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Northeast Ohio- addition done 2 years ago, ( 24′ x 12′ 3 sides )customer pulled permits and acted as own GC. Backed out wood crawl space for cheaper price to pour slab. Footer dug 42″ below grade,24″ wide, reinforced with rebar and poured to grade. 3 courses of block with L block installed on top course.
Ground not disturbed, only in footer area. fill stone #57 installed in cavity, tamped and reinforced with wire. Some evidence of slab movement within 3 months, yet no movement in out side walls or block. Addition butted up to wood frame construction. Slab has pulled away from existing house about 3/4″. No cracks or physical damage to outside walls of addition.
I paid to have engineer look at problem and he recommends soil or core samples. Price range in the area of $3 to 5 thousand. I cannot afford this was not enough in the job, customer will not pay for it either.
Spoke with building department and he said they had similar problems in that neighborhood with serious ground movement. Engineer said construction practices look good. had inspection on footers and prepour before slab, and passed. Trying to help customer out, she is in a tough situation.
House could have been built over bad earth, looks like addition may have been also. HELP ME, looking for way to work this or suggestions on what to do. Would be glad to answer any questions you throw at me.
My problem ? owners problem? concrete subs problem?
Thank you cc
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You brought your footer to grade, then went up 3 courses of block and poured a slab? What did you pour the slab on? Must be about 20" of some kind of fill. Did you fill in lifts of 6" and compact each lift completely? Or is it all filled with 57 stone? How was the slab terminated at the existing structure? Footer? Thickened edge? Doweled to existing foundation? Is the movement away - horizontally - from the existing structure, or down?
Are you sure it's your slab that moved and not the existing structure? In that light, is the footer of the existing structure up to snuff for the area?
*Yes Ralph, fill was tamped in lifts and placed on existing clay soil that has been there since the house was built 15 years ago. Footers were doweled in to existing block of basement in house and filled.Movement is away and slightly down, but has not pushed out the outside walls.Could be existing footer??Any ideas on how to proceed?One thought I had is to tear out slab, dig sonotubes ( 2 ea.) in center of slab, rebar it out and pour new slab at owners expense.cc
*I wonder whether the clay you speak of under the fill is expansive. Could the problem be that the slab and house addition have kept rain off the clay, and that it has dried-- and therefore shrunk?If this is a potential problem, then you should be able to diagnose it by digging down (outside the foundation!) below any topsoil to the clay strata (where did you hit the clay when you dug the footers?), collecting a small pail of the clay and taking it to a soil lab for analysis. I am skeptical that you need to pay $3K-$5K for a bunch of core samples under the slab in this case.With regard to a fix, I'm out of my depth. IF the problem IS expansive clay that is now drying out, and IF there is a framed enclosure over the slab, then you might break out the slab and give the ground a few seasons to dry out, and then re-pouring. In the St Louis area, most builders frame the house over the basement and garage, and then pour the basement floor much later in the building cycle. That makes the framer's job harder, but gives the clay some time to dry out.Boy, this doesn't sound at all appealing, does it. I would be concerned about attempting mud-jacking or pressure grouting because I'm not sure that the concrete blocks will take the pressure without failing outward. How did you tie them to the footers?
*Here's another option for you. I ran your problem by some people who do major repairs, mudjacking and helical piers and they ventured a guess that since there is no evidence of other exterior damage to walls or foundation that your problem is not the result of the clay soil. Their first guess was an inadequate compaction of fill. Their suggestion was to take some base measurements such as height above known fixed surfaces and incline angles to see what was moving and in which direction and come back later, maybe six months, and see if anything has changed. If nothing has changed, then the slab could be topped and leveled and you're done. If there is change in the slab and there is still no footer, foundation or other movement or damage to the rest of the addition then you could look into an invasive procedure to check under the slab, possibly turning in some piers to supportive soil and then raise the slab to level, fill the holes and be done. That's not cheap. They do not recommend mudjacking. If the soil will not support the slab then it will not support an injection either.Your idea of breaking out the slab and placing supporting piers might work too if you could reach supporting soils. If you don't reach the support and there is a clay soil or other nonsupportive soil condition you are going to have sinking piers as well as a sinking slab.
*sorry. i can't offer no remedy...just some input...watched my father struggle with a jack in the corner of the basement in my youth. helped him with the plumb line and level. it was one of my first lessons in construction. i also watched a retaining wall keel over in the back yard. i was left with the impression that pop had just made mistakes.pop passed on. i went to college. eventually ended up in maintenance and construction.while in college, i learned about a phenomenon termed "creep". clay soils actually ride over inclined bedrock when water saturates the clay.gave me the first clue that pop was maybe fighting a losing battle...twenty years after pop passed on, i'm reading the LA Times and there's a picture of the street that i grew up on! the story... geologists had determined that all the homes in the area had been constructed on clay that was actually part of an ancient landslide!!! pop never had a chance.the homeowners in the community wound up suing the building department. don't know the outcome.brian