Grout Void Filling Procedure

[GGeotechEng]

Does anyone know where I could find a procedure for grout void fill?

 

[SlideRuleEra]

See if what you need is in the technical papers available at this link:

http://www.haywardbaker.com/WhatWeDo/Techniques/Grouting/CementGrouting/default.aspx

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[oldestguy]

It depends on what your goal is. I see the Hayward=Baker info on slab jacking doesn't say much. Nothing said about keeping the grout from escaping, etc. The mix also is an interesting subject.

If your goal is merely filling a void, that is one thing. But lifting a slab or fixing some problem, it can be complicated. Grouting takes the easiest path and not fully knowing that path sometimes will back fire on you.

I'd talk to an experienced grouting contractor. Slab jackers are a dime a dozen, so be careful.

 

[BigHarvey]

As oldestguy says, it dépends on what your goal is. This type of grouting is generally carried out in several stages. First one is to fill the void with a mortar (grout with a load od sand or ashes or whatever is available and economical in your area) which dépends also on the type of void ( karst, mining, etc). Second stage will be pressure grouting with a bentonite cement grout to complete the treatment. Quantities and max p^ressures depend on the surrounding ground and you goal (watertightness, reinforcement). If you need to provide spec and this is not your cup of tea, I would advise you to ask to somebody with experience in grouting. A specialized contractor might be able to help you, provided he knows the whereabouts of your project.

 

[crcivil]

What kind of soil is that you are planning to grout? What is the purpose? Is there any information concerning the soil's moisture content, N-SPT values? Basically what you do for this kind of application is to design a grout mix whose compressive strength is just about higher than the native soil's being treated. Then you trace a grid pattern typically of one 3.5"-4-0" borehole every 4 to 6 feet and at a depth where you have decided the tratment is needed.

If grouting pressure control is not a paramount issue, you can skip using a tube a manchettes and just place a perforated pvc pipe to avoid soil from slaughing into the borehole. You then strenghen the top of the borehole so that it can stand the pressure while grouting. You do that by placing a small footing around the top of the pvc pipe.

You can seal off the entrance of the borehole with rubber while placing your 1"-2" grouting pipe up to the bottom before you start grouting with a trailer concrete pump or a moyno type pump (depending on your mix characteristics). Grout in alternating fashion up to refusal of the grout, i.e. boreholes number 1,3,5.. first then 2,4,6 and so on, expecting to read pressures of about 2 to 5 kg/cm2 on the manometer.

Here is a good book with a whole chapter on the topic:

"Ground Control and Improvement" by Petros P. Xanthakos

Hope this helps. Best regards.

 

[mudman54]

i'm not sure why you were provided a link to "high mobility grouting" info; if anything you need low mobility grout for filling voids as most geotechs understand. as others have commented above, more info is needed to evaluate many options and economics.

 

[Mccoy]

I'm interested into this topic since probably I'm going to be involved in some project of natural and artificial cavities-filling underneath old residential structures. such structures must be retrofitted or just rebuilt after a large earthquake. I found really little literature on cavities filling. Some recent developments are low-density products such as laterlite and resins. One concern is swelling stress, if the structure must be preserved.
Another concern is cost, when the cavities are relatively large, also, concrete may cause settlements at the bottom of the cavity (which may propagate to the foundations). It may not be possible to achieve with a reasonable accuracy the strenght of the natural ground. What happens if strenght is significantly larger or lower, Thermal effects from large concrete masses, and more...
I looked up the TOC in Xanthakos' et al. book, but didn't find a chapter specifically dedicated to filling of cavities.

 

[crcivil]

Mccoy, you might want to take a look at this publication:

"Grouting Methods and Equipment" USA Department of Defense

http://www.vulcanhammer.net/geotechnical/ufc_3_220_06.pdf

Regards.

 

[Mccoy]

Thanks crcivil, in that publication there is something on fillers for grouting cavities

 

[SlideRuleEra]

McCoy - In 1980 I was involved in a sizeable subsurface grouting program at the site for a major electric generating station (the plant site was about 1 square mile, cost of the subsurface investigation / grouting program was several million dollar, in 1980 dollars). Since that was 33 years ago, reviewed the "Grouting Methods and Equipment" document that crcivil recommended to refresh my memory; thanks crcivil.

Soil boring revealed an extensive network of solution voids in underlying limestone. Most were from a few inches to 3 feet high and were continuously filled with ground water. The plant site was in the coastal plain of the southeastern USA, water table was essentially at ground level all year.

At the location for heavily loaded foundations an extensive, planned & regular pattern of holes were drilled. The drill rig crews quickly became very competent at detecting voids and their approximate height by monitoring loss of fluid circulation and sudden drops in the drill shafts.

At holes that the drill rig crews indicated voids were located pressure washing was used. A rotating nozzle allowed water to be forced horizontally in a 360 degree arc, inside the voids. While washing was going on, nearby holes were monitored for indication that they were connected. Often the results were quite dramatic - when the pressurized water forced its way through enough of the debris in the void network, connected nearby holes (and sometimes holes not nearby) would erupt like a geyser. Remember water table is at ground level, so there was no gravity head to overcome for the wash water to emerge at the surface.

Pressure grouting was preformed at the holes that were pressure washed. Connected holes were monitored for indications that sufficient grout had been injected.

At one particular location a single large void was determined to be about 12 feet high. It was pressure wash as much as possible. Rather than try to fill this void completely, a spaced pattern of geotextile bags were inserted into the cavity through drill holes. Once in place, the bags were pressure grouted one at a time, from bottom to top. This formed a series of grout columns (inside geotextile bags) to support soils above the cavity.

Time has shown that the grouting program was a success.

We did try to use ground penetrating radar to locate voids, but that technology was in its infancy an was not successful

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[Mccoy]

We did try to use ground penetrating radar to locate voids, but that technology was in its infancy an was not successful

SRE, that's a nice story, I can visualize the extensive network of karstic cavities and the way they sprayed water geyserlike when the groundwater was pressurized.
Nowadays the favorite method to locate cavities would probably be electrical tomography and it seems to work all right with dry cavities, but in your case it probably would not have detected them since they were totally water-filled.