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Discussion of "Determining soil plasticity utilizing Manafi method and Apparatus"

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o'Kelly, Brendan 
Vardanega, Paul 


The liquid limit (LL) of a fine-grained soil is widely understood as relating to the water content (w) at which the soil has a small remolded undrained shear strength (cu) (e.g. Wroth & Wood 1978). When the fall-cone apparatus is used to measure LL (i.e., 〖LL〗_FC), this can be shown to be true based on plasticity theory (Koumoto & Houlsby, 2001). Whilst when measured using the Casagrande-cup apparatus (i.e., 〖LL〗_cup) there is a small variation in cu at the LL (i.e., cu LL(cup)) of soils having different levels of plasticity owing to dissimilar soil bulk density (ρ) at their LL states, as demonstrated by Haigh (2012). For a given Casagrande-cup apparatus type, the 〖LL〗_cup actually relates to a constant specific strength (i.e., cu LL(cup)/ρ) magnitude (Haigh, 2012). However, the strength value at LL is not explicitly stated and thus, whilst it is demonstrable that the strength magnitude at LL is approximately constant, the LL w itself (i.e., 〖LL〗_FC and 〖LL〗_cup) is defined by the method prescribed by a testing standard used for obtaining it (e.g., ASTM D4318-17e1, 2018; BS EN ISO 17892-12:2018+A1:2021 2021), in addition to the specifics of the equipment design which may vary between countries (Haigh, 2016).



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Geotechnical Testing Journal

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ASTM International

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