Influence of Initial Void Ratio on Critical State Behaviour of Poorly Graded Fine Sands
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ORIGINAL PAPER
Influence of Initial Void Ratio on Critical State Behaviour of Poorly Graded Fine Sands Abdullah Ekinci1
•
Mohamad Hanafi2
•
Pedro Miguel Vaz Ferreira3
Received: 29 August 2019 / Accepted: 30 January 2020 Ó Indian Geotechnical Society 2020
Abstract The application of critical state framework depends on the presence of either a unique critical state line (CSL). However, many authors have observed that a transitional behaviour occurs in certain granular intermediate soils in which the fines content and the initial void ratio have a significant effect on the location of this line. This work investigates these effects in poorly graded granular soils as previous studies reported that this type of soil does not exhibit transitional behaviour. Results from this study reveal that poorly graded fine-grained sand exhibits transitional behaviour similar to that of intermediate soils, and subsequently, it can be grouped into ranges of initial densities in which each group approaches a unique CSL in v:lnp’ space. A unique state boundary surface is identified by determining the critical state parameters from each group and using these parameters to normalise the stress paths; this shows that the critical state framework can be successfully applied to this type of soil.
& Abdullah Ekinci [email protected] Mohamad Hanafi [email protected] Pedro Miguel Vaz Ferreira [email protected] 1
Civil Engineering Program, Middle East Technical University, Northern Cyprus Campus, via Mersin 10, Kalkanli, Guzelyurt, North Cyprus, Turkey
2
Department of Civil Engineering, European University of Lefke, via Mersin 10, Lefke, North Cyprus, Turkey
3
University College London, Gower Street, London WC1E 6BT, UK
Keywords Fabric/structure of soil Laboratory test Sand
Introduction Characterising the behaviour of soil at high strains, or what is known as the critical state, is very important. This concept was first introduced by Casagrande [1], who discovered that during shearing, sand in a loose state decreases in volume, whereas sand in a dense state increases in volume until a critical void ratio is achieved. In their study on the yielding of soils, Roscoe et al. [2] concluded that each soil specimen has a particular critical pressure at which it will shear at constant volume when subjected to shear distortion. Furthermore, according to the critical state theory [3], when continuously distorted until they flow as frictional flow, soils or other granular materials will approach a welldefined critical state. Although the critical state was initially associated with clay, many authors have attempted to apply this concept to sandy soils [4–6]. However, the application of the critical state to sands is challenging owing to the difficulty of defining a virgin consolidation line for such soils [7] as well as the fact that compression in sand is influenced by stresses developed at the contact between the particles [8]. Nevertheless, some attempts to apply this concept to sands have been successful [9, 10]. In order to un
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