EurOCEAN 2000 - Vlaams Instituut voor de Zee

Solution
One solution to this problem would be to have stronger soils below the pile tip. Onshore, jet
grouting is a proven soil improvement technique that is used to mitigate difficult foundation
conditions. The main objective of this project is to investigate the potential of using this
process to create a strong durable bulb of soil-cement below the pile tip, increasing end bearing
and allowing a reduction in pile length.
The first step to develop this technology is to prove that it is possible to create a soil-cement
bulb below the pile tip and importantly, to measure the increase in pile capacity. Grouting trials
and load tests are being carried out on 457 mm (18 inch) diameter steel piles at a site in
northern France. This paper discusses the jet grouting technique and field testing, and gives
preliminary indications of five capacity increase.
Test Site
The field test site is located at Dunkirk on the northern coast of France on land made available
thanks to the PORT AUTONOME DU DUNKERQUE authority. The area has been used for
other pile load research in the past by the CLAROM group (Brucy et al., 1991) and previous
tests by Imperial College (Chow, 1997).
JET GROUTING
Jet Grouting Method
Jet grouting is a ground improvement technique used to create an in-situ mass of grouted soil.
The drillstring is advanced to the bottom of the grouting zone by rotary drilling. When the
target depth is reached, a high pressure jet of cement grout is ejected horizontally from the
drillstring. The jet cuts through the in-situ material, leaving behind a mixture of grout and soil.
The drillstring is rotated and slowly lifted to form a soil-cement column. As the grout sets up,
the material cures into a solid mass.
Double-fluid (grout and air) jet grouting was used. This system uses a concentric double tube
drillstring carrying separate streams of high pressure grout and compressed air to the grouting
head. At the ejection nozzle the horizontal grout jet is protected by a compressed air shroud to
increase cutting energy, providing large column diameters.
619