Retaining Wall Design w/ Houses in Close Proximity 1

[JstBegun]

I am currently involved in designing a retaining wall where homes are to be constructed 10ft from the crest of the wall with in ground basements. The wall height is 34ft at maximum and will be segmental block with grid (Anchor-Diamond Pro 8" Block). There are no extreme crest or toe slopes involved (generally flat).

I am mainly looking for advice/references as far as methods and means of construction for the wall and internal stability of the upper ~~10ft of the wall. Obviously the upper grids of a 34ft wall would be well over 10ft (distance to basement wall from retaining wall face); therefore are there any standard practices or commercial products for providing anchorage of the grid within the 'available' reinforced zone soil.

I have done smaller walls with this same concept where CTA and/or 21A/B aggregate was used in reinforced zone. I would just like to hear some ideas or experiences anyone may have had with this type of scenario.

I have attached a simple schematic to explain.

Thanks in advance!

 

[GeoPaveTraffic]

Good Luck, this is a complicated project for someone that (based on your handle) is just beginning.

The shortened grids in the upper 10 feet of the wall should not pose much of problem, because the failure wedge is terminated by the basement wall. This will dramatically change the forces acting on the wall.

However, this also points out the problem with this design. The house is only 10 feet from a very large and flexible wall. As the wall deforms, and they all deform, the house will deform as well.

Without careful consideration of the interaction between the retaining wall on the house, a lawsuite is in the cards.

Mike Lambert

 

[hokie66]

Excellent advice from GeoPaveTraffic. The houses can't be built that close without deep foundations. In addition to lateral movement of the wall, there will be time dependent settlement of the reinforced earth itself.

 

[dcarr82775]

I agree with Geopave, the length of grid in that upper portion will not matter.

I see a couple of issues (same as everyone else):
- Even under the best conditions 34' of fill will settle a couple inches.
- MSE walls are flexible by their nature. Their performance requires them to deform and deformation means additional settlement.
- The building is well within the active zone, so you really need to design for at-rest pressures. But I am not sure if that is really possible with an MSE wall that will deform anyway.

Deep foundations are the way to go, but the grid will be more than 10' long so there is a conflict between the grid and any deep foundation. You could design the grid with 'holes' in it that would allow for deep foundation to be installed later. You could look at a mat foundation so the building moves as a rigid body, but while this will reduce cracking from distortion it will not remove the slope that comes from differential settlement.

It is a bad situation. I suggest you advise your client of all the risks and go with a deep foundation.

 

[moe333]

A deep foundation may also deform along with the wall and backfill

 

[RFreund]

I would talk to Anchor and see if they have any case studies on this situation. Spacing the grid layers closer together may help you get more even settlement almost like a GRS-IBS type system. Where the grid is acting like a reinforced soil foundation (Thinking out loud here). I know that segmental walls have been used to support permanent structures before but I'm not sure that they were this close to the wall. As for the upper grids you could bolt a steel pipe to the basement wall and wrap the grid around the pipe then extended back toward the wall (approx 3'). Check on Keystone's website (I believe) under specialty details, I think they show something on this. However as others as mentioned the active pressure would be less so this may not be necessary.


EIT

http://www.HowToEngineer.com

 

[BigH]

Thinking outside the box - given that it early on a Saturday morning - I am presuming you only have one house like this. Why not give some though to using geofoam (styrofoam) wholly under the first house - you can dig back into the SM soil to get the width - you would need to go at least 0.7H anyway for your grids. Geofoam has been used under railway abutments, highways and the like so founding a house totally on it shouldn't be a problem. You can use your grid systems on either side of the foam area. Just a thought - it might be cheaper and cleaner especially since you will need to place fairly substantial thickness of fill below the first house basement in any event (and it too would settle a bit - depending on the type of fill you would be using. Just a "throw it out there" thought.