You are currently browsing the Rock Solid Restoration LLC Blog weblog archives for April, 2011.
9. April 2011 by admin.
About ten to fifteen years ago helical piers were introduced into the Denver Colorado area as a means of supporting the vertical weight of buildings and other structures. The traditional use of the helical piers had been to tie back structures such as telephone poles in order to stop the poles from falling over which they are very effective at doing. This hold back capability became a main selling points in expansive soils as they were purported to be able to hold the buildings down when the upper soils heaved and tried lift the buildings up. Somewhere along the line it was discovered that a lot of pressure could be applied by pushing on them instead of pulling and with that information the idea to use them as vertical supports was born. They are especially effective in soils that never get really high bearing capacities as the flights at the end can be produced in different sizes and the square inches of bearing can become quite substantial. They screw into the soils and do not need a lot of down pressure to advance which allows their use on light structures. Their holding capacity is calculated by the amount of torque (TWIST) that is applied. Overall they have performed pretty well. If they are seated properly and do not get water infiltration at the tips, they will work.
Like any process they should be installed in areas where they are effective and not installed in areas where they are ineffective. Soils that have a lot of cobbles are a big concern as we have seen that they have a lot of trouble pushing past too many cobbles. The other area that seems to cause some problems is that in expansive soils the bedrock is also expansive. The helical shaft hollows a space out around itself as the pier goes down and this allows water infiltration into the expansive bedrock. If this causes the bedrock to swell, the building will be pushed upward. I think that some of the helical installers have the capacity to gout their columns full length which might alleviate the problem.
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