What is Foundation Piering and how does it work?
Today, more and more houses are being built on unstable ground, like the ones you learned about in the previous chapters. Between expansive and hydrocompactable soils and subsidence, the foundations are pushed and pulled creating movement. Every year, thousands of homeowners are faced with evaluating and repairing foundation problems. Fortunately, this means that reliable engineering solutions are available.
What exactly is available and is it the right solution for your structural problems?
Since the root of structural problems is the soil, the first two solutions have to do with taking the weight of the foundation off of unstable soil and placing it on bedrock or other stable soil; these solutions are called thrust pillars and helical pillars.
Thrust springs are basically long steel shafts that are driven hydraulically into the ground through unstable surface soils until they reach bedrock or other load-bearing strata. Technicians can tell that the piers have reached bedrock by measuring the hydraulic pressure required to drive the piers into the ground until they reach the depth specified by the engineer. The weight of the house is then transferred from the unstable soil to the pillars via pillar supports attached to the base of the house.
Coil springs are similarly driven into the ground by hydraulic systems, but are turned in the ground like a giant screw. In fact, they are giant bolts that literally hold up a house through the power of resistance. The weight of the house is then transferred to the pillars using the same durable steel supports.
Indications that you need a drilling system:
You have an area of your foundation wall that is experiencing vertical movement, such as subsidence.
Your chimney is not flush with your house.
Its soil conditions can be classified as expansive, sunken, hydrocompactable, or active.
How springs are installed in 6 basic steps:
Step 1: Outside, the grass and landscaping around the house are removed and set aside.
Step 2: Dirt is removed until the base of the concrete pad is revealed.
Step 3: Heavy industrial-strength steel foundation pier anchor brackets are attached to the house foundation.
Step 4: Strong steel pillars are hydraulically driven into solid bedrock or equally load-bearing strata.
Step 5: The weight of the house, anchored to the steel supports, is carefully transferred from the unstable soil to rock-solid pillars.
Step 6 – After approval by an engineer, the soil around the house is replaced and the landscaping can be returned to its original location.
There are several other options that have been used at different times to solve foundation problems. The older method is to raise the house and replace the foundation, and the newer method is to use pillar systems around the entire perimeter of the house or just part of it. Here’s a breakdown of the other methods people have used to resolve database issues, from oldest to most recent:
Replace Foundation:
Destroys the courtyard and takes several weeks to complete
There is no guarantee against a recurrence of the same problem (expect the same result
Footings are still in the Active Zone
VERY EXPENSIVE-$50,000 PLUS
Concrete foundation/extended foundations:
It can take weeks/months
The added weight of the concrete can make the problem worse.
The structure cannot be lifted
Footings are still in the Active Zone
Concrete piers:
Concrete cylinders can break during installation and CANNOT be recovered due to depth
The cylinders create too much friction on the skin to pass through the active zone
May require additional shims in the future
Even if shim is included in the warranty, damage from resettlement and re-excavation is not covered.
Square axis helical abutments:
Originally designed to provide resistance to guy wires on power pylons during high winds.
Not designed to support weight through floors
Square shafts experience bending and folding when the weight of a foundation rests on them.
Concrete pillars with cable reinforcement:
Designed for specific soil conditions not present in Colorado.
The cylinders create too much friction on the skin to pass through the active zone
The wiring in the center of the pillar stretches over time, allowing for moment after moment on location.
Additional wiring on the outside of the cylinders can increase the surface friction of the cylinder.
Finally, the drilling systems:
Thrust Springs:
Allow the deepest penetration of any type of spring steel.
Allow for the possibility of low-impact interior installations (typically with much less collateral damage than the exterior approach)
Provide a lifetime warranty, transferable for the first 25 years, that there will be no vertical movement in the dock areas.
Get the job done in most ground conditions for a designed service life of 100+ years.
MAY thrust springs:
Allow the probability of raising a structure to a flatter, more level condition
Allow the possibility of closing or reducing existing cracks in brick, stucco, plaster or other interior or exterior finishes.
Allow realignment of glued doors or windows and straightening of sloped chimneys
Thrust Springs DO NOT:
Assurance that perfectly flat or level final conditions will be achieved
Providing lateral (horizontal) restraint to a sloped foundation wall
Improve water tightness or lower the humidity level in a base
coil springs:
Get the job done in most ground conditions for a designed service life of 100+ years.
Allow installation on relatively older, weaker or lighter foundation types
Allow installation as a pre-construction (or new construction) bearing system in poor soils
Allow for horizontal installation as a “tie” system to provide landslide resistance in hillside areas
With some rare exceptions, it requires exterior excavation, with destruction of the surrounding landscape or paving.
Provide a lifetime warranty, transferable for the first 25 years, that no vertical movement will occur in dock areas.
MAY Coil Springs:
Allow the probability of raising a structure to a flatter, more level condition
Allow the possibility of closing or reducing existing cracks in brick, stucco, plaster or other interior or exterior finishes.
Allow realignment of glued doors or windows and straightening of sloped chimneys
Coil springs DO NOT:
Assurance that perfectly flat or level final conditions will be achieved
Provide lateral (horizontal) restraint to a sloped foundation wall (unless specifically installed in “tie” mode)
Improve water tightness or lower the humidity level in a base
