Looking for a little help or opinion here. My brother has a slab on grade house that has "settled" over 3 inches during the past year. It began in the interior of the house and has, just over the past couple of months, begun to settle in other areas (ie front porch, sidewalk, etc) Insurance co. is pretty much saying it is not a sinkhole (he has sinkhole insurance). Borings were not done directly over the worst areas as they are in the interior of the house. A boring was done down to around 15 feet to bedrock just outside of the house. Not surprisingly, the low bidder did the work. And we're not talking low bidder by 1k or 2k, but by several thousand (red flag in our minds). My question, being totally ignorant of soil mechanics/dynamics among other things, is this (well several, actually): What is a proper test to determine whether or not the problem is a sinkhole or not? Is 3+" of "settling" realistic" House is 15+ years old, one level, located just south of B'ham, AL. It was a very dry summer last year. We were probably 16-20 inches short normal rainfall. Anyway, I'm probably not providing enough of the puzzle, so I apologize in advance. Any advice is appreciated. Thanks.
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House Settling 3+ inches 1
- Thread starter caravoy
- Start date
caravoy,
This is a complicated question that is incredibly difficult to answer without seeing the site.
For example, my mother in law had similar problems but as I was in a different country I had to rely on her local expert to give her advice. Even though I had been involved in this type of work previously I was no use to her at all without seeing the site.
Have they had a structural/civil/geotechnical engineer investigate the site? If not then who specified the fix? What did they recommend?
If it started on the inside of the house then I would supect that it could be a pipe leaking under the foundations. Was a pipe survey carried out?
As it is after a dry period, it may not actually be that your house is sinking, but that the surrounding soil is swelling again as it has absorbed moisture(and the soil under the footing is still dry).
I would specifically recommend against supporting only part of the house on the bedrock if this is what is planned. This can cause even worse problems if the remainder is still on soil and continues to settle.
It is a pity that it is so far along, because I would really recommend that your brother doesnt get the work done until someone knowledgable is sure that it will fix the problem.
This is a complicated question that is incredibly difficult to answer without seeing the site.
For example, my mother in law had similar problems but as I was in a different country I had to rely on her local expert to give her advice. Even though I had been involved in this type of work previously I was no use to her at all without seeing the site.
Have they had a structural/civil/geotechnical engineer investigate the site? If not then who specified the fix? What did they recommend?
If it started on the inside of the house then I would supect that it could be a pipe leaking under the foundations. Was a pipe survey carried out?
As it is after a dry period, it may not actually be that your house is sinking, but that the surrounding soil is swelling again as it has absorbed moisture(and the soil under the footing is still dry).
I would specifically recommend against supporting only part of the house on the bedrock if this is what is planned. This can cause even worse problems if the remainder is still on soil and continues to settle.
It is a pity that it is so far along, because I would really recommend that your brother doesnt get the work done until someone knowledgable is sure that it will fix the problem.
- Thread starter
- #4
frv, thanks I've cross-posted on the geotech forum. The more the merrier 
csd72,
I'm going from bad memory on some of this, so I may not have the answers, but here goes:
1) An engineer did go out to the site and did some work and a report was created (nice and vague, huh?)
2) A fix, to the best of my knowledge, has not been discussed in-depth (no pun intended)
3) I don't remember hearing anything about a pipe survey or the possibility of a leaking pipe. Good point.
4) The problem began right in the middle of the drought, not afterward (this is when most of the settling occured)
You're absolutely right about the eventual fix. Whatever the fix is (helical piles, grout)etc, it will be done right. No partial support will be tolerated.
Thanks.
csd72,
I'm going from bad memory on some of this, so I may not have the answers, but here goes:
1) An engineer did go out to the site and did some work and a report was created (nice and vague, huh?)
2) A fix, to the best of my knowledge, has not been discussed in-depth (no pun intended)
3) I don't remember hearing anything about a pipe survey or the possibility of a leaking pipe. Good point.
4) The problem began right in the middle of the drought, not afterward (this is when most of the settling occured)
You're absolutely right about the eventual fix. Whatever the fix is (helical piles, grout)etc, it will be done right. No partial support will be tolerated.
Thanks.
i pretty sure that's a karstic area (geologic conditions solutionize leaving voids--sinkholes) but i've never personally worked there. in my opinion, one boring to 15' isn't going to tell you much about karst formations that might (or might not) exist. i don't deal with karst geologies much so i'll leave detailed discussion about it to those that work a fair amount in such conditions. you might check with neighbors to see if they are experiencing similar conditions. it might be sinkholes trying to form or it could be shotty construction or poor foundation conditions.
there's some geophysical explorations that can be used to look for karst formations but it won't be real cheap and it may not yield any answers. i'm not sure how that kind of insurance works but if it does provide indication of sinkholes, i'm guessing it'd pay for itself. i can pass along some information if interested. as far as drilling to identify such conditions, sometimes it's a coin toss as to whether you obtain relevant information.
there's some geophysical explorations that can be used to look for karst formations but it won't be real cheap and it may not yield any answers. i'm not sure how that kind of insurance works but if it does provide indication of sinkholes, i'm guessing it'd pay for itself. i can pass along some information if interested. as far as drilling to identify such conditions, sometimes it's a coin toss as to whether you obtain relevant information.
concretemasonry
Structural
You do not always assume that a structure has settled when there is a problem.
All you should be concerned with is differential settlement. Roads routinely settle or rise far more than that without a problem because there is relaitvely no differential settlement. Your brother needs a thorough professional analaysis of the site to determine the cause and what the possiblr remediation measures are.
All you should be concerned with is differential settlement. Roads routinely settle or rise far more than that without a problem because there is relaitvely no differential settlement. Your brother needs a thorough professional analaysis of the site to determine the cause and what the possiblr remediation measures are.
Yea, obviously you're going to need a professional out there, but from a vague internet point of view and from living in a karst area my initial thoughts point to a lack of soil compaction. Could have been a large area that should have been undercut. Second possibility could be fat clays that are drying out and shrinking. Third and least likely would be a sinkhole since sinkhole formation accelerates as more water is put into it. Since you're in a drought, I'd doubt its that.
msquared48
Structural
Might get some more ideas by posting this thread in the Geotechnical area under Foundation Engineering.
The lowered water table is highly suspect to me. Has the area seen a draught of this magnitude in the past 15 years?
Mike McCann
McCann Engineering
The lowered water table is highly suspect to me. Has the area seen a draught of this magnitude in the past 15 years?
Mike McCann
McCann Engineering
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1
- #9
If the house is 15 years old and the problem has only appeared in the last year, it does suggest that it has been caused by some occurence during or just prior to the last year. As has been suggested this is most likely due to the drought and subsequent 'shrinking' on the subsoil.
I've carried out a number of building investigations for problems of this kind, but have never seen a settlement of 3" (75mm) in a slab on grade. (in Ireland, we don't experience the same degree of variation in our Climate - yet!) The settlements I've seen, of slabs on grade, have generally been due to poor compaction of the hardcore beneath.
Reading between the lines, it seems that the house foundations have not shown the same signs of movement - is this the case? This also suggest that the slab movement is due to soil shrinkage - more pronounced in upper soil layers. How deep are the founds?
If a sinkhole were to develop, I'd expect to see signs of foundation movement - e.g. cracking in supporting walls.
Check out the attached reports.
I've carried out a number of building investigations for problems of this kind, but have never seen a settlement of 3" (75mm) in a slab on grade. (in Ireland, we don't experience the same degree of variation in our Climate - yet!) The settlements I've seen, of slabs on grade, have generally been due to poor compaction of the hardcore beneath.
Reading between the lines, it seems that the house foundations have not shown the same signs of movement - is this the case? This also suggest that the slab movement is due to soil shrinkage - more pronounced in upper soil layers. How deep are the founds?
If a sinkhole were to develop, I'd expect to see signs of foundation movement - e.g. cracking in supporting walls.
Check out the attached reports.
- Thread starter
- #10
Thanks for all your replies.
Mike, I tried to post in geotech forum, but somehow it has been deleted. Not happy about that. Last summer was pretty bad, but I would be surprised if it was that order of magnitude worse than any other year over the past 15. Of course, maybe it was that little extra dryness that did it. Everything's decided at the margins, huh?
renko, I believe it is correct that the foundations are not seeing movement. I need to double-check that, however. Couldn't speak to foundation depth, though I'd guess less than 24 inches around the edges. Fortunately, not much problems with frost line down here.
Thanks again.
Mike, I tried to post in geotech forum, but somehow it has been deleted. Not happy about that. Last summer was pretty bad, but I would be surprised if it was that order of magnitude worse than any other year over the past 15. Of course, maybe it was that little extra dryness that did it. Everything's decided at the margins, huh?
renko, I believe it is correct that the foundations are not seeing movement. I need to double-check that, however. Couldn't speak to foundation depth, though I'd guess less than 24 inches around the edges. Fortunately, not much problems with frost line down here.
Thanks again.
caravoy,
It sounds to me like something has happened recently to cause this, something along the lines of a leaking pipe.
You generally dont get a stable building start to subside without a root cause.
But without knowing what the report said, it is impossible to make an informed comment.
Can you get a photocopy of the report, delete out all specifics on company, adress e.t.c. and then post it on the forum. We then can hopefully make a more informed comment.
It sounds to me like something has happened recently to cause this, something along the lines of a leaking pipe.
You generally dont get a stable building start to subside without a root cause.
But without knowing what the report said, it is impossible to make an informed comment.
Can you get a photocopy of the report, delete out all specifics on company, adress e.t.c. and then post it on the forum. We then can hopefully make a more informed comment.
- Thread starter
- #13
csd72,
I'll see what I can do about posting the report.
renko,
Thanks for the link.
By the way, why would my post have been deleted over at the geotech forum? Is that improper or something? It was there for a short while after I reworded the subject line, then it disappeared. Without an explanation, that made me a bit angry.
Thanks again.
I'll see what I can do about posting the report.
renko,
Thanks for the link.
By the way, why would my post have been deleted over at the geotech forum? Is that improper or something? It was there for a short while after I reworded the subject line, then it disappeared. Without an explanation, that made me a bit angry.
Thanks again.
msquared48
Structural
caravoy:
If it appears that your post is for a personal project rather than a professional problem, the post stands a high likelihood of being deleted in most any forum here. Justr follow the lead of csd72 and it should remain.
Mike McCann
McCann Engineering
If it appears that your post is for a personal project rather than a professional problem, the post stands a high likelihood of being deleted in most any forum here. Justr follow the lead of csd72 and it should remain.
Mike McCann
McCann Engineering
- Thread starter
- #15
Well, it was deleted again. I know I'm whining here, but isn't it a bit of a gray area to be that restictive about what's deserving of posting or not? I mean, if I can't ask professionals for advice about a subject directly related to their profession, personal or not, then should I just deceive everyone and say something like, "My client yada yada yada..." and then ask the question, instead of "My brother blah, blah, blah..." At the minimum, an explanatory email would have been nice. Oh well, guess I'm just being thin-skinned.
Everyone here has been very helpful, and I appreciate it. I'll see if I can get that report so I'm "legal"
Everyone here has been very helpful, and I appreciate it. I'll see if I can get that report so I'm "legal"
civilperson
Structural
Duplicate postings are prohibited and deleted.
msquared48
Structural
OK... considering civilperson's post, ...
Try rewording and changing the layout of the post from the beginning then, and see if that flies, with csd72's recommendations too.
Mike McCann
McCann Engineering
Try rewording and changing the layout of the post from the beginning then, and see if that flies, with csd72's recommendations too.
Mike McCann
McCann Engineering
I actually replied to your other post before it was deleted, and think it probably disappeared because someone reported you for cross posting.
I had agreed with some others here that the first thing I would consider was shrinkage of moisture sensitive clay. Are there large trees around which could have stolen the moisture?
But my opinion was based on the house being on a slab foundation, rather than with separate footings and infill slabs. Settlement of the slab relative to the footings would tend more to the idea of loss of ground under the slab. Where it could have gone is not for guessing, but for investigation.
I had agreed with some others here that the first thing I would consider was shrinkage of moisture sensitive clay. Are there large trees around which could have stolen the moisture?
But my opinion was based on the house being on a slab foundation, rather than with separate footings and infill slabs. Settlement of the slab relative to the footings would tend more to the idea of loss of ground under the slab. Where it could have gone is not for guessing, but for investigation.
I had a quick look for the forum 'rules' but couldn't find them, however, I believe the intent of the forum is for discussion between professionals within their discipline(s).
Technically this would rule out mechanical engineers asking for advice about their personal structural problems.
Personally I don't have an issue with your question and the moderators for this structural forum seem to feel the same way; our geotech friends may not agree.
Technically this would rule out mechanical engineers asking for advice about their personal structural problems.
Personally I don't have an issue with your question and the moderators for this structural forum seem to feel the same way; our geotech friends may not agree.
- Thread starter
- #20
Thanks, hokie66.
There are a couple of trees of size around, but assuming a root ball equal in size to the spread of the tree, they don't come within ten+ feet of the house. I'm curious what trees can do in a situation like this. Please explain.
As to the construction, and this is prime example of my limited knowledge and info, I believe it is a slab foundation, and not separate footings with infill slabs. My response to renko probably caused the confusion here. Looking at typical construction drawings for slab-on-grade, I notice that the perimeter is thicker than the main interior slab. This is the region I was referring to as not being more than 24 inches below grade. I guess it's possible that it could be a 4" (or whatever) thick slab everywhere. The sample drawings I've seen had the "integral" footings.
Thanks.
There are a couple of trees of size around, but assuming a root ball equal in size to the spread of the tree, they don't come within ten+ feet of the house. I'm curious what trees can do in a situation like this. Please explain.
As to the construction, and this is prime example of my limited knowledge and info, I believe it is a slab foundation, and not separate footings with infill slabs. My response to renko probably caused the confusion here. Looking at typical construction drawings for slab-on-grade, I notice that the perimeter is thicker than the main interior slab. This is the region I was referring to as not being more than 24 inches below grade. I guess it's possible that it could be a 4" (or whatever) thick slab everywhere. The sample drawings I've seen had the "integral" footings.
Thanks.
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