Swellling Pressure on Retaining Walls

[GeoGeoGeo]

How do i take into account the swelling pressure of clay on my retaining wall?

I have 4 meters of active clay but how do I estimate the swelling pressures on this 4m. I have seen some publication in which in for the first 0.5m to 1m the swelling pressure is taken as the Passive Earth Resistence and then the swelling pressure decreases to the at rest pressure until the non active zone.

Any ideas?

Many thanks

 

[MTNClimber]

I always harp on the fact that you should talk to colleagues in your area when it comes to dealing with expansive soils. I have found that each region of the world deals with it differently.

When I worked in Colorado, we typically used equivalent fluid densities of around 50 pcf for active and 65 pcf for at-rest for walls backfilled with clay. We did not specify special loading cases with the clay having a high versus low swell potential.

All the clay soils should have been moisture conditioned to optimum and compacted in lifts as it was installed as backfill material. This significantly reduces or even eliminates the swell potential of the clay while it maintains that moisture. The upper portion of the clay may dry out over time and then rehydrate, potentially adding some swell pressure to the retaining wall, but I haven't seen provisions for dealing with the topic before.

 

[emmgjld]

The problem is not a trivial use of the normal range of equivalent fluid pressure.
The problem is also dependent on the original and the now climate, as a possible result of irrigation.
My experience is on the West Slope in Colorado, but I did break out (45-50 years ago) on the Front Range of Colorado, which has a fair bit different climate.
Has the land use behind the retaining wall changed?
Is the original ground to be retained newly irrigated?
I have had a basement wall push from swelling clays 15 to 20 feet from the wall.
When I am anticipating a problem, I typically recommend fluid pressures of 120 to 300 psf, depending on the particular geologic formations encountered, site geometry/layout, amount of actual backfill utilized (see MTNClimber reply) and future groundwater guesses.

 

[MTNClimber]

emmgjld - All valid points. I never had a job where 120 to 300 pcf was required. Can you elaborate on your experience with expansive soils 15 to 20 feet away from the basement wall causing movement and distress? How did you determine it was from that far away? What did the site development consist of?