Compiled Reference Documents - OPW25/0053 (As Published)

                                                                                                   Terminology
    Soil Descriptions                                                                                 Symbols
                                                                                                  Abbreviations
                                                                                                                      March 2024



Introduction
All materials which are not considered to be “in-situ rock” are described in general accordance with the soil
description model of AS 1726-2017 Part 6.1.3, and can be broken down into the following description
structure:

                             classification
                                              name                detailed description

                                  (SC) Clayey SAND, trace silt; grey, fine to medium grained

The “classification” comprises a two character “group symbol” providing a general summary of dominant
soil characteristics. The “name” summarises the particle sizes within the soil which most influence its
behaviour. The detailed description presents more information about composition, condition, structure,
and origin of the soil.
Classification, naming and description of soils require the relative proportion of particles of different sizes
within the whole soil mixture to be considered.

Particle size designation and Behaviour Model
Solid    particles  within     a     soil are Particle Size                  Particle             Behaviour Model
differentiated on the basis of size.          Designation                       Size          Behaviour Approximate
                                                                               (mm)                         Dry Mass
The engineering behaviour properties of a
                                                       Boulder             >200               Excluded from particle
soil can subsequently be modelled to be
                                                       Cobble              63 - 200           behaviour model as
either “fine grained” (also known as
                                                                                              “oversize”
“cohesive” behaviour) or “coarse grained”
(“non cohesive” behaviour), depending on               Gravel1             2.36 - 63
                                                                                              Coarse         >65%
the relative proportion of fine or coarse              Sand1               0.075 - 2.36
fractions in the soil mixture.                         Silt                  0.002 - 0.075
                                                                                                Fine         >35%
                                                        Clay                 <0.002
                                                      1
                                                        – refer grain size subdivision descriptions below
The behaviour model boundaries defined above are not precise, and the material behaviour should be
assumed from the name given to the material (which considers the particle fraction which dominates the
behaviour, refer “component proportions” below), rather than strict observance of the proportions of
particle sizes. For example, if a material is named a “Sandy CLAY”, this is indicative that the material exhibits
fine grained behaviour, even if the dry mass of coarse grained material may exceed 65%.

Component proportions
The relative proportion of the dry mass of each particle size fraction is assessed to be a “primary”,
“secondary”, or “minor” component of the soil mixture, depending on its influence over the soil behaviour.
      Component                        Definition1                                 Relative Proportion
       Proportion                                                     In Fine Grained Soil      In Coarse Grained
      Designation                                                                                      Soil
    Primary              The component (particle size                The clay/silt            The sand/gravel
                         designation, refer above) which             component with the       component with the
                         dominates the engineering                   greater proportion       greater proportion
                         behaviour of the soil
    Secondary            Any component which is not the              Any component with              Any granular
                         primary, but is significant to the          greater than 30%                component with
                         engineering properties of the soil          proportion                      greater than 30%; or
                                                                                                     Any fine component
                                                                                                     with greater than
                                                                                                     12%
    Minor2               Present in the soil, but not                All other components            All other
                         significant to its engineering                                              components
                         properties
1
 As defined in AS1726-2017 6.1.4.4
2
 In the detailed material description, minor components are split into two further sub-categories. Refer “identification of minor
components” below.

Composite Materials
In certain situations, a lithology description may describe more than one material, for example, collectively
describing a layer of interbedded sand and clay. In such a scenario, the two materials would be described
independently, with the names preceded or followed by a statement describing the arrangement by which
the materials co-exist. For example, “INTERBEDDED Silty CLAY AND SAND”.


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