using cohesive backfill for

[AK92]

Hi all,

For some reason, the client is unwilling to use cohesionless backfill for a temporary reinforced earth wall (using wraparounds) for the edge of an embankment fill. So far, they are proposing the use of MH type soils. I'm concerned about the problems that using cohesive fill might cause as they are generally not recommended for reinforced earth applications. Are there any design manuals to cope with designing reinforced earth walls with cohesive backfill?

The general ideas I'm thinking of is using a combination of
1) placing the fill wet of optimum, then allowing for the consolidation settlements
2) using nonwoven geotextiles (for drainage and dissipation of excess pore pressures to improve bond strength and reduce water pressure) and geogrids (to provide the tensile strength).

I'm not too concerned about the deformation as it is for a temporary fill. The ground beneath the embankment would be laced by wick drains allowing the whole fill to settle, and then the surcharge fill would be taken off. The reason why the temporary reinforced earth wall has to be there is due to a lack of space. So in essence, the temporary reinforced earth wall would have to be designed to settle along with the ground.

 

[oldestguy]

Is the lack of space due to a property line? Perhaps a building there? While you may be legally off the hook, remember that that nearby ground also will be affected. The main reason for problems that I have dealt with is adding weight next to a building or a site.

 

[AK92]

@oldestguy

The lack of space is due to a public road which is next to the site. However, this embankment is going to be offset some distance away from the public road, with the rest of the permanent embankment being constructed at a later stage, supported by settlement reducing piles.

We haven't looked into the effect of the embankment construction onto the public road. With undrained behavior probably I will expect heaving and significant lateral displacements, however as I have wick drains installed, probably the settlement trough will tend to cancel the heave out (just a guess at it, not too sure how to make a good estimate)

My concern is with the temporary retaining wall, as it has to be constructed with cohesive backfill. Obviously, the placement moisture content is going to be an issue (especially in severe tropical weather).

Also, the properties of the clay is an issue. How would I know beforehand what is a good estimate of the phi angle, and can I assume drained behavior if I have nonwoven geotextiles and geogrids working together.