Caisson Quay wall cohesive fill stresses

[GeoGeoGeo]

Hi everyone,
Our client wants us tu evaluate the earth pressures due to the caisson fill. We have always use granular backfill with the usual narrow backfill theory (silo effect). However with a cohesive fill from a dredge can we still use the narrow backfill theory?

Many thanks

 

[SlideRuleEra]

We have always use granular backfill with the usual narrow backfill theory (silo effect).
However with a cohesive fill from a dredge can we still use the narrow backfill theory?

I definitely would not.
Silo effect happens when using granular material (sand/gravel, grain, crushed coal, etc.).

Cohesive material (like clay) is not granular.

There is no control of the quality of dredged material... just what ever is dredged up (pun intended).

Angle of repose for dredged material is low, making it act more like a fluid.

 

[GeoGeoGeo]

Yes I agree with you, the material that is going to be dredged is clayey silt/Sandy silt and It makes sense that when the cell is filled it is is going yo behave as a liquid so i believe that two hypotheses could be checked:
1)Calculation of horizontal stresses on the cell wall considering that we have a fluid with a density of around 12 kn/m3. Earth pressures coefficient to be used k=1

2) Consider the water stress (d=10kn/m3) and k=1 plus de horizontal stress of the hydraulic fill (density = 14 kn/m3 with a k = 1 - sen 20 (being 20 the supposed friction angle of the material). As we would estimate effective stresses the submerged density would be 4 km/m3 so the results should be quite similar to the first approach

Thank you very much

Kind regards