Gravity retaining wall design 1

[bsda11]

Hello everybody,

I need some input on a design of a gravity retaining wall
up to 10' in the area of hard clay/sandy soils.

The wall is to be made of 2'x2'x6' solid concrete blocks
with a key lock on the top.

Does anyone have experience with this type of a design ?
Any comments or input are appreciated !

 

[ishvaaag]

Rarely a single layer of such thin blocks can out of gravity retain the soil behind, hence some buttresses, normally in the fill side at least, and better, cellular construction should provide for the wanted stability and strength through gravity. Also, better use excess excavation and cohesionless backfill to better warrant the then assumed behaviour, especially if you see it is likely the clayey soil will show important volume change. Reinforce the built walls, and if cohesionless backfill, drive drainage waters to known channel or sink able to take the flow.

 

[geomo]

Get this reference:
Collin, James G., Ph.D, P.E., Editor, "Design Manual for Segmental Retaining Walls," Second Edition, Second Printing, National Concrete Masonry Association (NCMA), Herndon, Virginia, 1997.

Also get the program, SRWall2.1 from NCMA. Call (703) 713-1900 and they will send you a manual. There might be a charge for the materials, but they are a non-profit association, so it will probably be small. The program, SRWall2.1 has a feature that can be used to design gravity walls with modular blocks. You would need to input soil properties such as angle of internal friction, cohesion and unit weight for the retained soil and foundation soil. You will also need to input the block geometry and weight and some data regarding the frictional interface between the blocks. With that information, you can input the height of the wall you are designing, and the program will tell you if the proposed wall is stable.

If you are familiar with basic soil mechanics and you do not want to get the NCMA materials, you can use a Rankine or Coulomb analysis and basic statics hand calculation to determine the wall stability. For a ten-foot tall wall, I would assume that it will be made of five rows of your blocks stacked on top of each other. Start with the top block, calculate the earth pressure imposed by two feet of backfill behind the block, and see if it will slide or topple over the block beneath it. Do the same for the next block using a four-foot backfill, and repeat for the remaining blocks. You will probably find that lower rows of blocks need to be aligned with the long direction pointing into the wall, or maybe with the blocks parallel to the wall but with multiple blocks placed one in front of another at each level. Then maybe you can build the upper rows with a single block placed parallel to the wall face. The final wall section will resemble a stairway, stepping down from the top of the wall into the backfill.

If that requires too many blocks, consider using geosynthetic reinforcement to stablize the backfill and allow the wall to be built with a block veneer.

Good luck.