Changes Application - MCU15/0023.02

                                                                - 3-

The test is carried out in a borehole by driving a 50mm                resistance, f" in kPa). These forces are measured by
diameter split sample tube with a tapered shoe, under                  electrical transducers (strain gauges) within the cone
the impact of a 63 kg hammer with a free fail of 760                   device. The ratio between friction resistance and cone
mm.    It is normal for the tube to be driven in three                 resistance is also calculated as a percentage, ie.-
successive 150 mm increments and the 'N' value is                          . f'  R (' (FR) _ Friction Resistancel, (kPa) x 100
                                                                       F (Ie IOn a 10          -      cone resislan ce, qc (kPa)

taken as the number of blows for the last 300 mm, the                  The friction ratio, FR, is generally low in sands (less
upper 150 mm being neglected due to possible                           than 1% or 2%) and generally higher in clays (say 3%
disturbance from the drilling method. In dense sands,                  or more).        The interpretation of sandy clays, clayey
very hard clays or weak rock, the full 450 mm                          sands and material with a high silt content is more
penetration may not be practicable and the test is                     difficult, but intermediate values (between 1% and 3%)
discontinued at a reduced penetration.                                 would be expected.            Highly organic clays and peats
In the case where full penetration is obtained with                    generally have a friction ratio in excess of 5%.
successive blow counts for each 150 mm of, say 4, 6                    Static cone data is recorded in the field on disc for later
and 7 blows, the record shows,                                         presentation using computer aided drafting.
         4,6,7                                                         The equipment can be operated from any conventional
In a case where the test is discontinued short of full                 drill rig. A total applied load in the range of 4 to 10
penetration, say after 15 blows for the first 150 mm                   tonnes is required for practical purposes, although
and 30 blows for the next 40 mm, the record shows:                     lighter loads may be used. The cone penetrometers
          15,30/40mm                                                   are available with various capacities of cone resistance
The results of the test can be related empirically to the              ranging     up     to   100     MPa    for   general   purpose
engineering properties of the soil.                                    investigations, while a range of 0 to 10 MPa can be
Occasionally, the drop hammer is used to drive 50mm                    used where more sensitive investigations of soft clay

diameter thin walled sample tubes (U50) in clays. In                   are required.
such circumstances, it is noted on the borehole logs.                  The    cone      resistance    value   provides a continuous

A modification to the SPT test is where the same                       measure of soil strength or density, and together with
driving system is used with a solid 60° tipped steel                   the friction ratio, provide very useful indications of the
cone of the same diameter as the SPT hollow sampler.                   presence of narrow bands of geotechnically significant
The solid cone can be continuously driven for some                     layers such as thin, soft clay layers or lenses of sand
distance in soft clays or loose sands, or may be used                  which might otherwise be missed using conventional
where damage would otherwise occur to the SPT. The                     drilling methods.
results of this Solid SPT are shown as "N," on the                     The lithology of the encountered soils is interpreted
borehole logs, together with the number of blows per                   from static cone data and is generally presented on the
150 mm penetration.                                                    static cone log sheets.
Cone     Penetration       Tests      - Test Method - Cone             It is important to note that the lithology is interpreted
Penetration Tests (CPT) are carried out in accordance                  information and is based on research by Schmertmann
with AS 1289 Test 6.5.1-1977, using an electrical                      (1970), Sanglerat (1972), Robinson and Campinalli
friction-cone penetrometer.                                            (1986), modified to suit local conditions as indicated by
The test essentially comprises the measurement of                      borehole information and laboratory testing.
resistance to penetration of a cone of 35.7 mm                         As soils generally change gradually it is sometimes
diameter pushed into the soil at a rate of 10-20 mm per                difficult   to    accurately    describe     depths of   strata
second     by hydraulic force.                 The resistance   to     changes, although greater accuracy is obtained with
penetration is recorded in terms of pressure on the end                the static cone compared with conventional drilling. In
area of the cone (cone resistance, q" in MPa) and                      addition, friction ratios decrease in accuracy with low
friction on the side of the 135 mm long sleeve                         cone resistance values, and in desiccated soils. As a
immediately above the top of the cone (friction                        result, some overlap and minor discrepancies may


NOTES RELATING   TO THJS REPORT.   JUNE 2009                                                   SOIL SURVEYS ENGINEERING