Att 9 - Geotech and PASS report

Description and Classification Methods
The methods of description and classification of       Definitions of grading terms used are:
soils and rocks used in this report are based on       •      Well graded - a good representation of all
Australian Standard AS 1726-1993, Geotechnical                particle sizes
Site Investigations Code.          In general, the     •      Poorly graded - an excess or deficiency of
descriptions include strength or density, colour,             particular sizes within the specified range
structure, soil or rock type and inclusions.
                                                       •      Uniformly graded - an excess of a particular
                                                              particle size
Soil Types
Soil types are described according to the              •      Gap graded - a deficiency of a particular
predominant particle size, qualified by the grading           particle size with the range
of other particles present:
                                                       Cohesive Soils
 Type                      Particle size (mm)          Cohesive soils, such as clays, are classified on the
 Boulder                          >200                 basis of undrained shear strength. The strength
                                                       may be measured by laboratory testing, or
 Cobble                          63 - 200
                                                       estimated by field tests or engineering
 Gravel                          2.36 - 63             examination. The strength terms are defined as
 Sand                          0.075 - 2.36            follows:
 Silt                          0.002 - 0.075
 Clay                             <0.002                   Description       Abbreviation      Undrained
                                                                                             shear strength
                                                                                                 (kPa)
The sand and gravel sizes can be further
                                                           Very soft               vs             <12
subdivided as follows:
                                                           Soft                    s               12 - 25
 Type                      Particle size (mm)              Firm                    f               25 - 50
 Coarse gravel                   20 - 63                   Stiff                    st            50 - 100
 Medium gravel                    6 - 20                   Very stiff              vst           100 - 200
 Fine gravel                     2.36 - 6                  Hard                    h               >200
 Coarse sand                    0.6 - 2.36
 Medium sand                     0.2 - 0.6             Cohesionless Soils
                                                       Cohesionless soils, such as clean sands, are
 Fine sand                      0.075 - 0.2            classified on the basis of relative density, generally
                                                       from the results of standard penetration tests
The proportions of secondary constituents of soils     (SPT), cone penetration tests (CPT) or dynamic
are described as:                                      penetrometers (PSP). The relative density terms
                                                       are given below:
 Term              Proportion          Example
 And                 Specify       Clay (60%) and          Relative      Abbreviation    SPT N        CPT qc
                                    Sand (40%)             Density                       value         value
                                                                                                      (MPa)
 Adjective          20 - 35%         Sandy Clay
                                                           Very loose         vl            <4          <2
 Slightly           12 - 20%       Slightly Sandy
                                         Clay              Loose              l          4 - 10        2 -5
 With some          5 - 12%        Clay with some          Medium            md          10 - 30      5 - 15
                                        sand               dense
 With a trace of     0 - 5%        Clay with a trace       Dense             d           30 - 50      15 - 25
                                       of sand             Very              vd           >50          >25
                                                           dense




                                                                                                     May 2017