Rigid Insulation Beneath Retaining Wall 7

[KootK]

My client is adamant about having rigid insulation beneath the footing of an exterior retaining wall that I'm designing. The footing of the retaining wall will be built at an elevation above frost depth. I have two questions about this system:

1) My client believes that the rigid insulation will provide protection against frost heave, both wholesale and differential. Can anyone explain to me why rigid insulation so placed would be useful as protection against frost heave? I'm sceptical.

2) I'm worried about the insulations ability to transfer shear from the footing into the soil. Anybody know where I could find friction coefficients for concrete in contact with insulation or insulation in contact with soil?

Thanks,

KootK

 

[concretemasonry]

KootK -

What is the lentgh of the wall and what is the height retained and length?

As BA said, it may be more practical to allow it to float OR move depending on the temperature if it is a relatively low wall and not attached to a structure. That may eliminate the practical rigid wall design for this application and may be more in the realm of the "geo" types to design.

A flexible wall may serve the purpose since they have a history of performance.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[KootK]

Thanks for all the info dik.

@ concrete masonry: the length is about 20 m and the retained height is about 1200 mm. I've been considering it a floating wall all along.

 

[a2mfk]

Maybe a key on the bottom of the footing will help with the sliding and the rigid insulation so you are not relying on friction.

 

[KootK]

Thanks for the suggestion a2. I'm not sure that I have it in me to through a key on a retaining wall this small however...

 

[concretemasonry]

For such a small wall and height, I would look at a segmental retaining wall(SRW) that never has a rigid footing and can absorb distortion from frost heaves. It is not an item for a structural engineer to design since the system is used internationally for wall up to 40' high. - Usually a geo engineer if over about 4' to 5'.

No foam insulation is required even at the north pole.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[dik]

They can look better and I haven't priced one out lately, but a couple of years back they were similar in cost per sq. ft.

Dik