Geotch Report December 2021 95141.00.R.001.RevA

Cohesive Soils                                                 Estuarine soil – deposited in coastal estuaries;
Cohesive soils, such as clays, are classified on the           Marine soil       –   deposited     in   a    marine
basis of undrained shear strength. The strength                 environment;
may be measured by laboratory testing, or                      Lacustrine soil – deposited in freshwater
estimated by field tests or engineering                         lakes;
examination. The strength terms are defined as
follows:                                                       Aeolian soil – carried and deposited by wind;
                                                               Colluvial soil – soil and rock                  debris
                                         Undrained              transported down slopes by gravity;
    Description        Abbreviation
                                       shear strength          Topsoil – mantle of surface soil, often with
                                           (kPa)                high levels of organic material.
    Very soft              VS               <12
                                                               Fill – any material which has been moved by
    Soft                    S              12 - 25              man.
    Firm                    F              25 - 50
    Stiff                   St            50 - 100
    Very stiff             VSt            100 - 200        Moisture Condition – Coarse Grained Soils
    Hard                    H               >200           For coarse grained soils the moisture condition
    Friable                 Fr                -            should be described by appearance and feel using
                                                           the following terms:
                                                              Dry (D)         Non-cohesive and free-running.
Cohesionless Soils                                            Moist (M)       Soil feels cool, darkened in
Cohesionless soils, such as clean sands, are                                   colour.
classified on the basis of relative density, generally                         Soil tends to stick together.
from the results of standard penetration tests                                 Sand forms weak ball but breaks
(SPT), cone penetration tests (CPT) or dynamic
                                                                               easily.
penetrometers (PSP). The relative density terms
are given below:                                              Wet (W)         Soil feels cool, darkened in
                                                                               colour.
    Relative          Abbreviation     Density Index                           Soil tends to stick together, free
    Density                                (%)                                 water forms when handling.
    Very loose             VL              <15
    Loose                   L             15-35
    Medium dense           MD              35-65           Moisture Condition – Fine Grained Soils
    Dense                   D              65-85           For fine grained soils the assessment of moisture
                                                           content is relative to their plastic limit or liquid limit,
    Very dense             VD               >85            as follows:
                                                              ‘Moist, dry of plastic limit’ or ‘w <PL’ (i.e. hard
                                                                and friable or powdery).
Soil Origin
                                                              ‘Moist, near plastic limit’ or ‘w ≈ PL (i.e. soil can
It is often difficult to accurately determine the origin
                                                                be moulded at moisture content approximately
of a soil. Soils can generally be classified as:
                                                                equal to the plastic limit).
      Residual soil - derived from in-situ weathering
                                                              ‘Moist, wet of plastic limit’ or ‘w >PL’ (i.e. soils
       of the underlying rock;
                                                                usually weakened and free water forms on the
      Extremely weathered material – formed from               hands when handling).
       in-situ weathering of geological formations.
                                                              ‘Wet’ or ‘w ≈LL’ (i.e. near the liquid limit).
       Has soil strength but retains the structure or
       fabric of the parent rock;                             ‘Wet’ or ‘w >LL’ (i.e. wet of the liquid limit).
      Alluvial soil – deposited by streams and rivers;




                                                                                                             May 2019