Any way to reinforce an under-designed retaining wall?

[inaz]

The structural engineer on our project just told me he way under-designed his retaining wall. He apparently plugged wrong data into his computer program. It's an 8-12 feet high wall with a backfill slope above the wall of at least 1.5H:1V, so loads are pretty high. I'm thinking maybe a few feet of concrete backfill placed in lifts and allowed to cure between lifts. Also maybe perpendicular deadmem walls, but then we're in a restrained case. Any thoughts would be appreciated. Thanks.

 

[PEinc]

Can you be more specific? What is under-designed? Footing size, bearing, eccentricity, reinforcing steel (footing or stem), etc.? Do you have too low of a safety factor (sliding or overturning)?

 

[inaz]

Good questions. From what I've heard it sounds like the footing and stem widths, and steel are too thin, but I'll get more info this afternoon in our site meeting.

 

[msquared48]

At 1.5 to 1 backfill slope, any chance of putting in a secondary retaining wall above the first one to lower the soil pressure to the first wall? Do you have enough room to the property line?

Any chance of tiebacks or soil nailing (easements required?)to reinforce the wall. Any recommendations from your geotech?

Counterfort walls might help the stem wall depending on the stem wall steel placement and size, but probably not the soil pressures.

Mike McCann
McCann Engineering

 

[PEinc]

Is the wall already built? Backfilled?

 

[oldestguy]

I've seen a cantilevered wall with steel in the front face by mistake. You can't be much worse that that for under designed. However, it leaned some, but stayed put. Later on, someone drilled through it and used tie-backs to keep it there.

You can always put struts in front until some improvement can be made.

My old reinforced concrete design prof made the comment once. At least get steel in there and you will be surprised what seems to work.

 

[valleyboy]

It may be possible to excavate at the rear of the wall and instal some lightweight EPS fill to reduce the lateral loads to within the capacity of the as-built structure - similar to sheet 03 here:-

http://www.cordek.com/docs/std_details_LightweightFill.pdf

VB

 

[aeoliantexan]

I once used a geogrid-reinforced backfill behind a lightly-reinforced masonry wall in a parking garage. The soil was contained by geotextile and geogrids wrapped around each lift, and a gap was left between the backfill and the wall. The floor slab was designed to span this gap, and the geotextile was trusted to last in this dark space. Be sure to drain the gap!

 

[MSEMan]

If you can excavate the top few feet of the wall you can install a zero load MSE pressure relief wall down to the stage where the reaction can be accomodated by the wall.