Home Front by Don R. Carter PE
The day the house fell
The Day the House Fell1 is the title of a book by Richard Handy, wherein he states, “About half the houses built every year in the U.S. are founded on expansive clays. Half of those will eventually show some distress. Of the houses with expansive clay problems, chances are 1 in 5 that the house will become seriously affected.”
USDA maps show that 60 percent of Johnson County soil types are expansive clays, so if I’m doing the math correctly, that means that 1 house in 17 will have foundation problems. If this seems high, look in the Yellow Pages; you’ll find nearly 80 companies offering foundation repairs. Someone is keeping them in business.
The previous “Home Front” presented basement wall repair options, and in this issue we discuss realigning a crooked house. If you have sheet rock or plaster cracks, doors that stick, uneven floors, windows that won’t open, or basement wall splits, these are classic signs of a misaligned house. Misalignment can come from settlement or heave; either way, the cause is probably expansive clay soils rearranging your footings. Here are the popular systems used to correct settlement:
Underpinning. This method uses drilled or hand-dug holes positioned beneath the foundation footing. The depth of the hole is subjective, but the goal is to go deep enough to get past expansive clay and into sound soil. The hole is then filled with concrete to produce a pedestal from which jacks and shims lift and hold the house. It’s an old concept, with nearly 100 years of mixed history.
Helical piles. These are the screw-in devices shown in the last issue as tension tiebacks. They also work in compression, and can be screwed into the soil to a predefined torque, then used as jacking platforms. They work in lightweight structures where push piers won’t.
Auger piles. Sometimes called mini-piles, auger piles are made by drilling small-diameter holes under footings and filling them with steel and grout. Similar to underpinnings,they are smaller and thus more of them are required.
Pre-cast cylinders. This system works by pushing precast concrete cylinders into the ground to refusal. To make sure cylinders stay in line, a steel cable is strung through them, somewhat like beads in a necklace. Once in place, cylinders get a jacking pedestal on top and the house is lifted from that. There are mixed results with this system.
Push piers. This relatively new system uses a hydraulic jack stand and the home’s own weight to push steel tubes into the ground. Think of a bumper jack without a base plate. Instead of the house going up, the jack shaft goes down, penetrating into the ground. I put five push piers under my house in 1990 and they have held well. Push pier advantages are certified product capacity (required by some cities), reduced secondary damage to landscaping, and faster turnaround.
Each system has one thing in common: They are only as good as the person who installs them. Do your homework, as there are a lot of pretenders in the foundation
repair business. If you need a tiebreaker, call one of the several engineering companies that specialize in foundations.
1 The Day the House Fell, by Richard L. Handy, PhD, © 1995, ASCE.
