Retaining wall footing

[StephNow]

I have a 2 proposed 10' high retaining walls with surcharges from nearby houses.

2009 IRC - R03.1.4.1 Frost Protection. Except where otherwise protected from frost, foundation walls, piers and other permanent supports of buildings and structures shall be protected from frost by one or more of the following methods...

Exceptions: 1. Freestanding accessory structures with an area of 600 sf or less of light frame construction and eave height of 10'. 2. Freestanding accessory structures with an area of 400 square feet or less of other than light frame with an eave height of 10' or less. 3. Decks not supported by a dwelling.

Do the retaining walls need to have the footings protected from frost?

 

[steveray]

Yes....It is not an accessory structure. At that height, it is certainly going to be engineered. What does the engineering say?

 

[StephNow]

Retaining wall footing

Well, the retaining wall is not the supports of buildings and structures. Also, there are prescriptive requirements in the IRC 10' high cmu walls.

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[fatboy]

Agreed, it is not an accessory structure in the sense that has occupiable area, but it is a structure. What does the engineer say?

 

[steveray]

R404.4 Retaining walls. Retaining walls that are not laterally supported at the top and that retain in excess of 24 inches (610 mm) of unbalanced fill shall be designed to ensure stability against overturning, sliding, excessive foundation pressure and water uplift. Retaining walls shall be designed for a safety factor of 1.5 against lateral sliding and overturning.

If it is supporting the surcharge from a nearby house, it is a building support....If it lets go and the surcharge moves, what happens?

 

[Frank]

Agree with below engineering required. Wall and footing will need frost protection designed in or it will fail and with houses on surcharge is huge potential liablity.

 

[Francis Vineyard]

In accordance with the definitions it explains that since retaining walls do not have floor area's it cannot be considered an accessory structure;

ACCESSORY STRUCTURE. A structure not greater than 3,000 square feet (279 m2) in floor area, and not over two stories in height, the use of which is customarily accessory to and incidental to that of the dwelling(s) and which is located on the same lot.

WALL, RETAINING. A wall not laterally supported at the top, that resists lateral soil load and other imposed loads.

In my opinion the language, as written, does not specifically require professional engineering for retaining walls that retain in excess of 24 inches of unbalanced fill; for example where manufacturer's provide (designed) guidelines within the set of limitations based on soil conditions. However;

R106.1 Submittal documents.

Submittal documents consisting of construction documents, and other data shall be submitted in two or more sets with each application for a permit. The construction documents shall be prepared by a registered design professional where required by the statutes of the jurisdiction in which the project is to be constructed. Where special conditions exist, the building official is authorized to require additional construction documents to be prepared by a registered design professional.

R404.4 Retaining walls.

Retaining walls that are not laterally supported at the top and that retain in excess of 24 inches (610 mm) of unbalanced fill shall be designed to ensure stability against overturning, sliding, excessive foundation pressure and water uplift. Retaining walls shall be designed for a safety factor of 1.5 against lateral sliding and overturning.

 

[steveray]

FV...Most of the "factory engineered" wall systems I have seen require a soils analysis or some other specified piece of engineering that usually gets them...

 

[steveray]

Like these.....

REINFORCEMENT (IF REQUIRED)

• Geosynthetic reinforcement is recommended

for walls taller than 4 feet 6 inches, or walls

situated in poor soils, supporting a driveway,

etc. Consult an engineer for design assistance.

• Check the wall construction plan to

determine which courses will need

reinforcement.

A geotechnical engineer should evaluate the foundation soil to

verify that there is adequate bearing capacity for support of the

structure before placing aggregate in the trench.

 

[Francis Vineyard]

steveray, our mileage vary with recommended and consulted on a case by case basis. Is that Dia. Pro?

 

[Francis Vineyard]

delete double post

 

[steveray]

steveray, our mileage vary with recommended and consulted on a case by case basis. Is that Dia. Pro?

I don't remember...I don't do alot of them. I had one this spring that was a replacement at some condos that was failing from 20 yrs ago or so (same contractor repaired via lawsuit) It is holding the buildings uphill....no slack. Those instructions called for specific eng analysis of the soils I think it was...

 

[Francis Vineyard]

Good call; soil erosion and drainage collapse over time cause lots of failures here.

I would add that IBC 1610 and 1803 has similar language; there are other sections that do indeed require a RDP stamp in seismic areas (load combinations).

Didn't require an engineer for the wall in the photo below; after I took this picture was walking back to my car when the earthquake in Louisa occurred. Thought I was starting to suffer from vertigo until I heard the news; thanked goodness!

 

[jar546]

It is not prescriptive per the IRC, therefore it must be engineered. The RDP will call out frost protection.