This study investigates how the loading procedure, the type of device and the wearing of the interfaces affect the friction angle of geosynthetics. Four interfaces were tested, two showing a gradual sliding behaviour (A and B) and two a sudden sliding behaviour (C and D): GGR-GCD (A), GTX-GMBPP (B), GTX-GMBHDPE (C), GCD- GMBHDPE (D). These interfaces were tested both on the inclined plane device (IP) and on the horizontal plane device (HP) considering incremental cumulated displacements to take into account the effect of the wearing of the surfaces. Three loading methods were considered: the first considers a continuous increase at a constant rate of the shear stress, following the European Standard procedure ISO 12957-2 for the inclined plane and the equivalent Shear Stress Increase procedure for the horizontal plane, the second involves a discontinuous increase of the shear stress following a new type of procedure here called “step procedure” and the third apply a constant shear stress during long tests to check the estimations given by the other two types of procedures. The fact that those loading procedures were all stress-controlled and equivalent between the two devices allowed the comparison between results obtained with different types of devices. The results showed a systematic discrepancy between IP and HP tests with the formers reporting higher friction angles respect to the latter. The results also showed, for both IP and HP, that the step procedure gives significantly lower friction angles respect to the current European Standard, especially for gradual sliding interfaces. This fact is explained by the increase of interface shear stress with sliding speed and suggests that a revision of the current standard may be necessary. The results also confirmed that the effect of the wearing on the friction parameter greatly varies with the type, surface finish and materials of the interfaces: for example, interface A showed an increase of the friction with the cumulated displacement due to the increased interaction between worn-out GCD fibres with GGR while interfaces C and D showed a decrease of friction due to the smoothing of the GMB surface.
Questo studio investiga come la procedura di carico, il tipo di apparato sperimentale e l’usura delle interfacce influisce sull’angolo di attrito dei geosintetici. Sono state testate quattro interfacce, due caratterizzate da uno scorrimento graduale (A e B) e due da uno scorrimento non graduale (C e D): GGR-GCD (A), GTX-GMBPP (B), GTX-GMBHDPE (C), GCD- GMBHDPE (D). Queste interfacce sono state testate sia sul dispositivo a piano inclinato (IP) che sul dispositivo a piano orizzontale (HP) considerando gli spostamenti cumulati incrementali in modo da valutare l’effetto dell’usura delle superfici. Sono state considerate tre procedure di carico: la prima considera un incremento costante dello sforzo di taglio, seguendo la procedura Standard Europea ISO 12957-2 per il piano inclinato e la procedura equivalente SSI (taglio a incremento di forza) per il piano orizzontale, la seconda considera un incremento discontinuo dello sforzo di taglio seguendo un nuovo tipo di procedura chiamata “procedura a step” e la terza considera uno sforzo di taglio costante durante test di lunga durata in modo da verificare le stime ottenute tramite gli latri due tipi di procedure di carico. Il fatto che tutte queste procedure di carico siano controllate dallo stress applicato e che siano equivalenti tra i due tipi di dispositivi usati permette di comparare i risultati ottenuti. I risultati mostrano una discrepanza sistematica tra i test sul piano inclinato e quelli sul piano orizzontale con i primi che mostrano angoli di attrito maggiori dei secondi. I risultati ottenuti mostrano anche che, per entrambi i tipi di apparato sperimentale, la procedura a step produce angoli di attrito significativamente minori rispetto all’attuale procedura Standard, specialmente per le interfacce a scorrimento graduale. Questo fatto si spiega con l’incremento dell’attrito con la velocità di scorrimento e suggerisce che una revisione dell’attuale Standard Europeo sia necessaria. I risultati confermano anche che l’effetto dell’usura dipende largamente dal tipo di interfaccia, dalla finitura superficiale e dal tipo di materiali utilizzati: per esempio, l’interfaccia A ha mostrato un aumento dell’angolo di attrito con lo spostamento cumulato a causa della maggiore interazione tra le fibre del GCD con la GGR mentre, al contrario, le interfacce C e D hanno mostrato una diminuzione di tale parametro a causa della levigatura della superficie della GMB.
Modalità di carico e resistenza di interfaccia tra geosintetici
DI CHIO, FEDERICO
2021/2022
Abstract
This study investigates how the loading procedure, the type of device and the wearing of the interfaces affect the friction angle of geosynthetics. Four interfaces were tested, two showing a gradual sliding behaviour (A and B) and two a sudden sliding behaviour (C and D): GGR-GCD (A), GTX-GMBPP (B), GTX-GMBHDPE (C), GCD- GMBHDPE (D). These interfaces were tested both on the inclined plane device (IP) and on the horizontal plane device (HP) considering incremental cumulated displacements to take into account the effect of the wearing of the surfaces. Three loading methods were considered: the first considers a continuous increase at a constant rate of the shear stress, following the European Standard procedure ISO 12957-2 for the inclined plane and the equivalent Shear Stress Increase procedure for the horizontal plane, the second involves a discontinuous increase of the shear stress following a new type of procedure here called “step procedure” and the third apply a constant shear stress during long tests to check the estimations given by the other two types of procedures. The fact that those loading procedures were all stress-controlled and equivalent between the two devices allowed the comparison between results obtained with different types of devices. The results showed a systematic discrepancy between IP and HP tests with the formers reporting higher friction angles respect to the latter. The results also showed, for both IP and HP, that the step procedure gives significantly lower friction angles respect to the current European Standard, especially for gradual sliding interfaces. This fact is explained by the increase of interface shear stress with sliding speed and suggests that a revision of the current standard may be necessary. The results also confirmed that the effect of the wearing on the friction parameter greatly varies with the type, surface finish and materials of the interfaces: for example, interface A showed an increase of the friction with the cumulated displacement due to the increased interaction between worn-out GCD fibres with GGR while interfaces C and D showed a decrease of friction due to the smoothing of the GMB surface.File | Dimensione | Formato | |
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LOADING EFFECT ON GEOSYNTHETIC INTERFACE STRENGHT.pdf
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https://hdl.handle.net/20.500.12608/33264