Impact driven ‘mini-pile’ failure in Anchorage

Earlier this summer we received a phone call from a client who had recently hired a local company to construct a small deck. The deck was supported by 2 impact driven mini piles in very wet clay soils. After the first winter, the clients noticed some heaving. After subsequent years the heaving got worse and worse.

They realized they had a bigger problem with their deck when they noticed the heaving was bending the frame of their sliding glass door. After the clients received no acceptable solutions from the original installer, they contacted Techno Metal Post Alaska. One of the “solutions” offered by the original contractor was to dig around the post and fill that area with gravel; which may have only exacerbated the problem. I was able to make the trip out to view the deck and saw that the 2 3/8″ mini pile had in heaved up over 4 inches.

The mini-piles are just steel posts that are hammered into the ground, they have no ability to withstand uplift from frozen soils. The area of town where this deck was constructed is known to have poor clay soils with a very high water table. In fact, when we cut the tops off the mini piles, I noticed that they were filled with water.

I knew our helical piers could solve the problem. Not only does the helix on our helical piers support compression (downward) loads; it also resists the uplifting forces from heaving soils. That uplifting (or tension loading) is something we have had our posts engineered and tested for. Beyond that, out frost protection sleeve eliminates virtually all contact between the expanding soil and our helical piers. These two reasons make it very easy for us to guarantee that our posts will not heave in freezing soils.

Removing and replacing the 2 mini piles only took a few hours. I only needed to pull the decking back enough to expose the beam. We removed the beam and installed our posts between the deck joists.

After our posts were installed, we installed a new beam and adjusted the height with our adjustable brackets. We reinstalled the decking and righted the deck for our very happy clients. They will never again have to worry about their deck heaving again.

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