ROCK DOWELS FOR RETAINING WALLS 1

[soiset]

I am designing a wall retaining a 1.5:1 back slope. The wall will be more than 9' high above finish grade (acp) and will probably be 11' high total, with the base resting on basalt. To prevent sliding, I was wanting to dowel into the rock with the #6 bars that are also the tension steel for the back of the wall (14" oc). Would this create a case in which the wall would have to be designed for passive pressure as opposed to active, ie would the wall not yield slightly because of the rock dowels?

Chris

 

[CarlB]

No, would still be active case, because only wall tilt is necessary to achieve active condition, not sliding. Dowels wouldn't prevent wall tilt. Same as if you had a key in the base, or socketed the entire base in the rock.
That's my take on it,
Carl

 

[ishvaaag]

With Cohesionless backfill you need
lateral tip deflection/height>0.001 to 0.004 for dense to loose sand backfill to achieve active push status.
Check if you have as much

For more see table 2.2 p. 74 in
Bridge Substructure And Foundation Design
Petros P. Xanthakos
Wiley

 

[DRC1]

If you put the dowels on the heel side, you will prevent tipping as well as sliding. In order to obtain active pressure, the wall must yield slightly as Isvaagh points out. With grouted anchors I would not count on active pressure. However you probably won't get passive pressure either, as that would require the wall to deflect backwards. You will have an at rest or ko condition. This is the pressure the wall exerts on the wall if the wall does not move. Although you should check your soil conditions aginst a text such as Bowels "Foundation Design", the value for ko in sands usually ranges from .65 to .45 with .5 being a typical value. But again you should check your conditions against a a good text book.

 

[Sean2]

I would caution you on the corrosion path which you create by extending the steel from the back wall into the rock. Water will find its way along the wall-rock interface, and some corrosion will occur. This will affect the ability of the steel to provide the dowelling action AND the capacity of the steel to resist bending in the reinforced concrete wall.

I strongly recommend that you consult a geotechnical engineering specialist when assessing the loads exerted by the retained material and the stability of the wall.

 

[reddog99o]

Boy, great info here folks. If you want to force the wall into passive, bolt it down with Dwiydags (sp?) and stress them up as you feel necessary, just be careful you don't pull it too far back. That'll be take care of the sliding and rotation, but it's probably a bit of overkill. R.A. Hassett, P.E.
rah1616@hotmail.com