Pile Design and Construction Practice, Fifth edition

522 Ground investigations, contracts and pile testing

With regard to loading procedures, EC7 Clause 7.5.2.1 only refers in a note to the
recommended procedure ‘Axial Pile Loading Test, Suggested Method’as published in the ASTM
Geotechnical Testing Journal, June 1985, pp. 79–90. This is generally followed in current
European practice. However, ISSMGE has produced a recommendation document(11.19)for the
execution and interpretation of axial static pile load tests which is consistent with EC7 philos-
ophy and is likely to form the basis of a new European standard. A note in Clause 7.5.3
refers to the procedures for dynamic tests in ASTM Designation D4945, ‘Standard Test
Method for High-Strain Dynamic Testing of Piles’.
The ASTM axial load procedure can be used for a test to twice the working load. If it is
desired to obtain the ultimate load on a preliminary test pile it is useful to adopt the ML
method for up to twice the working load, and then to continue loading to failure at a constant
rate of penetration. A further modification of the ML test consists of returning the load to
zero after each increment. This form of test is necessary if the net settlement curve is used
as the basis of defining the failure load (see Section 11.4.2). It is essential to maintain a
constant rate of load application as specified in EC7. It has been found that the slower the
rate the smaller is the ultimate failure load. Hence the need for standardization both for ML
and CRP testing.
CRP and ML tests use the same type of loading arrangements and pile preparation.
A square cap is cast onto the head of a concrete pile with its underside clear of the ground
surface. Steel piles are trimmed square to their axis and a steel plate is welded to the head,
stiffened as necessary by gussets. Suitable loading arrangements for applying the load to the
pile by a hydraulic jack using as the reaction either kentledge, tension piles or cable anchors
are shown in Figures 11.7, 11.8 and 11.9 respectively. The clearances between the pile and
the reaction support systems are noted in each case. These are necessary to avoid the
induced horizontal pressures from the supports having an appreciable effect on the shaft
friction and base load of the test pile. It is uneconomical to space the supports so widely
apart that all effects are eliminated, and if necessary the contribution of these surcharge
effects should be calculated and allowed for in the interpretation of the test results.

Kentledge blocks

Timber spacers

Angle lacing and

tie bolt

Stiffeners Universal

beams

Load cell

Dial gauge

1.3 m minimum

Clear space

Cap cast on to

head of test pile

Hydraulic jack Timber

crib

Test pile

Supports

for four dial

gauges

Bracing

Clamp

U.B.

Universal beams

Figure 11.7Testing rig for compressive test on pile using kentledge for reaction.