geotech report · MCU15/0087

Soil Description Explanation Sheet (1 of 2)

DEFINITION:                                                                 DENSITY OF GRANULAR SOILS
In engineering terms soil includes every type of uncemented
                                                                                       TERM                           DENSITY INDEX (%)
or partially cemented inorganic or organic material found in
the ground. In practice, if the material can be remoulded or                         Very loose                            Less than 15
disintegrated by hand in its field condition or in water it is
described as a soil. Other materials are described using rock                          Loose                                  15 - 35
description terms.
                                                                                   Medium Dense                               35 - 65
CLASSIFICATION SYMBOL & SOIL NAME
                                                                                       Dense                                  65 - 85
Soils are described in accordance with the Unified Soil
Classification (UCS) as shown in the table on Sheet 2.                              Very Dense                            Greater than 85


PARTICLE SIZE DESCRIPTIVE TERMS
       NAME         SUBDIVISION                      SIZE
                                                                            MINOR COMPONENTS
      Boulders                                     >200 mm
                                                                            TERM                 ASSESSMENT                   PROPORTION OF
      Cobbles                                 63 mm to 200 mm                                       GUIDE                  MINOR COMPONENT IN:

       Gravel            coarse                20 mm to 63 mm               Trace of        Presence just detectable         Coarse grained soils:
                                                                                            by feel or eye, but soil         <5%
                         medium                6 mm to 20 mm                                properties little or no
                                                                                            different to general             Fine grained soils:
                            fine              2.36 mm to 6 mm                               properties of primary            <15%
                                                                                            component.
         Sand            coarse              600 μm to 2.36 mm
                                                                            With some Presence easily detected               Coarse grained soils:
                         medium               200 μm to 600 μm                              by feel or eye, soil             5 - 12%
                                                                                            properties little different      Fine grained soils:
                            fine               75 μm to 200 μm                              to general properties of         15 - 30%
                                                                                            primary component.



MOISTURE CONDITION                                                          SOIL STRUCTURE
Dry        Looks and feels dry. Cohesive and cemented soils                            ZONING                              CEMENTING
           are hard, friable or powdery. Uncemented granular
           soils run freely through hands.                                  Layers     Continuous across Weakly                Easily broken up by
                                                                                       exposure or sample. cemented            hand in air or water.
Moist      Soil feels cool and darkened in colour. Cohesive
           soils can be moulded. Granular soils tend to cohere.             Lenses Discontinuous                Moderately Effort is required to
                                                                                   layers of lenticular         cemented break up the soil by
Wet        As for moist but with free water forming on hands                       shape.                                  hand in air or water.
           when handled.
                                                                            Pockets Irregular inclusions
                                                                                    of different material.

CONSISTENCY OF COHESIVE SOILS
                UNDRAINED                                                   GEOLOGICAL ORIGIN
 TERM           STRENGTH                       FIELD GUIDE
                 su (kPa)                                                   WEATHERED IN PLACE SOILS
                                                                            Extremely  Structure and fabric of parent rock visible.
 Very Soft         <12             A finger can be pushed well into the     weathered
                                   soil with little effort.                 material
 Soft             12 - 25          A finger can be pushed into the soil
                                                                            Residual soil       Structure and fabric of parent rock not visible.
                                   to about 25mm depth.

 Firm             25 - 50          The soil can be indented about 5mm
                                   with the thumb, but not penetrated.      TRANSPORTED SOILS
                                                                            Aeolian soil Deposited by wind.
 Stiff           50 - 100          The surface of the soil can be
                                   indented with the thumb, but not         Alluvial soil       Deposited by streams and rivers.
                                   penetrated.
                                                                            Colluvial soil      Deposited on slopes (transported downslope
 Very Stiff      100 - 200         The surface of the soil can be marked,                       by gravity).
                                   but not indented with thumb pressure.
                                                                            Fill                Man made deposit. Fill may be significantly
 Hard             >200             The surface of the soil can be marked                        more variable between tested locations than
                                   only with the thumbnail.                                     naturally occurring soils.

 Friable            –              Crumbles or powders when scraped         Lacustrine soil Deposited by lakes.
                                   by thumbnail.
                                                                            Marine soil         Deposited in ocean basins, bays, beaches
                                                                                                and estuaries.