EurOCEAN 2000 - Vlaams Instituut voor de Zee

Figure 2: Radial variation of unconfined Figure 3: Unconfined compression
tests
strength in jet grout bulb on soil-cement cores
Pile Load Tests
Load tests were carried out on 457 mm diameter (18 inch) driven steel pipe piles at the
Dunkirk site. The tests were load controlled with 15 to 20 increments applied with pause
periods of at least 30 minutes between increments. The increment sizes were reduced and
pause phases extended towards the end of the tests. Following this procedure, each load test
took up to 24 hours to perform. Three main test series were performed.
Capacity Increase from Jet Grouting
Compression tests were carried out on two 10 m long piles. One pile had a nominally 3 m
diameter 5 m high soil-cement bulb formed at the tip and the other was an untreated control
pile. The piles were loaded to failure in compression. The compressive pile capacity was
doubled by the GOPAL treatment.
Evolution of Shaft Resistance with Time
There is considerable evidence that pile shaft capacity in sands increases with time (Chow et
al., 1998). To continue this research, tension tests were performed on the GOPAL reaction
piles. Tension tests were made on previously untested piles at 9 and 80 days and 7 months after
installation. Combining this with previous data from the CLAROM study gives a total of 5
tension tests on previously unfailed piles and 5 tension tests on piles which had been
previously tested to failure.
CONCLUSIONS
The following conclusions can be drawn from the GOPAL field programme:
• The feasibility of forming an artificial sandstone soil-cement bulb of up to 3 m diameter at
the base of a driven steel pipe pile has been demonstrated.
• Pile load tests have been performed on a 457 mm (18 inch) pile with a jet grout formed
base and an identical control pile.
622