CEMP-E
EI 02G001
01 July 1997
settlement is consistent with the calculated settlement for offshore piles near the head wall. Analysis of the
elastic characteristics of the piles showed that the shaft friction is significant and appears to provide much of
the bearing capacity for piles near the headwall.
d. Discussion of Results. Based on the results of the SPT tests and past experience, the foundation
of the drydock should have had adequate capacity both onshore and offshore. The driving of the piles
started onshore and proceeded to the offshore end of the drydock. As this took place, the penetration
resistance during actual driving decreased. Additionally, penetration resistance decreased within each
group as new piles were driving within a group. These events in the driving of the offshore piles cast doubt
on the bearing capacity of the offshore piles. The probable cause of the decrease in driving resistance was
the buildup of excess pore water pressures in the construction area coupled with the effects of
preconstruction blasting, which may have further reduced cementation between sand particles near
group N-5 and N-6. Although the presence of these factors was certain, because of them it was impossible
to quantify the bearing capacity of the offshore piles without further verification.
5-3. SUPPLEMENTAL TEST PROGRAM. As a consequence of the results of the installation of the
offshore piles, a supplemental test program was performed from 24 February to 5 March 1992, about
7 months after installation of the production piles.
a. Repeated Static Load Test. To verify the load bearing capacity of the offshore piles, additional load
tests were performed on selected piles. One repeated static load tests was performed on Pile S-5-12. The
purpose of this test was to calibrate dynamic monitoring results by the Case method and CAPWAP method
(ASTM D 4945). This was to determine the bearing capacity of the restruck piles, and thus obviate the
need to statically test each of these piles. The static test was repeated with greater maximum loads to
check for the possible breakdown of coral particles and the piles and adhesion between coral particles that
could reduce bearing capacity from repeated loads. Additionally, an indicator pile was driven between
groups S-4 and S-5 after the repeated static load test. Bearing capacity of this indicator pile was evaluated
from the pile driving analyzer and wave equation results. After the dynamic methods were calibrated,
10 restrikes of the production piles were also completed, which included the pile that was load tested.
(1) Procedure. The repeated static compression test was performed on pile S-5-12 in accordance
with ASTM D 1143. The pile was embedded to a depth of 53 feet, and it was tested 261 days after
installation. Figure 5-3b shows the blow count record of this production pile as it was originally driven in
June 1991. The first cycle loaded the pile to the design load of 120 kips, then the load was reduced to
zero. The second cycle was conducted to 240 kips, twice the design load, then returned to zero load. The
third and final cycle was to be conducted to 360 kips, three times the design load. The standard loading
procedure was used for the first and second load cycles, while loading in excess of the standard load option
was used to complete the third cycle.
(2) Results. Figure 5-12 shows the results of the static load tests. For the first cycle, there was
total elastic deformation after return to the zero load. The second cycle caused approximately 0.03 inch
of permanent settlement. Creep recorded during the 12-hour holding period at 240 kips was also 0.03 inch.
The permanent settlement equaled the amount of creep during the holding period. For the third load test,
the hydraulic pump malfunctioned at the 360 kips load and the test could not be completed. The creep rate
observed at this load was approximately 0.016 inch/hour, and total permanent settlement of the pile toe at
this load was approximately 0.2 inch. A plunging failure was not achieved. Wave equation analysis using
the CAPWAP program and the observed blow count of 34 blows/foot (as opposed to the 4 blows/foot
during original driving) determined from the restrike of this pile estimated a failure load of about 440 kips.
Ultimate capacity by the Case method was 298 kips. The CAPWAP method better evaluates the soil input
parameters and distribution of soil resistance from the PDA results, and was expected to lead to a better
estimate of bearing capacity than the Case method.
5-5
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