Reduced bin pressure using geosynthetic reinforcement 1

[patucci]

We are looking to reduce lateral earth pressures (i.e., silo or bin pressures) resulting from backfill between a permanent soil nail wall and a multi-level building. Backfill dimensions are approximately 4 feet horizontal between the soil nail wall and structure and up to a max. height of approximately 22 feet. We have considered geofoam and other lightweight backfill, but want to consider a less expensive option. Does anybody have experience or references for reinforcing the backfill with geogrid or geotextile? And how to calculate what a reduction the reinforcement would have on the bin pressure? Backfill could be angular gravel.

 

[patucci]

I should add that I think a key point required for this to work is to create a space between the reinforced fill and the building wall so that tension in the reinforcement will mobilize with deformation prior to contact with the building. This space may be created using a slip form or other means during construction. I fear that such construction will not be easy or practical. Anybody with experience?? -cheers

 

[jdmm]

patucci is right. In order for geogrid to work you need to mobilize the active condition. One appoach would be to essentially build a wall using wrapped geogrid behind the bin wall and once it was completed, backfill the space. A second appoach could be to use in-extensible reinforcement such as wire mesh or galvanized straps (as in Reinforced Earth). Much less deformation is required to mobilize the full stress on the grid so that it might be possible to construct it at the same time as you backfill. The pressure would be reduced but not eliminated. The amount of pressure would depend upon the end condition of the grid (restrained or unrestrained). For the unrestrained condition it would be possible to calculate the earth pressure from a wedge or slip circle analysis close to the wall.

 

[BigH]

I would suggest that you get ahold of a paper written by Kniss et. al. entitled "Earth Pressures and Design Considerations of Narrow MSE Walls" which was written for the ASCE Texas Section, Spring Term, April, 2007. I recently got it by google using, I think, < "at-rest" earth pressure > - apparently given the date of the paper, it may be a draft or . . . Sorry I didn't save the URL.

 

[MSEMan]

The least expensive option is to construct a mesh faced MSE pressure relief wall in front of the soil nail structure. I would not use geogrids due to the strain issue - I would use ribbed steel strips or similar. Ribbed steel strips are now comercially available to anyone who wants to use them in their own designs.

The designer will have to come up with a method of tying the soil nail wall and the MSE together - this is dependent on the termination detail of the nail and the denisty of nails in the structure.

 

[Panars]

The paper referred to by BigH is located here.

http://www.ce.utexas.edu/prof/zornberg/researchgroup/people/khyang_files/Kniss and Yang (2007).pdf

There are two other papers on one of the author's website.

http://www.ce.utexas.edu/prof/zornberg/researchgroup/people/khyang.htm

 

[BigH]

Thanks Peter!