Bagged Fill

[masterthenight]

Does anyone have any information on the effect of bagged fill located behind concrete grade beams/walls? An Engineer at the company I work for is telling me that with bagged fill, the active pressure from the soil on the beam/wall can essentially be neglected. I have asked for technical information to that effect but he does not have any. He is operating based on his 20 years of experience and also the fact that this type of construction is common throughout our local area and that foundation with that type of construction have not failed. I expect this type of rhetoric from contractors, but this is coming from internally. It's quite odd to me, he is asking me to design and seal designs which utilize this reduction and I am resistant since I have heard nothing in my 12 year engineering career on this (admittedly I am still young).

The detail my company uses allows up to 10'-0" deep perimeter grade beams with no footing at all. They don't even design the grade beam as a retaining type structure.

I looked online for a bit but got absolutely ZERO results, which furthers my uneasiness.

Any input is greatly appreciated.

 

[TehMightyEngineer]

Well, wouldn't the bag limit the force of the soil? Consider a sand bag wall, the sand would normally assume a sloped pile but the bags limit the sands movement to a point. Beyond that the load from the soil is taken by the bags structure (you don't feel a soil pressured by resting your hand on the bag). But, if you lift up a bag (remove the tension in the bag) then you will get the full weight of the soil. So, the first step is to make sure that the bagged soil is self-supporting and not resting against a structure.

The other thing I can think of is that soil pressure could still be transferred through the bags. I would imagine the bags as something like buried rocks, they reduce the active pressure but don't eliminate it entirely. Though, as the bags aren't rigid like a boulder they would absorb a fair amount of lateral load and would definitely distribute it outward.

I'm curious to see what other people say, though.

Maine EIT, Civil/Structural. Going to take the 1st part of the 16-hour SE test in April, wish me luck!

 

[Ron]

I'll give you a great engineering opinion....it depends.

If the retaining wall is not in deforming contact with the bags (if the bags are not smooshed against the wall), then the soil will exert no pressure on the wall. If the bags are smooshed against the wall, the soil will exert pressure on the wall, similar to the way free soil would although probably a bit less because of the friction of the bags, etc.

 

[cvg]

you might find some information here

testing of earth bags

http://earthbagbuilding.com/testing.htm

http://www.texaswafflemat.com/baggedfillfoundationwwm.htm

 

[masterthenight]

Thanks for all your replies. Sadly, I feel the replies in this thread are indicative of the information available on this subject - pretty scarce. It does seem clear that the bags will help to reduce the pressure on the wall; however, by how much is the real key. I can think of scenarios where it would reduce it by a lot and others where it would transfer the full lateral pressure - with little control to ensure a given outcome is achieved in the field. Thanks again for sharing your insights and resources, they have been very helpful.