:1.5H en vloeisnelheidslimiete as ontwerpriglyne, terwyl Contech Construction Products inc. (Armortec Incorporated, 1981) vloeisnelheid asook hidrouliese radius by verskillende bodemhellings gebruik om die limiete van Armorflex te beskryf. Die resultate van die studie toon dat Technicrete se ontwerpriglyne van 3.5 m/s en 5.5 m/s vir Armorflex 140 en 180 blokke moontlik oorgeskatte waardes is vir blokke op bodemhellings. Blokke op kanthellings het wel kritiese vloeisnelhede getoon wat soortgelyk is aan die limiete van Technicrete. Die vergelyking van die laboratoriumtoetsresultate met die ontwerpriglyne van Contech Construction Products inc. (Armortec Incorporated, 1981) toon dat geen blokfalings bereik is teen vloeisnelhede laer as die ontwerpriglyne nie. Literatuur toon dat vloeisnelheid nie ‘n gepaste parameter is om die voorwaardes vir beweging van kohesielose partikels te voorspel nie. Die Armorflex ontwerpriglyne van Technicrete (2016) en Contech Construction Products inc. (Armortec Incorporated, 1981) in terme van ‘n maksimum vloeisnelheid alleen kan dus nie gebruik word vir die ontwerp van Armorflex strukture nie. Hierdie tesis skryf Liu se Mobiliteitsgetal voor as die gekose metode om die punt van beweging van Armorflex-blokke te bepaal. Die resultate van die studie is gebruik om ‘n Microsoft Excel model te ontwikkel vir die veilige ontwerp van Armorflex kanale. Die berekende Mobiliteitsgetalle van Armorflex-blokke is hoër as die Mobiliteitsgetalle van stortklip en Reno-matrasse wat deur navorsers voorgeskryf word. Anders as Armorflex, bevat stortklip en Reno-matrasse partikels wat kleiner is as die ontwerpsgrootte wat makliker weggespoel kan word deur vloeiende water en wat moontlik kan lei tot die ondermyning van die groter partikels. Die Mobiliteitsgetalle voorgestel in hierdie tesis is ook hoër as Rooseboom & van Vuuren (2013) se Mobiliteitsgetal van 0.12 vir betonblokkanale.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/107161
This item appears in the following collections: