new house with driveway under mining (construction, contractor, best)

[newbuilder55]

Built a house a year and a half ago and now noticed lack of soil beneath one section near the garage. Same thing under part of walk to front door. Had a one year warranty and contractor has said he will drill holes and pump something in to fill in the void. Is this what should be done or should the section be replaced? Also seems to have some sinking around part of foundation. Should the contractor fix this also?

[oldtrader]

How things are repaired, depends on why is the soil sinking. The reason, will dictate what is the best way to solve the problem. A couple of possible reasons for problem. And there are other possibilities.

Home built on fill that was not properly compacted, or on unstable shifting ground.

There is a water flow under the surface, from a spring, natural drainage when it rains, etc. washing it away. One cause of the sink holes, I know you have read about or seen on T.V.

It is important that the reason for the sinking of the soil, as you have to consider that the problem may continue to happen and even accelerate in the future and steps need to be taken to end the problem, not to just patch what you see now.

It sounds like what the contractor is proposing, is just pump concrete under the walk, etc. to fill the void from the missing soil. A good patch under the walk as an example, if that was the only place with the problem. However as you see it starting to happen around the house, a quick patch a couple of places, does not end the potential for additional problems you are starting to observe. You need a soil specialist to check out the problem, and to give you advice on how to solve the problems so you don't have problems in the future.

[newbuilder55]

Was told the fill was not properly compacted. Wouldn't this cause the soil around the foundation to sink after all the snow and rain we have had this year? Will the sinking hurt around the foundation other than the cosmetic look or should more dirt be brought in so water will not accumulate close to the foundation? Isn't this the responsibility of the contractor?

[Arrby]

The soil should have been compacted, then five inches of gravel laid down before the concrete was poured. Depending upon your location, the soil may contain a lot of bentonite, which swells and contracts alarmingly, compounding the problem.

This is almost never done adequately. It often is not done at all. Frequently I find driveways poured over no gravel at all, more commonly just an inch or two.

What the contractor is describing is a process known as "mud jacking". Holes are drilled and a soil-cement slurry is pumped in under pressure to fill the voids. If the concrete is not broken, this can be very effective. As noted above, however, if you have a drainage problem this will not solve that problem - the water will just go around or under and create new problems.

If you have soil subsidence around the foundation it may be a major or minor problem. It is impossible to say without seeing it. With luck you might need nothing more than a few shovelfuls of dirt. Yes, you want the water to flow away from the foundation, and more, to drain away under the surface. This should be part of your guarantee.

Yes, the recent rains are going to show up drainage and soil compaction issues.

[sunsprit]

You didn't identify the location in Colorado where this is happening.

Be aware that bentonite soil issues present in much of the Colorado front range area.

Even with appropriate soil compaction at the time of the site prep and concrete pour, it wouldn't be uncommon for sub-surface (seasonal) stream flows and the effects of the expansive soil to create a wash-out situation.

You must determine if bentonite soil is present under and/or adjacent to the concrete surfaces. If so, you are looking at a rip-out of the concrete and properly preparing the substrate. An effective moisture barrier may be required to divert sub-surface water away from the developed area to minimize the problem.

I've seen some areas where a french drain system leading to a catchment and a sump pump is required. As well, you may need to check the house foundation area for movement.

Yours wouldn't be the first structure in Colorado built on bentonite soil without having received appropriate engineering and remediation before construction began.