Wall Cracking During Well Installation

[WiSEiwish]

I currently live in a house that is on a well. Last summer the well had to be replaced. During the driving of the new well casing the house moved at about 25ft down and there appeared several cracks in the drywall on the upper level, but also cracks in the masonry foundation wall. The installers stopped, then finished without any subsequent issues.

Here are some basics regarding the house. It is a ranch with a roof that spans between exterior walls. There is an interior bearing wall down the middle of the house, so there are three total (2 exterior and 1 interior). The largest cracks were step cracks on the interior wall, and they were no greater than 1/8".

My bet is that the house settled slightly and instantly. I would like to know if there are any opinions as to what may have caused instantaneous settling. A follow up is whether or not this is something that could cause settling in the future, or if it is most likely a one time thing. There was no previous indication of settling ever happening and the house was built in the 50s.

 

[oldestguy]

As with many initial posts, you also are leaving out information. Is there a basement? How was the well installed, specifically was there any drilling to remove soil before casing is "driven". How was it driven? Depth of casing? How deep a well? How far from nearest foundation? Approximate part of what country? General soil types in the area. What climate type? Any trees near the house? Any neighbors with problems? What is meant by your "25 feet"? Any outside ground settling? Any depression at the well? Depth to ground water?

 

[GeoPaveTraffic]

To add to what oldestguy asked, did the drillers use air to extend the well and about how deep is bedrock?

Mike Lambert

 

[WiSEiwish]

I'm not a geotechnical engineer, so I was not aware that all of that info would be required for a general idea a to what may be the issue here. My basic question was can well driving cause instantaneous foundation settlement, and if so, could it start a chronic issue.
Here are some basic answers to your questions:
1. There is a basement - the CMU walls I refer to are basement walls.
2. I do not know if there was drilling to remove soils. The well was hammered.
3. It's about 20ft from the nearest foundation wall.
4. I don't know the depth of the casing or the depth of the well.
5. Southeast Wisconsin.
6. No idea as to the soils type.
7. There are two decently large pine trees and one red maple within about 30ft of the well.
8. Haven't heard anything from the neighbors regarding problems.
9. They were hammering the well and when it was approximately 25ft down the problems started happening.
10. Haven't noticed outside ground settling outside of the fill mound of dirt shrinking a bit.
11. Do not know depth to ground water.

 

[Ron]

Is there any history of subsurface cavities in your area? Have there been sinkholes in the area before? Seems odd that only that amount of activity created immediate settlement, unless a cavity was hit and soil moved from beneath your foundation into the cavity.

 

[GeoPaveTraffic]

While I doubt this is likely to be a continuing problem, it could be. You really need to try and figure out what caused the settlement and that is going to require a local geotechnical engineer who can visit your site and talk with the drillers. You need to find someone who has been around for a long time and knows the area.

Sorry, but there are just too many could be this and could be that items with a situation like this.

Best of luck.

Mike Lambert

 

[WiSEiwish]

Thanks. A local engineer makes a lot of sense to me. I just found it very odd that it happened and that there was no evidence of settlement ever being a problem at the house.

 

[oldestguy]

Apparently only the vibration of the well work, along with an earlier situation of support loss, now seems to be the situation. Erosion due to the well work taking out more soil than required seems not likely now.

I'm from Wisconsin and have seen problems with soil shrinkage that later showed itself with sudden cracks forming, etc. The trees nearby some times were taking water from clay soils. More severe problems like this are farther north, in the Fox River valley (Green Bay area) and near lake Superior. However, the silty clay final deposition over last stage glacial soils (from wind blown silt) does have some potential for this situation in most of the state. That shallower final layer varies in thickness from 10 feet in south west to only 5 feet or so east. However, to blame the problem on shrinkage is unlikely due to the basement excavation requirement which likely went below that clay. An exception may be present locally. This tree moisture demand has seen itself as the cause many times in south part of Wisconsin.

Other than the above possibility, it would seem that some site condition, such as a looser, disturbed zone in original construction, erosion of soil from under a building due to sump pump removal of water collected there, would be what I would look for. To have this happen so long after construction, I'd tend to look at more recent events, such as the sump pump effect. Have there been any sewer damage situations in the last few years? Could the site have been a former quarry or gravel pit, later filled?

If a local geotech is involved, I'd ask if he/she has had experience with clay shrinkage problems. They don't teach this in class.

A "topog map" of the main floor and basement floor elevations might point you toward the area of most effect from what ever is the cause.

Collapse of cavities in rock is unlikely, but not totally so. That's a common S.W. Wisconsin problem.

 

[WiSEiwish]

I haven't been here that long, but my understanding is that the neighborhood used to be a farm. I've been told that a nearby house was actually a farm building at one point. I have not heard of any sewer issues, but, like I said, I haven't been here that long.

Thank you for your input.

 

[oldestguy]

OG here again. I am scratching this old head trying to figure a cause. Another cause could be cinder fill. Years ago cinders were used as a form of "granular" fill, and of course also disposed of. For some reason cinders decompose forever. If the basement area perhaps was muddy at time of construction or for some other reason, a layer of cinders was placed, that might explain it.

In answer to the question, "Is this an on-going threat?", keeping a record of what is happening helps in those cases. At wall cracks draw a light line across it just over 2 inches long. Place cross marks 2 Inches apart. Record length between marks has well as displacement periodically.

For mapping floor elevations use a garden hose fitted with clear plastic tubes on each end (get the fittings at hardware store). Or use a clear plastic hose to begin with. Fill hose with water and flush out air. Place tubes side by side to be sure water levels are same. Use this form of level to record differences in floor elevation at representative places against a more permanent bench mark elevation. This is useful to see effects of current settlement as well as keeping a record with time.

To see if there are any cavities under floor slab, hammer blows on floor are useful. Even light ones tell a lot. Varying pitch of sound is what you listen for. Cavity has lower pitch.

 

[L0k]

My logic is well installed at sand stratum, while drilling may be withdrawn lots of water that reduced the water level.
This sudden draw-down create a certain settlement and cracks.

 

[darthsoilsguy2]

maybe you tapped into an old foundation drain that clogged a long time ago

 

[oldestguy]

OG again: Two questions. Why a well replacement? What does the well log show (DNR gets that log)?

Last summer was quite dry. I am suspicious of soil drying and shrinkage.

 

[dicksewerrat]

Check with the WIDOT. they have been doing lots of bridge work on I-90 and some on that spur that runs to Milwaukee from the Beloit area, I-45 I think.. They may have some good soil logs. Getting one or two east of you and the same west would help.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[oldestguy]

OG here.

If you have time go to the WEB site for Wisconsin Geologic and Natural History.

http://wgnhs.uwex.edu/

Click on Maps. Then scroll through maps and find your county for soil types. I found Waukesah county on second page. These are pedologic soil maps that give a pretty good idea of what is under the area. These are free downloads. Do a "view all maps". The map symbols can then be taken to the profiles in the borders. For instance Miami silt Loam is a common type and more detailed descriptions of these soil series, developed on that wind blown silt (now silty clay) layer can be found by more searches. From these upper 4 feet of descriptions we usually can tell a lot as to what goes on.

 

[WiSEiwish]

Thanks for the info, I'll have time to take a look at it yet tonight.

The new well was installed because the old casing had corroded which they found when they were trying to replace the pump. Basically everything got worse till it was all broken, then they broke it some more. If you can imagine a worst case scenario this was it. At least now the well and pump are both new and work!

 

[dicksewerrat]

I had a well put in near Duluth, MN. My well driller put in a 5 inch casing. I asked why. He said 100 years from now someone can still get the 4 inch pump out. you still need to call the well driller and get the shaft depth and casing depth.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com