Differential displacement is when one portion of a structure moves at a different rate relative to another portion of that structure. Differential displacement most often results from sub-surface mechanisms and can result in both cosmetic and structural damage. While sinkholes are most often suspected as the cause of differential displacement here in Florida; highly expansive clays, buried organic materials, erosion, and initial settlement can also contribute to differential displacement.

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If the structural integrity of a building has been or has the potential to be compromised, structural underpins may be required. Underpins are hydraulically driven or helically advanced pipe piles that get attached to the foundation with brackets. Based on the sub-surface mechanism affecting the structure, structural engineer will need to select the most appropriate approach to address the structure. Three such approaches exist.

A “Restorative” approach to underpinning is used to lift and/or re-level damaged and displaced portions of a structure. A “Stabilative” approach to underpinning is used to maintain a structure in its current state and prevent additional movement from occurring. And lastly, a “Preventative” approach to underpinning is used to isolate the structure from problematic soils which have the potential to cause future damage to the structure. It is important to note that while underpinning can be used to address structural displacement and damage, underpinning is not always required, and over-pinning can cause more damage to the structure than there was prior to pinning.

If you would like information on structural underpinning, our Structures Group is ready to assist you. Please contact Tim Roda at troda@brackenengineering.com.