Geotech Report - Initial Findings

Notes on Description and Classification of Soil
Revision 3, November 2008




        Notes on Description and Classification of Soil
        The methods of description and classification of soils used in this report are generally based on Australian Standard AS1726-1993
        Geotechnical Site Investigations.

        Soil description is based on an assessment of disturbed samples, as recovered from bores and excavations, or from undisturbed
        materials as seen in excavations and exposures or in undisturbed samples. Descriptions given on report sheets are an interpretation of
        the conditions encountered at the time of investigation.

        In the case of cone or piezocone penetrometer tests, actual soil samples are not recovered and soil description is inferred based on
        published correlations, past experience and comparison with bore and/or test pit data (if available).

        Soil classification is based on the particle size distribution of the soil and the plasticity of the portion of the material finer than 0.425mm.
        The description of particle size distribution and plasticity is based on the results of visual field estimation, laboratory testing or both.
        When assessed in the field, the properties of the soil are estimated; precise description will always require laboratory testing to define
        soil properties.

        Where soil can be clearly identified as FILL this will be noted as the main soil type followed by a description of the composition of the fill
        (e.g. FILL – yellow-brown, fine to coarse grained gravelly clay fill with concrete rubble). If the soil is assessed as possibly being fill this
        will be noted as an additional observation.

        Soils are generally described using the following sequence of terms. In certain instances, not all of the terms will be included in the soil
        description.

        MAIN SOIL TYPE (CLASSIFICATION GROUP SYMBOL)
        - strength/density, colour, structure/grain size, secondary and minor components, additional observations


        Information on the definition of descriptive and classification terms follows.

        SOIL TYPE and CLASSIFICATION GROUP SYMBOLS

                                                                                         Classification
                                        Major Divisions             Particle Size                                       Typical Names
                                                                                         Group Symbol
                                          BOULDERS                   > 200mm
                                           COBBLES                  63 – 200mm
                                                                                                          Well graded gravels, gravel-sand mixtures,
                                                                                              GW
                                          GRAVELS                                                                           little or no fines.
                                                                Coarse: 20 – 63mm
                                      (more than half of                                                     Poorly graded gravels and gravel-sand
                                                                Medium: 6 – 20mm              GP
                                                                                                           mixtures, little or no fines, uniform gravels.
                                    coarse fraction is larger
                                                                 Fine: 2.36 – 6mm
               COARSE                   than 2.36mm)                                          GM             Silty gravels, gravel-sand-silt mixtures.
           GRAINED SOILS                                                                      GC           Clayey gravels, gravel-sand-clay mixtures.
           (more than half of                                                                              Well graded sands, gravelly sands, little or
          material is larger than                                                             SW
                                            SANDS                                                                                 no fines.
               0.075 mm)                                  Coarse: 0.6 – 2.36mm
                                      (more than half of                                                   Poorly graded sands and gravelly sands;
                                                          Medium: 0.2 – 0.6mm                 SP
                                                                                                                  little or no fines, uniform sands.
                                       coarse fraction is
                                                           Fine: 0.075 – 0.2mm
                                     smaller than 2.36mm)                                     SM                   Silty sands, sand-silt mixtures.
                                                                                              SC                Clayey sands, sand-clay mixtures.
                                                                                                                Inorganic silts and very fine sands,
                                                                                              ML            silty/clayey fine sands or clayey silts with
                                                                                                                              low plasticity.
                                        SILTS & CLAYS
                                                                                                          Inorganic clays of low to medium plasticity,
                                       (liquid limit <50%)                                 CL and CI
                                                                                                             gravelly clays, sandy clays, silty clays.
                                                                                                           Organic silts and organic silty clays of low
                   FINE                                                                       OL
                                                                                                                                 plasticity.
           GRAINED SOILS                                                                                  Inorganic silts, micaceous or diatomaceous
           (more than half of                                                                 MH
                                                                                                                        fine sandy or silty soils.
         material is smaller than       SILTS & CLAYS
                                                                                              CH                 Inorganic clays of high plasticity.
               0.075 mm)               (liquid limit >50%)
                                                                                                           Organic clays of medium to high plasticity,
                                                                                              OH
                                                                                                                               organic silts.
                                      HIGHLY ORGANIC
                                                                                               Pt             Peat and other highly organic soils.
                                           SOILS




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