Jet Grouting

[Zambo]

We propose to use jet grout columns to create a foundation to support a relatively small rock breakwater. The columns will be constructed approx 20m into the seabed (depth of water averaging 10m). Has anyone any experience on this type of project, one concern is environmental issues from escape of the binder at the seabed. Our contractor intends first to jack in a casing to about 3m below the seabed then install the jet grout equipment within the casing, pumps will take the excess material from the casing back to the barge.

 

[BigHarvey]

It should work but the quantity of spoil to handle will be close to the volume of the columns. This should prove difficult to do given the limited space available on a barge.
Since a breakwater allows significant settlement, why don't you rigid inclusions ( in this case they could be steel deiven piles , H or tubular )to limit the settlements.

 

[Zambo]

BigHarvey thanks for the response. The situation is a bit more complicated than I described, we have some structure on the rock bund.

My main concern is contamination. I just read on the internet that anti-washout admixtures are one possibility. The sizing of the casing and the pumps may be another point.

One more interesting item for me to investigate is the different techniques of grout injection only, air+grout and air+grout+water

 

[BigHarvey]

You can limit the settlements as much as you want with rigid inclusions ( say 1 inch for example ).

if you go for jet grouting , you must use a jack-up because you pilot the nozzle by steps of a few centimeters. ( spuds won't allow you such an accuracy, particularly if yo are not in a sheltered area ).

Anti- washout admixtures work well for concrete placed under water but I never heard of any application for jet grouting.

Double jet is what works the best at the present time ( air plus grout ).

As I said the major problem is to handle the large volume of spoil generated by the process ( 80 to 100% ). Zero contamination can be obtained but there is a cost in front of it !

 

[DRC1]

This seems like a fairly complicated operation. Would precast piles driven with a follower be an option?