Geotech Report - Initial Findings

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




        PLASTICITY CHART FOR CLASSIFICATION OF FINE GRAINED SOILS




        (Reference: Australian Standard AS1726-1993 Geotechnical site investigations)


        DESCRIPTIVE TERMS FOR MATERIAL PROPORTIONS

                             Coarse Grained Soils                                                   Fine Grained Soils
          % Fines                            Modifier                        % Coarse                             Modifier
            <5                         Omit, or use „trace‟                    < 15                          Omit, or use trace.
           5 – 12           Describe as „with clay/silt‟ as applicable.       15 – 30          Describe as „with sand/gravel‟ as applicable.
            > 12            Prefix soil as „silty/clayey‟ as applicable        > 30            Prefix soil as „sandy/gravelly‟ as applicable.


        STRENGTH TERMS – COHESIVE SOILS

            Strength             Undrained Shear
                                                                                          Field Guide to Strength
             Term                   Strength
            Very soft                < 12kPa                                 Exudes between the fingers when squeezed in hand.
              Soft                  12 – 25kPa                                     Can be moulded by light finger pressure.
              Firm                  25 – 50kPa                                   Can be moulded by strong finger pressure.
              Stiff                50 – 100kPa                             Cannot be moulded by fingers, can be indented by thumb.
            Very stiff             100 – 200kPa                                        Can be indented by thumb nail.
              Hard                   > 200kPa                                   Can be indented with difficulty by thumb nail.

        DENSITY TERMS – NON COHESIVE SOILS

                           Density                               Density                                                    CPT Cone
                                                                                           SPT “N”
                             Term                                 Index                                                    Resistance
                          Very loose                              < 15%                      0–5                            0 – 2MPa
                            Loose                               15 – 35%                     5 – 10                         2 – 5MPa
                         Medium dense                           35 – 65%                    10 – 30                         5 – 15MPa
                            Dense                               65 – 85%                    30 – 50                        15 – 25MPa
                          Very dense                              > 85%                       > 50                           > 25MPa

        COLOUR

        The colour of a soil will generally be described in a „moist‟ condition using simple colour terms (eg. black, grey, red, brown etc.) modified
        as necessary by “pale”, “dark”, “light” or “mottled”. Borderline colours will be described as a combination of colours (eg. grey-brown).

        EXAMPLE

        e.g. CLAYEY SAND (SC) – medium dense, grey-brown, fine to medium grained with silt.

        Indicates a medium dense, grey-brown, fine to medium grained clayey sand with silt.




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