The concept of ductility or brittleness has commonly used in civil engineering when steel, concrete, or structure has been examined. However, the geotechnical researchers have focused rarely on this aspect of soil.
Soil structure is not possible to classify as ductile or too brittle. But we can evaluate that Resilient Modulus (Mr) is a value, degree of flexibility at pavement design. For example, cohesive soils have a lower Mr value when comparing to non-cohesive soils such as sand, gravel class . Of course, axe load type or repetition is important for this stage; cohesive soil is mainly intended axle load, so if it increases, more ductile behavior is observed. But this situation is reverse for non-cohesive soils.
The soil modulus and the strain at failure as determined from the stress strain curves from the triaxial test will give a good indication .Sandy samples will low modulus value E,large strain at failure and no peak strength value will indicate loose,compressible, and ductile behavior. Sands with very large modulus and low strain at failure will indicate very dense, cemented fabric , or brittle conditions
Brittle behavior of sandy soils is usually most influenced by weak cementation, usually carbonate. If the region you are working in receives less than 500 mm of annual precipitation, carbonate is usually precipitated in the upper few meters of the exposed ground surface. Complicating factors can be "cold welding" of quartz grains, but this only occurs under significant confinement and compression. Another complicating factor can be the presence of silt in the sandy soil matrix, which, upon wetting, can engender sufficient lubrication to hasten collapse of the soil fabric in semi-arid climes (areas receiving < 500 mm annual precipitation) .
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M. Neaz Sheikh, M. Mashiri, J. Vinod, and H. Tsang, "Shear and Compressibility Behavior of Sand–Tire Crumb Mixtures," Journal of Materials in Civil Engineering, vol. 25, pp. 1366-1374, 2013/10/01 2012.
I suppose Atterberg limits can give an intuitive indication, Also, there exists a lot of literature on correlation between index properties and meaningful physics based properties.
Ductility and brittleness are not properties that are usually being sought for in soil but the property that has a relationship with these is swelling and volumetric shrinkage properties of soil though ductility and brittleness can be determined when dealing with reinforcement and concrete. Sandy soils usually have lower swelling and volumetric shrinkage than clayey soil, hence one can juxtapose this with respect to ductility and brittleness.
For Soils the the brittle and ductile behaviour is rarely using, even though these things are described in some Geotechnical Engg. Text Books
I think that a reason why the researchers have rarely considered the soils in terms of brittleness and ductility is that the majority of sample preparations are based on the reconstituted samples. And the undisturbed samples have not commonly used in the geotechnical laboratory because the extracting samples from the field can be so expensive, and working with such samples can be so difficult to handle.
Therefore, if the reconstituted and undisturbed samples are investigated together, then the undisturbed samples may indicate brittle behavior, but the reconstituted samples may indicate ductile behavior.
Yes the best parameters are brittleness index and deformability index. Read the paper of "Influence of Cement Treatment on Unconfined Compressive
Strength and Compressibility of Lean Clay withMedium Plasticity".
Yes, there is an important parameter in undrained behaviour of sandy soil named as brittlness index which you could be caculated from plot of deviator stress with effective mean pressure to show the response of soil.
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