Genesis of transitional behaviour in geomaterials: a review and gap analysis

ABSTRACT

There has been sporadic but increasing reporting regarding the intermediate character of natural geomaterials which neither conforms to the general behaviour of fine-grained (clay-like) nor coarse-grained (sand-like) soils. Nonetheless, geoscience considers such soils as non-textbook or challenging geomaterials. The literature attempts to identify and analyse a range of threshold manifestations of their behaviour (e.g. liquefaction). However, the physics behind their transient nature is not described in a generic manner. Transitional behaviour (TB) is observed more often in soils containing measurable amounts of silt-size particles. The complexity of their structure – greatly dependent on a number of interrelated micro and macro parameters – is believed to discourage generalisation of the behaviour. This review collates the factors potentially controlling the reported transient character. In order to illustrate a more holistic picture of transitional soils, the available characterisation findings are critically categorised based on purpose and/or testing technique. Collective understanding of transitional soils can ultimately provide a more confident prediction of their ramifications in a wide spectrum of applications. The present initiative is meant to attract attention to the need for multidisciplinary research on quantifying the controversial character of this class of geomaterials. It is also attempted to highlight relevant discrepancies and identify research gaps.

KEYWORDS:

• Transitional behaviour
• silt-size particles
• soil structure
• micro and macro parameters
• discrepancies
• gap analysis

Notations

The following summarises the common abbreviations, acronyms, definitions and parameters used throughout this paper:

b	=	a parameter that denotes the portion of the fine grains that contributes to the active intergrain contacts;
CD	=	consolidated-drained triaxial test;
CF	=	clay fraction (%);
CSL	=	critical state line $\left(\nu =\mathrm{\Gamma }-\lambda ln{p}_{cs}^{\prime }\right)$;
CRR	=	cyclic resistance ratio;
CSR	=	cyclic stress ratio;
CU	=	consolidated-undrained triaxial test;
$C_c$	=	coefficient of curvature;
$C_u$	=	coefficient of uniformity;
D50-silt	=	mean size of silt fraction;
Dmax	=	largest identifiable coarse particles from microimages;
$e$	=	global void ratio;
$e_c,(e_c{)}_{eq}$	=	intergranular and equivalent intergrain contact void ratio, respectively;
$e_f,(e_f{)}_{eq}$	=	interfine and equivalent interfine contact void ratio;
$e_{\hspace{0.17em}}$	=	critical state line intercept with void ratio axis at $p\prime$ of 1 kPa
FC	=	fines content,
FCth	=	threshold fines content;
ICL	=	isotropic consolidation line $\left(\nu =N-\lambda ln{p}^{\prime }\right)$;
$I_P$	=	plasticity index;
LFC or FCL	=	limiting fine content (%);
MWD	=	mean weigh diameter $=\underset{i=1}{\overset{n}{\mathrm{\Sigma }}}{x}_i{\omega }_i$ ($x_i$: mean diameter of any particular size range, ${\omega }_i$: weight of soil in that size range as a fraction of the total dry weight);
MWDsilt	=	mean weight diameter of silt fraction;
NCL	=	normal consolidation line;
OCR	=	over consolidation ratios;
$p^{\prime }$	=	effective mean stress;
$p_{cs}^{\prime }$	=	effective mean stress at critical stress;
$q$	=	deviatoric stress;
S	=	$\frac{\mathrm{\#}StableContacts}{\mathrm{\#}UnstableContacts}$
SEM	=	scan electron microscopy;
TB	=	transitional behaviour;
USDA	=	United States Department of Agriculture;
UU	=	undrained unconsolidated test;
$\lambda$	=	critical state line gradient in the $e-lnp$ plane; and
$\nu$	=	specific volume;

Disclosure statement

No potential conflict of interest was reported by the authors.