Retaining wall crack, solution to fix please! 1

[dannyypk]

I am in the process of investigating a retaining wall. It is a shape of \___ The short side (the diagonal) is about 10' long and the long side is around 26' long. It is a 6' tall wall (meansure from the top of footing). The wall is a drive way retaining wall, so the back side is only 5.5 ft back fill with concrete slab on the top. It was built up using only 8" CMU blocks with #4 @ 24 "o.c. Footing was around 3'-0". The building built it without any design.

There were two vertical crack in this wall. First one occur @ the joint where the diagonal meet the horizontal. The other crack occur @ 2 ft from the right end of the horizontal wall. These two crack are both veritcal crack and from top to bottom.

The Builder was seeking soultion to fix the wall in order to get the CO. I had suggested him to use the wall anchor to tie the wall back, but the company charge him 6500 for 5 anchor. So, he was seeking another economical solution.

I am thinking building up some buttress behind the wall.
How do I design an adequate buttree to support the wall?
and any other solutions?

Thank you!

 

[hokie66]

Sorry, but for an incompetently built wall, there is not much you can do other than start over. The builder should seek professional advice before construction, not after.

 

[msucog]

also, the backfill should be well compacted. so whatever the fix or rebuild is, make sure the backfill is done correctly. if placed incorrectly, any errors or subpar designs may find themselves in the "failing" category. some incorrect designs may hold up fine over the years if the backfill is properly compacted and drainage provided.

in my opinion, backfill placement and drainage are about 50%+ of a free standing cast in place concrete retaining wall functioning "properly". foundation is probably 40%, backfill say 50% and wall itself about 10%...let's not forget the contractor that can easily add another 50% to my figures above since they are quite often capable of screwing up almost anything.

 

[hokie66]

msucog,

I don't argue with proper placement of backfill, but in my experience retaining walls fail due to inadequate design and/or construction of the footing and wall. Building an inadequate wall and then trying to rectify it by tweaking the backfill is not the answer.

 

[msucog]

no i agree (i guess 10% is a little exaggerated to the low side). my point is that if the wall is designed with the assumption of certain soil conditions and then those soil conditions don't exist, it's possible that the design doesn't matter a whole lot in the long run. and everyone knows of walls that stood up fine when either the wall design sucked or the backfill/foundation sucked. i'm sure we also know of many more times when such things caused failures, undesirable settlement, rotation, cracks, etc. both parts are essentially to a fully functioning wall. the design should be appropriate for the site conditions and the construction should be appropriate to satisfy the design requirements.

and building anything inadequate and trying to psuedo-fix it after the fact is just silly in my opinion. it costs many times more to "fix it" (usuallly doesn't solve the problem, just extends the amount of time until someone has to "fix it" again) than to just do it correct the first time.

 

[dannyypk]

How ever, I am still trying to seek any possible solution, I understand there is not too much choices....

 

[msucog]

it seems to me (based purely on my understanding of the wall height, materials used, etc) that it would be more cost effective to have the contractor take it down and replace it with an adequate wall (properly designed and constructed). it sounds like it may be more expensive to try and fix things in place for a semi-fix. perhaps others can offer better advice.

if it's a permitting issue, sometimes making the wall under a certain height lessens the requirements for a CO. if it requires a stamp, i wouldn't stamp it unless i designed it and oversaw construction and testing.

 

[apsix]

Remove backfill and replace with no fines concrete or cement-stabilised sand (with adequate drainage), thereby converting it to a gravity wall. It won't be cheap.

 

[kslee1000]

If there is adequate space in front of the wall, with no land-right issues, then you may want to investigate the possibility of extending the base slab, and add the buttress in the front side of the wall.

 

[oldestguy]

Vertical cracks? Why the concern? Does it look like the wall is tipping or bulging? Sounds more like the foundation is settling differentially, yet the backfill is being retained.

I'd sit back and re-evaluate what this wall has to do and if it is just appearances, maybe some agreement for accepting a wall that does not look perfect.

 

[DRC1]

How wide are the cracks and do they penetrate the fullThickness? Is there evidence of lateral displacement. I agree with oldestguy that it very well may not be due to lateral movement. Another cause may be shrinkage, esp. if the conc. was poured wet. The wall bend would be a likely place for the crack although the 2 ft from the end seems odd, which gives oldestguys settelement theory creedance. A sixfoot wall is hard (but not impossible) to screw up for overturning.

 

[dannyypk]

It was a masonry retaining wall. I think what I gonna do is to cut out the slab, remove the back filled about 4 foot wide. Pour a 4ft wide x 3 ft tall concrete behind the wall. it will work like a counter fort and stop the wall from pulling out.

 

[hokie66]

Your solution sounds much like the one proposed by apsix, which is a reasonable approach. The wall will be converted into a gravity retaining wall rather than cantilevered.

Be careful in placing the concrete or stabilised sand. I wouldn't go more than about a foot in a lift. If concrete, wait until it achieves initial set (you should be able to walk on it). If stabilised sand, I would require a day in between lifts.

The vertical cracks in the blockwork will still be there, but you may be able to conceal them satisfactorily.

 

[MSEMan]

Why don't you excavate out the existing fill and build a MSE wall 12" behind the existing wall?

Use wire mesh facings and wrapped geogrids or geoynthetic sheets. While some codes require 8' minimum geogrid lengths, you can get it to work with 6' lengths. It's pretty easy to design and will cost about $8 / s.f.

When construction of the wire faced wall is complete fill the void with single size rounded 5-10mm gravel.

 

[dirtsqueezer]

Just a thought. I agree with Oldestguy, sounds like it wouldn't be a monumental concern. Maybe take a sample of the backfill to your friendly neighborhood soils lab and have it analysed for liquifaction, expansion, ect. just to make sure it's not the fill. Here's a thought though; was the CMU filled with concrete? There are a lot of CMU walls associated with building that don't get filled. If that's the case, it's very easy to get cracks in the wall. And the solution is easy- fill it. Just a thought.

 

[civilperson]

Cover the cracks/wall with parging and live with it.

 

[Bluefoot]

Studies suggested the main causes of retaining wall failures. Figure: Summary of Experience with Unsatisfactory Retaining Walls
from USACE EM 1110-2-2502 pg 6-16