Foundation for dry-stack stone retaining walls in frost belt

[stonebuilder]

Looking for feedback re: bedding material type, depth and details for footing design to support dry-stack stone retaining walls (<=5' tall)in areas of seasonal frost (N. Wisconsin). For hand-placed stone walls I'm considering a washed 3/4&quot; gravel base furnished to an economical depth (6&quot;, 12&quot; or ?&quot that would seem to minimize frost heave impacts and lead to longer wall life. Also, what is typically spec'd for mechanically-placed stone? I've seen them placed directly on soil or on 3/4&quot; untreated base. Recently moved to area from warmer climate.

 

[Grouser]

Welcome to Eng-tips.
What type of soil will the gravel pad be installed into, is the soil free draining? How long is the wall? Is the wall basically straight? Does the ground slope away from the bottom of the wall or will water collect there? What is on the ground surface in the retained soil, a roadway or structure? Are wall stones pre-shaped or naturally rounded? How thick is wall at base?

Sorry for the third degree but we need a bit more info to be able to visualize the problem. Is your primary concern appearance or durability or both or other? This will help the forum members to address your situation.

 

[kmerl]

Frost heave is an issue, but frost can act both vertical (uplift) and horizontal (pushing). So the short an long of it is the need to freely drain this wall as much as possible to keep stability.

As far as bedding is concerned I think you should use a minimum of 12&quot; of a clean stone, 3/4&quot; in size. Also the toe of the rock wall should be installed atleast three (3) feet below the ground surface. Thereby requiring excavation to four (4) feet below the surface.

It sounds like you are constructing this wall without the benefit of a soils investigation. I would like to know how much 'less than five feet tall' the wall is and what is it retaining. This may change some of these suggestions, also if it will be structural (i.e. close to driveways, buildings, etc.) you will definately need to have a geotechnical engineer design it for dead and live loads. In addition, where is groundwater and what types of soils will you be retaining?

Keithe J. Merl

 

[jheidt2543]

There are a variety of recommended details for the &quot;footing&quot; depending (as noted above) on the soil type, wall height and topography of the area. I would contact some local block producers and get their feedback. They are familiar with standard practices in the area. There is a manufacturer in Portage or Waupun, WI (sorry I don't have the name here). You can also check with some of the landscapers in the area that install the walls. The more info. the better.