compacting wet clay during the rainy season. 1

[SiteServicesllc]

What is the best way to compact wet clay to 95% mod that is being dumped on a site that has the water table just a few feet below the surface. Not to mention that this is the wettest time of year in louisiana. I'm building a house pad and the homeowner needs to pour the slab in the beginning of january. The lot is flat with pipelines running along the only two sides with a ditch and the the pipeline company won't let me cut ditches across there pipeline to help with drainage. I'm trying to not use lime because I don't have a stabilizer. I'm looking for tricks of the trade that I may not know about. I have a dozer ,excavator,tractor with discs and dump trucks. I'm trying to purchase a padfoot compactor.

 

[hokie66]

The best way? Avoid what you are doing. You can't compact wet clay in the rainy season.

 

[Ron]

Agree with hokie66...also, wet clay doesn't mix well with other materials...it tends to clump while you're trying to mix. If you can "dilute" it with sand, that would help, but again, mixing is an issue. Can't be done properly with the equipment you listed.

Dry it by using a disk harrow or cultivator and then compact it when it is about 1% over optimum moisture, using sheepsfoot compactor.

 

[hollowstemhead]

Are the native site soils also clay? Suspect this could turn into a bathtub relatively quickly without some drainage help. Might try getting up out of the water with a layer of crushed stone wrapped in geotextile filter, then build up from there. Typically a situation more suited for a clean granular material...

 

[Zambo]

I think you'll be up to your axles pretty soon. Can't imagine how you're going to cast a slab on this.

 

[cntw1953]

Pump to drain, then do improvement as suggest. However, clay will take a long time to dry to a workable condition, maybe it is better to remove it.

 

[moe333]

You could look at lime treatment, but it's expensive.

 

[SiteServicesllc]

The only place that has sandy material is from the banks of the mississippi river. But the river water level is higher than the borrow pits. So I may have to wait for the water level to come down, which it already started coming down this week. I will definitely use sand if it is available.
I think I'm going to cut some 2' deep trenches every 20' in and around the pad site so that when I start tracking on the material the ground water will be able to flow into the trenches and not pump up into the fill that i'm going compacting. Then I'm going to stock pile the fill material in-between the trenches and disc it to dry it. as the fill material dries out I will cut the top dry layer off and use it in 6" lifts to get my compaction. Hopefully as I'm compacting it the ground water will go into the trenches and not up into my fill. Then I will have to muck out the trenches and backfill and compact them last. If anybody has a better idea that 's affordable, I'm open. As with all clients they can't see why there pad is going to cost more and take longer than there friends pad that was built in july. They also have a inlaw that is a very good carpenter that is telling them how easy it is to build a pad and he doesn't see what the problem is.
I'm sure everybody on this forum has dealt with the brother inlaw, uncle, coworker ect, ect,ect that knows more than the people that have been doing this for years.
The Smart thing to do would be wait until the conditions are better. But I'm going to try to get this pad to pass compaction for a reasonable price. They just don't know how hard it's going to be.
Thanks for all the replies it always helps to here other peoples opinions.

 

[cntw1953]

Ask the carpenter in-law has him ever build a house with fully soaked wood.

It is difficult to suggest something meaningful without knowing site conditions such as soil property and water table. Looks like you have a work plan, good luck, make sure you have enough pumps/sumps to perform continuous pumping.

 

[aeoliantexan]

You may be able to mix in lime with your disc. If Class C fly ash is available and is allowed by the environmental regulators, you can mix the dry fly ash into the soil with the disc and "dry it up". Like lime, it raises the optimum water content and is cementitious. Unlike lime, it does not need to cure for a day or two before compacting. You will need to compact it immediately (within an hour) because it is self-cementing and will begin to set up right away. Run proctors on samples of treated soil to get a fair calculation of percent compaction.

 

[oldestguy]

The above reply refers to fly ash that comes from a plant using western coal, not eastern coal. Ask about the calcium - oxide content and hopefully it will be above 25 percent. That will work great. Eastern coal fly ash won't work.

Old cement also works great.

Next, why 95 percent and percent of what? That 95 is practically impossible to get in clay and is not needed.

I'd see if I could convince inspector that if the unconfined compressive strength (by pocket penetrometer) is over 1.5 T/sf, you ought to then have a reasonably suitable pad made of clay. Tell 'em that is the bearing capacity (a pretty close to true statement).

 

[Zambo]

This thread is quite educational. I'm a civil engineer and tend to work on infrastructure projects. On first read the works suggested seem completely unlikely, but after a few responses it seems that for a "house pad" the idea is feasible.

Is there some granular fill between the clay and the ground floor slab? If so approximately how thick?

I think that the best that can be achieved is to get a clay pad that looks sound (old rejected cement if available as suggested by oldestguy would help), place a geotextile, then put a layer of granular material, proof roll and remove and replace soft spots, then test the granular fill layer. As oldestguy mentions 95% mod proctor not required. Perhaps a plate bearing test.

 

[hokie66]

Other than adequate strength, you also need to determine if the clay is subject to shrinking and swelling with change in moisture content. If it is, then this could cause lots of problems with the structure.

 

[SiteServicesllc]

How do ya'll feel about a 3ft thick sand only pad? The sand we have is a silty sand mixture that is pumped/dredged from the mississippi river into borrow pits. The sand drains well and compacts easy but when you dig the footings they have to go 1ft into natural soil. The sides of the footings can collapse if the sand dries out to much. With the vapor barrier in place I won't be a ble to use a sprinkler to wet it again. I'm worried that the concrete finishers will walk to close to the edge of the footing and cause it to cave in.

 

[oldestguy]

For me, I'd like to know more of our local regulations, such as why "1 foot in natural soil" when compacted sand should be good bearing itself.

As compared to wet clay, the sand ought to be a much better material, even if some different effort is needed.

The main risk is what you are aware of with bone dry sand running sideways. It also may migrate some laterally while compacting. However, since it is nearly a single sized material, it won't densify much with compaction, yet is relatively incompressible then. This means not much compactive effort is needed and less in the way of sand moving problems.

We used some Mississippi dredged sand material here (Wisconsin) and, when confined with enough width of fill, works well. You would not want to place the slab with its edge at or near the top edge of the fill.

Can't you form up the concrete slab edges to keep things in position at least while the concrete is setting up?

 

[cntw1953]

You didn't mention the clay, are you going to remove it, or leave it in place?

 

[SirAl]

Forget the clay. It will require extensive drying and discing under dry weather conditions let alone the rainy season. Even then, with water table at a few ft down, it will be tough to get modified compaction. Sand is not my preference in this situation. Other than stabilization/modification treatment of the clay, I would consider a coarse crush granular material placed over a fabric. This assumes that your pad will be at least 2 ft thick. Depending on the existing consistency of the clay, you might have to pad the gravel into place prior to compaction. Be careful with vibration. I'm not all that keen on the modified compaction criterion for this situation.

 

[cvg]

this may be a perfect site for a pier and beam or post tensioned slab instead of your proposed slab on grade...