Ground Improvement (rigid inclusions)

[Jhin]

I'm looking for standards and good references to use for analysing rigid inclusions (e.g. CMC's, stone columns, piles, etc) to reduce consolidation settlements in soft clay after placement of fill + other surcharge loads. More specifically, I'm interested in calculating the average modulus between soil and structure (another method rather than obtaining a weighted average?) and designing the bridging platform at the top of these rigid inclusions.

 

[BigHarvey]

You can refer to the following book in English :

http://www.presses-des-ponts.fr/not...h-under-the-title-asiri-national-project.html

It is the result of a national research project in France called ASIRI.

 

[geomane]

I usually consult with Hayward Baker when dealing with ground improvement. You could contact them and see if they could help.

 

[Okiryu]

Look at:

http://www.geotechtools.org/

This website has very good info for all kind of soil improvement techniques.

The FHWA manuals also have information about different type of soil improvements.

 

[Jhin]

Thank you so much! Would you also know if any of the BS or EN specifically point to rigid inclusions and bridging platforms? Thanks!

 

[ATSE]

The term rigid inclusion is a relatively new term in the ground improvement world and can mean a couple of different things, depending on which design-build contractor you speak with. You should clarify if the rigid inclusion is formed thru displacement - similar to a drill displacement pile - or thru replacement - similar to continuous flight augering ("CFA").
Grout strength can vary from 1,000psi to 4,0000psi.
Will there be a load transfer platform above the top of the inclusions?
For comparing stiffness, keep in mind that short term stiffness ratio will be different than long term stiffness ratio. Over time, the Rigid Inclusion will attract more load.
Will the rigid inclusion be reinforced with steel rebar? If not, you will have a very stiff axial element with little or no flexural stiffness, which will limit the applicability for any installation with lateral loads or lateral strain.

 

[Okiryu]

I agree with ATSE. These inclusions have large stiffness and may be considered as piles. I remembered that some research for stone columns showed load transfer curves same as curves for piles. So these inclusions attract more load, this also depends on their spacing. I was also taking with engineers here in Japan and they suggested to consider soil-cement columns as piles due to they higher stiffness. In fact, soil-cement columns are checked for lateral resistance based on the compressive strength of the soil-cement slurry.

 

[Jhin]

ATSE/Okiryu, Our options still range between rigid and semi-rigid inclusions due to ground conditions (riverbank mud and recent very soft to soft clays ~4-8m thk over moderately dipped rock head), site constraints (eg old buried structures where we have to work around with) and construction staging (has to be implemented in stages because of traffic in a very narrow corridor). We are likely to have load transfer platforms as the embankment thickness is only between 1-3m and there we will be unbalanced loading (potential lateral spreading towards the river).

 

[BigHarvey]

The choice between rigid and semi-rigid inclusions (ie stone columns) will depend on the following parameters : depth of treatment, intensity of load and mechanical properties of soil (mainly cohesion)
If the depth of treatment is greater than 15m or load greater than 5 tons/m2 go for rigid inclusions.
If the cohesion is lower than 15 KPa use precast rigit inclusion, stone columns or cast in place concrete inclusions won't make it (impossible to compact the stone due to lack of lateral resistance from soil and the weight of fresh concrete will be too much for the surrounding ground and caus large concrete overbreak leading to question inclusion integrity).