# Foundation Lifting ???????



## Chris Johnson (Apr 19, 2007)

I haven't had to deal with shale yet, mostly sand or expansive clay. Any reason why a structural slab would not have worked here? or a post-tension slab?


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## woodchuck2 (Feb 27, 2008)

I saw this similar thing happen at the Fire dept. i was a member of. The sidewalk in front of the building had heaved up about 12" over the yrs and it was pushing up the the posts supporting the front overhang. Every year we had to jack up the over hang, cut off the posts and set it back down to level. Now the building sits at the base of a mountain and it too had to blasted for the building to be built and it now sits on a slab. The Town had installed storm drains in front and to the sides of the building but there did not seem to be a lot of water shed from around the building. We had a local fella come in and pull the sidewalk out and he hit some water, he then scraped along the front of the slab pulling some of the excess concrete with it and the water shot out like from a broken pipe. It drained like this for several minutes but overall it took several hours for it to drain down to a trickle. Apparently the slab was holding the water back and was keeping the water under itself causing parts of the building to heave and move. The contractor redid all the drainage around the building, he tore up the whole lot in front of the building and he got a variance to take up part of the road as it too was buckled. With the help of the County highway he was able to put in oversize drainage and tie it all in with the Town drainage. Since then we have had no issues but the drainage runs yr round through the culverts. Amazing what hydaulic water pressure can do.


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## concanoe1953 (Apr 24, 2011)

Did a foundation repair on a full basement built on clay where the doors didn't open and in some cases close, cracked drywall, etc. All of the evidence pointed to a series of 6" X 6" wood columns in an interior wall that supported the floor joist system of the first floor. The shale was taking on water and lifting the 2'X2' spread footings, which in turn were lifting the solid wood columns. the weight of the perimeter of the structure had adequate weight to offset the lifting expansive shale. I solved the problem by using temporary shoring so that the wood piers and spread footings could be removed. 
I then replaced the spread footings with 8" in diameter drilled piers that I isolated from the slab. I then replaced the wood columns with 3" adjustable steel columns. We removed the slab, excavated the shale for 6" with drainage to the soil surface, placed the layer of compacted granular material, and provided a drainage outlet so the expansive soil doesn't reach saturation, and then replaced the floor.
By going deep with piers to allow the end bearing and friction surface of the piers to carry the load, the thin layer of soil that was swelling could no longer lift the columns as they had the spread footings on the soil surface.
The drainage system under the slab limited the expansion of the shale by limiting the water that was held under the slab. this controlled the heaving potential of the slab.
Did the repair in the early 90's and it's still doing the job.
Send a soil sample to a geotechnical engineer to verify the swelling potential of the soil before you start.


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