Thickness of Granular Material Behind Retaining Walls For Buildings

[VAD]

What is the desirable thickness of granular material behind basement foundation walls or concrete retaining walls in general and what rationale is used to determine this thickness? Does the thickness influence your recommendation of lateral earth pressure coefficients?

 

[fattdad]

If used for drainage, I typically recommend 12 inches. If used to control the horizontal earth pressures, it would depend on the wall height. That said, you would be able to graph the width versus earth pressure and see how it would affect your design (or the cost thereof). Full active earth pressure is realized when the envelope of 45+phi/2 (measured from the horizontal) extends from the base of the wall to the ground surface. For at rest, you could use a similar envelope, but you'd likely have to increase the earth pressures by the ratio of K0/Ka.

Just some initial thoughts.

f-d

¡papá gordo ain’t no madre flaca!

 

[oldestguy]

Hi Guys:

I have come to the conclusion when it comes to detailing something to be done just so, that it seldom happens. More often than not, well meaning and "lazy" workmen just do it the easy way. Instead of carefully placing 12 inches next to a wall, a whole bucket load from an end loader is dumped in and maybe spread a little, but more likely not. Ask for 12 inch layers and they vary from 6 to 20 inches, or more.

Thus, it is easier and about the same cost to spec. the whole backfll to be granular fill, to be sure you get what you want.

So, the simpler you can make it, the more likely it is done right where you need it.

These things are stated since these days it seldom possible to be aware of everything on a job, especially non critical work.