Foundation UnderpinningFoundation Repair Article
Foundation Underpinning- Understanding the Types
Foundation underpinning or stabilization can be performed using several foundation repair methods, including piering, wall anchors or mudjacking. Piering can be performed with round shaft piers, square shaft piers, or concrete piles depending on the foundation stabilization situation. Foundation underpinning methods should be determined by a professional engineer at a reputable foundation company.
Foundation Piering or Piles
There’s a big debate going on about round shaft piers versus square shaft piers. We believe each type of pier has a place depending upon the foundation underpinning situation. For compression applications JES utilizes round shaft piers and for tension applications square shaft piers are used.
Round Shaft Piers
Round shaft helical or resistance piers are designed for compression applications. Round shaft piers have a higher moment of inertia (resistance to bending) which makes them ideal for compression applications. The round shaft piers also have a higher installation torque rating and a higher lateral resistance because there’s a larger surface area exposed to the soil.
Square Shaft piers
Work best in tension applications, like wall anchors, soil nails or tie backs. However when installed under a building (in compression applications) the square shaft has warped and bent under the pressure. This is due to the socket and pin coupling which increases variances from straightness and can increase the potential of buckling. Shaft-to-shaft coupling is very difficult to achieve within the upset couplings of the square shaft since the load is then transferred through double sheer of the single coupling bolt.
The concrete piles are either pre-cast then driven into the ground, or cast-in-place. For cast-in-place concrete pillars a cylindrical shell is driven into the ground then filled with concrete.
There are considerations to take into account when using concrete piles: the force of driving can cause cracks and other problems in the surrounding structures, heavy machinery is required for installation which can create logistical challenges, and cast-in-place concrete pillars need time to harden and dry.
In certain applications concrete piles can be appropriate however the installation and side effects can be detrimental to surrounding structures. Because of these potential problems, we only use helical and resistance piers.
A square shaft is used for helical wall anchors which are installed in tension applications. The anchors are designed to provide lateral stability for foundation walls. Helical wall anchors can be installed in limited access areas without the use of heavy machinery, and installation doesn’t generate spoils.
Also called slab-jacking, is one of the methods used to stabilize a building’s foundation. Holes are drilled into the slab or under the foundation, and then concrete is pumped under the foundation. The theory is that the concrete will eliminate settlement problems.
While this foundation underpinning method can stabilize a foundation and even lift the building to its original position, it’s flawed. Without extending the stabilization solution all the way to the bedrock, there’s a likelihood that the building will begin to settle and shift again. However, mudjacking in conjunction with piering can offer a long-term solution to settlement and other foundation problems.
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At JES Foundation Repair our team of in-house foundation experts have warranted solutions for structural issues related to basement wall failure and settling foundations of all types.
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