Retaining Wall Design Sanity Check

[grogannc]

Would someone mind taking a look at the detail below and doing a sanity check?

 

[Bammer25]

Pretty sure that will never go anywhere regardless of your friction angle

 

[swooneyWOODSTRUCT]

At 12 ft max, footing may be close to limit for sliding

 

[Adamian]

This looks like an older detail. It is hard to evaluate the retaining wall design without information about soils. "French drain" deserves a separation from the rest of the backfill with a 12" diameter gravel fill wrapped around with textile fabric. The driveway shall not be placed over the natural soil. I'd prescribe compaction and gravel-sand underlayment. Reinforcing should be #4 @16"o.c. each way minimum. Dowel should be installed to connect SOG to ret. wall.

 

[grogannc]

Thanks for the replies. This is for a wall that was built a few months ago and compacted around 3 weeks ago. In the three weeks, the top of the wall has displaced 0.5 in per the Owner. I am trying to get information from the geotech as to what they used for backfill. The Owner mentioned he thought they had to over-excavate to get to good soil for the footing and that they just ran the equipment they were using to backfill over the area and nothing specific was used for compaction.

On the design side, it is an active pressure design assuming backfill with an internal angle of 28 deg min. I haven't seen the wall yet, am going Tues. and his 0.5 inch could be 3/8 or 3/4" so I need to verify. Also trying to get pictures of the rebar to make sure the vertical bars are on the right face.

 

[jhnblgr]

What was your max soil pressure? Did you keep it in the kern?

 

[grogannc]

What was your max soil pressure? Did you keep it in the kern?

A little bit over 1900 psf. Yes in the kern and used retainpro software (now enercalc) for the design. I felt like I was already pretty conservative with the internal friction angle as this area primarily has clay soils and there was DCP testing down to 3ft below grade where they had 15+ blow count and 10-15 at 2ft below grade. The wall steps down to 10ft height after 16ft of length.

 

[AKSherpa]

If this is a cantilevered wall(unrestrained at top) shouldn't the wall rebar be on the fill side(tension)?

 

[emmgjld]

1/2 inch movement in an 8 to 10 ft high wall is not out of the normal. The idea there will not be movement during and after backfill compaction behind this type of wall is not reasonable.

 

[geotechguy1]

You'd expect it to deflect 0.5-1% of the height by rule of thumb, so that sounds like a normal deflection. Unfortunately with a vertical concrete wall the deflection is more obvious than with segmental blocks with a stepped face

 

[grogannc]

I went to the site the other day and its barely 0.5 inches, in some places its more like 0.375. To my surprise when I got there the wall was 11'-11" from grade but only about 9'9" of soil is going to be retained. So if you run the numbers based on that, there is significant margin in the design. It actually works for at rest pressures. My guess is the contractor driving equipment over the area during backfill created some really high residual stresses.

 

[eyeforgeotech]

Interesting - nothing like a good site visit to go check it out for yourself. Sometimes reports from others in the field can be a bit misleading!

 

[dik]

I'd probably shift the footing 1' to the right and only have a 1' toe, and maybe have a few through the wall drains and tilt the wall 6" into the soil (parallel forms, but tilted). I would not have the driveway bearing on it, but have it butt to it.