FEATURE
Table 11: SUMMARY OF PHASE IV SIMPLIFIED PREDICTIONS FOR BOTH
LOAD TEST AND DYNAMIC TEST PILES
Pile No. Pier No. Average Prediction+ Load Test Result+ Figure No.
74 7L 387 390 9
72 5R 276 270 14
65 5R 260 - 20
83 5R 280 - 20
52 6R 282 260 22
59 6R 320 - 25
60 6R 330 - 25
44 6R 350 - 25
43 6R 325 - 25
62 4R 300 390 27
53 4R 175* - 30
73 4R 200* - 30
71 4R 250* - 30
63 1L 279 286 32
42 7R 350 - 36
40 7R 360 - 36
39 7R 340 - 36
62 7R 300 - 37
64 7R 300 - 37
67 1R 300 - 38
30 1L 300 - 39
26 1L 280 - 39
49 1L 290 - 40
42 1L 310 - 40
Figure 2. An excerpt from the Original I-480 report comparing static load
test results to dynamic
Beginning in the late 1960s, use of high strain dynamic testing
has allowed an accurate means of assessing capacity in real time
and in doing so has allowed the driven pile industry to deliver efficient
foundations. One early project using dynamic testing was the
Valley View Bridge in Cleveland, Ohio, conducted between 1970
and 1971. This project, under sponsorship of the Ohio Department
of Transportation and the Federal Highway Administration,
included static load testing and dynamic testing performed over
eight substructures. Results from the test program showed very
good correlation between dynamic test results and static load test
results (Figure 2) and was a significant early project in the acceptance
of dynamic testing as a sole means of capacity assessment.
Fast forward nearly 50 years later and dynamic testing is almost
synonymous with pile driving. Extended correlation studies have
shown a good reliability in capacity prediction. Load and resistance
factor design (LRFD) assigns resistance factors based on the
methods of field capacity assessment. More accurate methods are
assigned higher resistance factors, which result in more economical
foundations. Generally, the cost savings for static or dynamic
testing far exceeds the cost of the testing itself. But the largest savings
comes from preconstruction test programs where the foundation
can be optimized.
Bringing the topic full circle, the same Valley View Bridge is now
nearing completion of building a third bridge between the existing
structures. A preconstruction program was performed using both
static load testing and dynamic testing to optimize foundation
lengths for every substructure. Results from the preconstruction
test program were astonishing. Had results used only end-ofdrive
results for capacity, the project would have required roughly
170,000 lineal feet of piling but because of the testing assessing
setup potential across the entire project, only 64,000 lineal feet of
piling was required.
Figure 1. High strain dynamic testing performed at the Valley View
bridge c.1971
58 | ISSUE 4 2020 www.piledrivers.org