Ground investigations, contracts and testing 531the test pile. The desirable maximum load for repeated application cannot be readily deter-
mined in advance of the load testing programme since the relationship between the ultimate
load for a single application and that for repeated application is not known. Ideally a single
pile should be subjected to a CRU test to obtain the ultimate load for a single application.
Then two further piles should be tested; one cycled at an uplift load of, say, 50% of the
single-application ultimate load, and the second at 75% of this value. At least 25 load
repetitions should be applied. If the uplift continues to increase at an increasing rate after
each repetition, the cycling should be continued without increasing the load until failure in
uplift occurs. Alternatively, an incremental uplift test can be made with say 10 repetitions of
the load at each increment.
A typical load/time/uplift curve for an ML test is shown in Figure 11.15. The criteria for
evaluating the failure load are similar to those described in Section 11.4.2.
EC7, Clause 7.6.3.2, prescribes a method of deriving the design tensile capacity, Rtd, of a
single pile from tension tests as described in Section 6.2.2.
A loading rig for an uplift test is shown by Figure 11.16. This utilizes the same compo-
nents as the compressive load testing rig shown in Figure 11.8. The methods used for
measuring the jacking force and the movement of the pile head are the same as those used
for compressive tests. It is particularly important to space the ground beams or bearers at an
Figure 11.14Analysis of load/settlement curves from pile loading test (after Chin(11.26)) (a) End-bearing
pile (b) Friction and end-bearing pile (c) Broken pile.
Settlement/load Settlement/load/p×^103Ultimate base resistance
14.314.3(^55) 0.0175 820 kN
Settlement
^
(mm)
Settlement
^
(mm)
0
(a)
(c)
(b)
0
4 2.5
8
12
16
20
Settlement
^
(mm)
0
2
1.3
Ultimate shaft friction
Total pile resistance
2.2 4.2
5.0
5.6
4
6
8
10
0246810
0
4
8
12
16
20
4 8 12 16 20 0 1 2 3 4 5 6
/p× 103
Settlement/load/p×^103
10
0.0034
55 2 940 kN
5
0.0029
55 1 720 kN