Pile Design and Construction Practice, Fifth edition

following expressions:

(11.1)

(11.2)

where P 3 and P 2 are the loads reaching the pile at the level of the toe of the rod considered,
Ais the cross-sectional area of the pile shaft, Eis the elastic modulus of the material forming
the pile,  3 and  2 are the elastic shortenings of the pile between the pile head and rod 3,
and the pile head and rod 2, respectively, l 3 and l 2 are the lengths of the rods, and Pis the
load on the pile head.
The load at the toe of rod 1 is obtained in a similar manner.
Where the rod strain gauges are used in the interior of a steel tubular pile filled with con-
crete the elastic shortening between each length of pile is that due to the elastic modulus of
the composite section. Thus

(11.3)

where lis the elastic shortening over length l, Pis the load on length l, Asis the area of
steel, Acis the area of concrete, Esis the elastic modulus of the steel, and Ecis the elastic
modulus of the concrete.
While these forms of instrumentation are used mainly for research-type investigations
they can be adopted for the preliminary test piling to give useful design information at a
relatively small additional cost.
Further guidance on the procedure for pile load testing is given by Weltman(11.23).
Dynamic load testsand high strain integrity testing have developed from the need to deter-
mine the static load capacity of driven piles (designed using empirical dynamic formulae as
Section 7.3) at the time of driving. The analyses provide the soil resistance mobilized at the time
of test and may therefore not show time-dependent effects of consolidation on settlement, par-
ticularly when working load is near to ultimate pile capacity. EC7 Clause 7.6.2 sets stringent
criteria for the use of dynamic load tests for assessing the compressive resistance of piles:

 an adequate ground investigation has been carried out and
 the method has been calibrated against static load tests on the same type of pile, of

similar length and cross-section and in comparable ground conditions.

If more than one type of dynamic test is performed then cross-checking of results is
mandatory.
The SIMBAT(11.24)technique for bored cast-in-place piles applies a series of blows to the
pile and measures the set at each blow as in the static tests. Extensions of the stress wave
analytical methods are then used, which, under EC7 Clause 7.6.2.6, must also be calibrated
against static load tests. BSEN 1536 requires any rapid loading tests to be correlated with
maintained static load tests in similar ground. Clearly, cast-in-place piles should not be
tested until they have gained sufficient strength.
The Statnamic testdeveloped jointly by the Berminghammer Corporation in Canada and
TNO-IBBC in the Netherlands(11.25)is now widely used. The load is applied to the pile head

l Pl

AsEs



(^1) 
Ac
As

·

Ec

Es

Load on pile at toe of rod 2 P 2

2 AE 2

l 2

P

Load at pile P 3

2 AE 3

l 3

P

Ground investigations, contracts and testing 527