Pile loading testsusing procedures described in Section 11.4.2 can be used directly to
obtain design resistance values or to verify design resistances derived from empirical or
analytical methods. If there is any doubt about the validity of such methods loading tests are
required to be made on trial piles. The Geotechnical Risk Category, as previously described,
should be considered when deciding on the programme for pile loading tests. At this stage
the trial piles can also be used to check that the proposed installation method can achieve
the design penetration depth without difficulty (particularly in the case of driven piles) and
can produce a soundly constructed foundation. Loading tests are made on working piles at
the project construction stage to confirm the experiences of pre-contract trials and as a
routine check on the contractor’s workmanship.
Whenever possible static pile loading tests should be taken to failure or to the stage where
a failure can be reliably extrapolated from the load/settlement diagram. In cases where the
failure load or ultimate limit state resistance Rcmcannot be interpreted from a continuously
curving load/settlement diagram, Clause 7.6.1.1(3) of EC7 permits Rcmto be defined as the
load applied to the pile head which causes a settlement of 10% of the pile diameter.
Clause 7.5.2.1 recommends that tension tests should always be taken to failure because of
doubts about the validity of extrapolation in uplift loading.
The correlation factors shown in Table 4.7 are applied to ultimate resistances (Rcm)
obtained from loading tests on trial or working piles to obtain characteristic resistances Rck.
The partial factors in Tables 4.3 to 4.5 are then applied to arrive at the design resistances Rcd.
When instrumented piles are used to measure the separate components of base and shaft
resistances (Rbkand Rsk) the appropriate partial factors are used as shown in the tables. If the
structure above the piles is stiff enough to redistribute loads from weaker to stronger piles
the correlation factors may be reduced by the factor of 1.1 as noted above for calculations
using analytical methods, provided that is never less than 1.0.
Clause 7.5.3. of EC7 states that dynamic loading testsmay be used to estimate resistances
to axial compression loads provided that there has been an adequate ground investigation
and that the method has been calibrated against static loading tests on the same type of pile
and of similar length and cross-section, and in comparable soil conditions. The equipment
used for dynamic testing and the method of interpretation are described in Section 7.3.
At the stage of trial piling the correlation factors shown in Table 4.8 are applied to the test
results to obtain characteristic and design resistances in the manner described above for static
load tests. Table A.11 in Annex A of EC7 should be consulted for the various qualifications in
the application of the correlation factors which depend on the instrumentation used in the tests.
1
150 Resistance of piles to compressive loads
Table 4.7Correlation factors ( ) to derive characteristic
values from static pile load tests
n
1234 5
1.40 1.30 1.20 1.10 1.00
1.40 1.20 1.05 1.00 1.00Notes
n denotes the number of tested piles.
denotes on the mean values of measured resistances in static
tests.
denotes on the minimum values of measured resistances in static
load tests. 2 1 2 1