Due to the recent earthquake and resulting damage, many homes have foundations that have settled and suffered other damage. Below, I hope to explain how helical piers can successfully repair these foundations and briefly touch on other repair methods.
First, we need to understand what happened:
In many cases the ground underneath the foundations settled during the earthquake and the two main likley culprits are:
(1) Soil liquefaction – which occurs when a saturated or partially saturated soil substantially loses strength and stiffness in response to an applied stress such as shaking during an earthquake or other sudden change in stress condition, in which material that is ordinarily a solid behaves like a liquid.
(2) Improper and/or inadequate footing preparation or placement of ‘man-made’ fill during the original construction.
How helical piers resolve this issue and prevent future settling.
Helical piers are steel piles that are driven deep into undisturbed soils and are considered a “deep foundation”. Simply put, they are drilled deep into the ground through disturbed or weaker soils into denser, deeper soils which are better able to support the weight of the structure above.
We have the ability to run our helical piers deep into competent soils, passing through weaker soils; such as peat, soft clay and other soils that are subject to failure under weight or in events such as earthquakes. The installation into these soils allows the piers to hold heavy loads; such as a house. The installation process is engineered; meaning that when we install the piers we know the exact weight the pier can hold in that soil. If we need the pier to hold more weight, we simply install the helical piers deeper into denser soils.
The whole idea behind helical piers is to bypass that weaker soil and find deeper denser soils to hold the weight.
Techno Metal Post has almost 10,000 helical piers installed throughout the Anchorage and Mat-Su area and have had no reports of failures. In fact, this fall we recently re-supported a house foundation that had settled from the previous earthquake two years ago. We found almost 10′ of peat soils on this lot near Minnesota Drive and International – the same place we saw the dramatic failure of the Minnesota off ramp.
Scroll through the below gallery to see the repair process for this house:
How did our helical piers do in the Earthquake on November 30, 2018?
After the earthquake, we went back and took elevation measurements to determine if the house had settled. We found that the house’s foundation remained level and did not suffer any settlement during the quake. We have also checked similar projects and have seen the same result: structures supported by our helical piers were not affected by the quake and remained the same as the day they were installed.
What do we know about helical piers and earthquakes?
Until recently helical piers have not undergone extensive testing during seismic events. That changed when the University of Oklahoma’s Amy Cerato PhD, PE decided to study and test the performance of helical piers (under load) in earthquakes.
A link to her blog and study can be found here.
And we also wrote a bit about earthquakes after we endured the January 24, 2016 quake which was felt throughout Southcentral Alaska. At that time, TMP AK also inspected many houses supported by our helical piers and found similar results – no damage and no movement of the piers.
Through testing and ‘real world’ events, Dr Cerato’s hypothesis remains true:
“The international community has qualitative proof that helical piles perform well in earthquake prone areas”
What other methods are used to repair failed foundations? Do they work as well as helical piers?
Helical Piers are not the only method used to lift and stabilize houses. Other methods include:
* Slab Jacking – Where a concrete slab (or foundation footer) is lifted by injecting a concrete mix under the slab until it lifts the slab back level.
* Foam Jacking – Where foam is used in place of the concrete mix.
* Excavation-based Repairs – Where various methods are used to excavate the materials under the failed foundation and replace them with gravel, concrete or wider footers to support the weight of the structure.
The downside of each of these repairs is that they do not address the underlying cause of the original foundation failure – that the soils do not want to hold the weight of the structure. The above methods are reliant on the idea that the soils will not settle again and do nothing to solve the original problem.
In fact, we have many cases where we have seen failures of the above methods.
One example occurred in Anchorage where a contractor was called to fix a house that had settled 6″. Their “fix” was to excavate below the existing foundation, use jacks to level the house and create a new (much larger) and deeper footer to support the house. The failure was almost instantaneous, the house sunk about 8″ (more than the original settlement) due to the fact that the soils were not capable of holding the weight of the house, let alone the additional 20,000 lbs. of additional concrete. TMP AK was able to install several helical piers down to 30′ to find soils capable of holding the weight and we lifted the house (again).
Another remarkable example happened during the November 30th earthquake at the house near Minnesota and International Airport in Anchorage — the same house mentioned above that we repaired from previous earthquake damage. We were pleased to learn that it was not the helical piers that failed. It was the foam-jacking that had been used to repair the interior concrete slab portion of the house that suffered the significant failure. Helical piers were used to lift and stabilize the perimeter foundation, and could have been used to support this slab as well, but the lower cost option of foam-jacking was chosen for that section. After the quake, TMP AK returned to the house to check for any failures. When we measured the house, we found that the slab (the part repaired by foam-jacking) had sunk up to 4-5″, while the perimeter supported by helical piers remained in place.
If your home has suffered earthquake-related foundation damage, we hope the information above provides some understanding of how helical piers may be the best choice to repair the damage.