Development Application Part 2 of 2 - Geotech Report and Plans - OPW13/0816

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 The test is carried out in a borehole by driving a 50mm                                    resistance, fs, in kPa). These forces are measured by
 diameter split sample tube with a tapered shoe, under                                      electrical transducers (strain gQ~g~:::; ’..::~~::-: ~~: :::-::

 the impact of a 63 kg hammer with a free fall 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                                               .                          Friction Resistan eels (kPa)x 100
                                                                                            Fnct’
                                                                                                Ion R at’
                                                                                                        /0 (FR)         _

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                                                                                                                           cone resistan ce, qe (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                                      N = 13                              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             to   100    MPa    for
                                                                                                          up                             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 (USO)in clays.                               In           are required.

such circumstances, it is noted on the borehole logs.                                       The               resistance value                    continuous
                                                                                                     cone                          provides   a

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 600 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   "Ne" 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, qe, 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 RELA TING TO THIS REPORT JUNE 2009.LWP
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                                                                                                                     SOIL SURVEYS ENGINEERING