Length of Backfill to provide passive pressure to a concrete block foundation

[Geotech East Ontario]

Hello,

In the assessment of passive pressure, the parameters required are usually the height of backfill, the unit weight, and the coefficient Kp. Please see the two attached images. I have a this arched structure with concrete block foundations which are pushed outwards due to the arched shape of the structure. How can I assess how much backfill to place beside these block foundations so that they remain in place due to the passive pressure from the backfill? How do I work out the length?

Thank you for your help in advance.

 

[Smoulder]

Look up Coulomb and log spiral passive wedges. If you have a retaining wall to contain the fill then you need to add on the active zone length so it doesn't interact with the passive zone. Look up anchored sheet pile walls for this.

 

[DaveAtkins]

Agree with Smoulder. The horizontal length of the wedge will depend on phi if I remember correctly. The horizontal length of the wedge will be at least twice the height, and could be three or four times the height.

DaveAtkins

 

[EireChch]

Relying on some backfill to provide restraint against lateral movement is not a good idea given how close to the surface you are. I would put in a lie of sheet piles

 

[PEinc]

I would expect tie rods connecting the foundations on two sides of the building to be a more economical, more typical solution for resisting outward lateral thrust.

http://www.PeirceEngineering.com

 

[MTSOE]

I would recommend checking whether you can develop the necessary horizontal resistance through friction between the block and the ground. Backfilling with soil next to the blocks may not be necessary at all.

If you can't develop the required resistance, then decide which theory of passive pressure to use for the backfilled soil (rankine, log spiral, etc.). It then becomes a geometry problem with phi as your input.