Posted May 16, 2016
Why We Do Not Recommend Installing Wall Anchors in Expansive Clay Soils
A nearly 10 year old study commissioned by the City of Menasha, Wisconsin points out some of the challenges inherent in the wall anchor method of repairing bowed basement walls in expansive clay soils, specifying among other things that anchor systems should be installed below the frost line (which naturally varies from season to season and can extend below the footing of a shallow foundation home that is 4 to 5 foot deep).
The concerns raised in this report have not altered the behaviors of most companies in the foundation repair business who continue to install anchors and tension systems without site specific engineering or soil reports to back their work.
As the owner of Basement Repair Specialists, a contracting company with offices in Appleton, WI and Lake Elmo, MN that repairs failing foundations, I can verify that every year we re-repair foundations, often wall anchors installed in unfavorable soil types that have failed, notwithstanding the thousands or tens of thousands of dollars homeowners have invested in these failed attempts. I won’t even begin to approach the ethical implications of this.
As a company, Basement Repair Specialists does not advocate nor will we install wall anchors or other tension systems in the highly to very highly expansive clay soils we have in Wisconsin. These systems are an inferior option to removing and replacing faulty backfill soils next to the foundation, which are the source of the problem. It should be obvious that anchoring a wall to the soil that is moving and causing the failed wall in the first place is not the best way to address lateral pressures on a wall. In addition, such repairs do nothing to address exterior water conditions which can be brought indoors by holes penetrating the wall to allow for the anchors to be installed.
Generally speaking a bowed wall is the result of lateral inward pressure on the wall. Depending on type and drainage, particularly when they have a high linear extensibility rating, soils can exert substantial pressure on basement walls due to among other things frost heave and thaw cycles, saturation and desaturation of soils, and the expansive characteristics of the soil itself.
These soil conditions can easily exert forces in excess of a concrete wall’s ability to withstand. A study by the City of Amherst NY at http://www.amherst.ny.us/pdf/building/soilsstudy/TOASFS_section3.pdf discusses the problems related to improper backfill and how prevalent are foundation failures due to simple errors during the construction of houses, and how poor backfill conditions can provide situations where lateral soil loads actually exceed a wall’s theoretical design strength (ability to handle the horizontal load applied to the wall due to soil expansion).
Many contractors prefer to install wall anchor systems since they do not require excavation and are less costly to install. A wall anchor system avoids the investment involved with removing truckloads of faulty soils and properly disposing of them, then backfilling with many tons of aggregate to prevent lateral loads in the future. But a foundation repair contractor’s profitability model is not a good reason to implement an inadequate repair that stands a chance of failure in the future. Any basement wall repair that requires continued bolt tightening by the homeowner to keep in force its warranty should be viewed with considerable skepticism. A wonderfully succinct and unbiased webpage is at https://www.fairfaxcounty.gov/landdevelopment/sites/landdevelopment/files/assets/documents/pdf/publications/marine_clay_guide.pdf and tellingly excludes any mention of wall anchors as a repair method for bowing basement walls in expansive clay soils. There are some additional great tips for avoiding the problem in the first place such as proper grading and extension of downspouts.
Where soil types are questionable or poor, the best way to prevent further damage is to remove the offending soil, ensure proper drain tile installation, and backfill with clean stone– all of which ensures lateral loads on the walls are well below stress levels that could move the wall. Then, structural supports can be added, yielding a result that is stronger than a newly constructed wall.