Stabilizing loose sand and void under slab-on-grade

[ajk1]

Is there a reliable injection technique to increase the strength of a localized area of loose wet sand under anexisting 50 year old slab-on-grade? Please see the attached drawing. The area is about 9 feet by 25 feet and investigation indicates it is a very loose wet sand type soil and there is void space immediately below the slab, varying from about 1/2" to 4"±. The general surrounding area is a stiff clay, as determined from bore holes.

Is there a material that can be injected into the sand to stiffen it up, and if so, what is the material? It likely will end up finding its way into the weeping tile, so the weeping tile in the area will likely need to be replaced.

The alternative is to temporarily laterally brace the basement wall, remove the slab-on-grade in the affected area, remove the loose wet sand material and place a controlled density cementitious fill and a new slab-on-grade. This seems expensive and I want to know if there is a more cost effective solution.

 

[Ron]

ajk1....you might consider foam injection such as a method. I've used it for soil stabilization in loose sands and works well. One project was done about 10 years ago and has been performing well.

Here's a link to one such product...there are several......Stabilization

 

[ajk1]

Thnaks Ron...I will check out the link

 

[oldestguy]

I'd try to stabilize the sand in case it migrates due to vibrations. Stabilizing contractors have many ways to gel up material that has voids suitable for thin liquids.

I am not in the stabilizing business, but I understand one of the earliest materials is called water-glass, apparently used for preserving eggs. My old boss, B.K. Hough worked on a process called chrome-lignin, a waste liquid product from paper mils that had some stabilizing properties. Even "mud-jacking" contractors might fill the bill here.

Hey Ron, there is a famous football game on TV.

 

[ajk1]

Ron - do you know if there are any contractors in the Toronto area specializing in the process? Come 9 a.m. I will call the number on the link that you sent me and see if they market in the Toronto area.

What did you do about the issue of potential clogging up the weeping tile with the injection material?

Have you any feel for what this costs? Our geotechnical engineer says that it is very expensive process and it is cheaper the excavate and replace the material below the slab-on-grade, but I find that hard to believe.

 

[darthsoilsguy2]

uretek does urethane injection too and i see they will service NY state.

http://www.uretekholdings.com/

 

[jayrod12]

Uretek existed in the Canadian prairies a while ago too. I believe they may have changed names now though.

 

[ajk1]

To Darthsoilsguy and Jayrod - It is rare for a contractor to operate in both New York state and the province of Ontario, but I will check it out on the internet. Thanks.

I am still interested in hearing from anyone as to whether the injected material can find its way into the weepers and how that issue has been dealt with.

On another matter, does anyone know why this forum no longer sends notice to me gmail when someone replies to my post? When I initiate my post, I check the box that says notify me when someone replies, but still it does not do so. It used to do this.

Andy

 

[jayrod12]

They come in a different folder in gmail. Might be the promotions, or social folder. Maybe even the junk mail.

I don't believe it is that rare. Uretek was a national (possibly international) company. So it may not be the same contractor, but it could be under the same title. Essentially it is poly-urethane injection.

I haven't heard of any issues with the foam causing problems with weeping tile, although you could try talking to them and seeing what they say.

 

[oldestguy]

I assume your word "weepers" means underfloor seepage collecting drains. Could it be that the reason for the voids now present is that sand has been lost via those under-floor drains along with any water draining? It happens if the drains are not properly filtered, a common failed clear stone backfill situation. Thus, almost any of the usual mud-jacking, pressure grouting methods, etc. likely will fill those drains, as you are questioning. Short of some method that won't do that, you may consider flushing the drains and observe the outlet for signs of what ever grout or injecting material comes along as a way to control that underfloor filling work. Adding water to the area these drains are protecting may cause unexpected problems. For instance I know of one case where the site had compacted high plasticity clay supporting the building and the roof drains were connected to a sub-drain system outside the building. Water fed from those drains flowed back under the building in sand filled utility trenches. A major floor heaving developed. A well intentioned architect's plan backfired.

 

[oldestguy]

A second thought. Compaction grout interject well below the voids, lifting the ground, may work, but that method had to be carefully monitored for lift and grout going to unexpected places.