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Repairing a Foundaton When Space, Time and Cost are Issues
Note: This is a reprint of an article originally published by Constructor Magazine
On previous jobs, we believed post-tension slabs would be enough to sustain a new foundation until a geotechnical engineer could do a proper soil reading. However, after consulting with the geotechnical engineer about the condition of the surrounding soil, we knew slabs alone wouldn’t do the trick, and neither over excavating nor employing water remediation to the surrounding soil was a feasible solution.
Bad soil is the main factor that affects foundations. Contaminated dirt and expansive clay weaken structural support over time, while clay soil leads to foundation cracking in the years following installation. Plus, when excavating contaminated soil is possible, it’s an expensive alternative.
Anticipating these flaws and building them into the blueprint of your structure puts your building ahead of the game and prevents engineers and contractors from continually having to invest in repairs as time passes.
Foundation fixes and when to use them
When it comes to repairing the weakened base of a structure, contractors often employ one of three methods, though each carries its own set of flaws:
- Cylinders/cable locks: When installing these in concrete, it is extremely difficult to penetrate with enough depth to enter the soil’s active zone. This limits a contractor’s ability to verify he has a solid, connected pile below the structure.
- Soil and grout injections: Aside from monitoring pressure, there’s no real way to discern whether this is viable long term. Settling is a real concern with injected materials, and this could lead to an inadequate shoring up of the soils; because grout is injected under pressure, it can inadvertently fill drain tiles and sewer lines or flow into void spaces.
- Concrete drilled piers: These pieces are filled on-site and add several days to the installation process because the concrete needs to properly cure. It is difficult to make sure drilled piers are installed deep enough, meaning uplift brought on by expansive soil is a real possibility. Implementing these piers requires large machines, which can damage lawns and landscaping.
How to find the best solution
The best repair options for your building hinge on many things. Minor slab repairs may require something as simple as soil injections for aesthetic purposes.
If a foundation needs to be lifted for any reason, contractors may need to use piles, concrete, helical, push piers, or other deep foundation methods. To further evaluate the jobsite, take these four steps to determine the best repair option:
1. Evaluate the soil. Read the geotechnical report to determine whether the soil is stable enough to support a structure long term or past the length of the warranty. If there is no current report, contact a geotechnical engineer to order a soil boring or probe.
Identify active zones, and determine whether water tables or wet material are present within the soil. This will have a major impact on your pile design and needs.
2. Consider your surroundings. If there are other homes or structures in the area, consider noise pollution in your repair decisions. Vibrations and other possible property disruption concerns should be addressed before finalizing any solutions.
Helical piles help repairs located in hard-to-access areas and are typically installed with skid-steer loaders, rubber-tired backhoes, and mini-excavators. Due to their small stature, these machines function better in harder-to-access areas and don’t do as much damage to surrounding areas.
3. Look at the time commitment. How much time does the foundation solution require? Using concrete requires several days of on-site curing, meaning owners must deal with the mess of construction for a longer time.
Then, there is the question of whether the supplier will deliver the materials to the site within the agreed-upon time frame. Will there be additional costs or surcharges for on-site delivery? For instance, helical piles are premanufactured and can be loaded immediately after installation.
This option has obvious benefits, most notably that owners aren’t inconvenienced for longer stretches of time. It can also lead to a lower chance of cost overrun or other issues.
4. Research product quality. It is important to select a brand that has a history of expertise. Utilize products with the Certified Manufacturing Inc. seal, which are made in the USA, are building code-approved, and contain a product and/or installation warranty. Find a product manufacturer able to meet or exceed these qualifications to avoid concerns in the future.
Repairing a structure’s foundation should not be a hassle for anyone involved. With the right product, it can be a painless process that sets your structure’s foundation up for a healthy, stable future.
Gary L. Seider, P.E., is engineering manager of CHANCE® Civil and Utility Helical Products. Hubbell Power Systems Inc.manufactures a wide array of transmission, distribution, substation, OEM, and telecommunication products used by utilities.
With four U.S. patents and more than 40 years of industry experience, Seider oversees the company’s civil construction and utility application/project engineering staff. His team assists owners, engineers, and contractors with technical assistance, guidance, and recommendations for the proper use of CHANCE Helical Anchors and piles and Atlas Resistance® products.
by Gary L. Seider