Attachment B - Geotechnical Analysis

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Interpretation of the
Subsurface Sheets
                                                            Very Low Strength (VLS)                  < 2 MPa (UCS)
The terminology included on Arcos Unit Group Pty
                                                            Low Strength (LS)                        2 to 6 MPa (UCS)
Ltd’s has been evolved from AS1726:2016. Typically
                                                            Medium Strength (MS)                     6 to 20 MPa (UCS)
a soil’s strength, colour, plasticity, grain size, other
                                                            High Strength (HS)                       20 to 60 MPa (UCS)
inclusions, and moisture will be described. A rock’s
                                                            Very High Strength (VHS)                 60 to 200 MPa (UCS)
strength, weathering, colour, grain, and other
                                                            Extremely High Strength (EHS)            > 200 MPa (UCS)
inclusions are typically described.

Soil                                                        Very Low Strength (VLS)                  < 0.1 Is(50)
                                                            Low Strength (LS)                        0.1 to 0.3 Is(50)
Soil is typically described by the components that          Medium Strength (MS)                     0.30 to 1.0 Is(50)
make it up by percentage or whichever has a                 High Strength (HS)                       1.0 to 3.0 Is(50)
governing behaviour. The types and sizes                    Very High Strength (VHS)                 3.0 to 10.0 Is(50)
reproduced from AS1726 are:                                 Extremely High Strength (EHS)            > 10.0 Is(50)
 Boulder                 >200 mm
 Cobble                  63 to 200 mm                      The Is(50) values are based on a correlation
 Gravel                  2.36 to 63 mm                     between the unconfined compressive strength
 Sand                    0.075 to 2.36 mm                  (UCS) of 20. This value varies significantly and site
 Silty                   0.002 to 0.075 mm                 specific testing must take precedence.
 Clay                    < 0.002 mm
                                                           Rock weathering is broken down as follows:
The strength of soil is usually assessed by suitably
experienced persons through the use of laboratory           Extremely weathered       Behaves as soil but rock
test results, published literature, field assessments or    (EW)                      structure evident
a combination of the above. The strength of soil is         Highly weathered          Colour and strength of original
characterised into either cohesive (clays and silts) or     (HW)                      fresh rock is not recognisable.
cohesionless (sands and gravels) as shown below:                                      Decomposition of rock evident
                                                            Moderately                Defects are heavily stained with
 Cohessive Soil           Strength Term                     weathered (MW)            rock mass showing signs of
 Very Soft                < 12.5 kPa                                                  discolouration
 Soft                     12.5 to 25 kPa                    Slightly weathered        Some staining but minimal to no
 Firm                     25 to 50 kPa                      (SW)                      change in strength
 Stiff                    50 to 100 kPa                     Fresh stained             Minor staining evident
 Very Stiff               100 to 200 kPa                    (FS)
 Hard                     > 200 kPa                         Fresh rock                No change
                                                            (FR)
 Cohesionless Soils       Strength Term (uncorrected Qc)
 Very Loose               <2 MPa                           Rock fracturing is broken down as follows and can
 Loose                    2 to 5 MPa                       only be accurately described where undamaged
 Medium Dense             5 to 15 MPa                      continuous sampling has been undertaken:
 Dense                    15 to 25 MPa
 Very Dense               > 25 MPa                          Fragmented (Fg)             Defect spacings < 20 mm
                                                            Highly Fractured (HF)       Defect spacings 20 to 50 mm
Rock                                                        Fractured (Fr)              Defect spacings 50 to 200 mm
                                                            Slightly Fractured (SF)     Defect spacings 200 to 1000 mm
Rock is typically described by the components that          Unbroken (Ub)               Defect spacings > 1000 mm
make it up by percentage or whichever has a
governing behaviour. The strength of rock is typically
the most important component. Typically, the
strength of rock is based on laboratory testing, tactile
assessment and other observations as relevant. The
industry standard method for assessing the strength
of rock in the field is to use the point load strength
index (AS4133.4.1). It is important to note that the
point load strength index does not take into
consideration the degree of fracturing of a rock mass
which can both lower and increase the overall rock
strength. The strength of rock is broken down as
follows: