Foundation Repair Case Studies: Foundation Settlement at Hospital

Thursday, October 26th, 2017

Challenge

Thrasher installed resistance piers to raise this hospital’s settling foundation.

Thrasher filled voids and brought the floor back to level.

Thrasher was hired to restore a foundation that had settled on three sides of the building over time. Indications of the settlement included severe cracks in the interior walls and floors and exterior masonry. This type of settlement caused doors and windows to malfunction or stick, drywall to crack and floors to become uneven. 

All buildings not constructed on a deep foundation system settle somewhat in the years following construction. This is to be expected but generally causes no problems if the settling is uniform across the building's foundation. But when one section of the foundation settles at a faster rate than the others, it can lead to significant structural damage to the building itself. Differential settlement can be caused by many factors, including weak soils incapable of supporting the structure's weight, poorly compacted soils, change in moisture conditions within the soil, etc.

Resistance piers can be used to stabilize and/or lift foundations that have settled or moved. They are one of the most commonly used types of piers in the Kansas City metro area due to the type of soil and structures in the area.

The solution to eliminating foundation settlement is to build the structure on a deep or intermediate foundation. Helical piers are a very common deep foundation, utilized industry-wide to prevent differential settlement. Helical piers are a factory-manufactured steel foundation system using hollow round shaft steel with helix plates attached. This system acts as a drill bit being screwed into the soil and advanced to a predetermined depth or installation torque. The installation torque achieved is a direct correlation to the capacity the pier will support. Standard sizes of helical piers range from 3, 3.5, 4.5 inches and larger diameter hollow round shafts. When debris, rock or other factors are present that don't allow a deep foundation system to be advanced deep into the earth, design and engineer teams will commonly turn to micro piles. Micropiles are a deep foundation capable of penetrating obstructions to bear the pile into competent bedrock or soil bearing strata. They are installed using drilling equipment capable of hammer drilling through rock, debris, or firm soils. The hollow steel shafts are equipped with a sacrificial drill bit ranging in size from 3-8inches in diameter. The pile is advanced by continuous hammer drilling and adding hollow bar extensions to achieve the designed depth. Once the drill bit and hollow bar sections have been drilled to the desired depth, the pier is then filled with high strength grout, which ultimately generates the skin friction required. These piering systems provide compressive capacities of up to 200 tons typically.   

Rest assured, though, when differential settlement does occur, no matter the reason, there is a fix. In this instance, the structure was not constructed on a deep foundation system, and differential settlement arose. Like all foundation settlement cases, Thrasher was able to work with client and engineering teams to design a system that would fix the settlement for good. Working with internal and external structural and geotechnical engineers, a design of 54 resistance piers was utilized to support the structure.      

Thrasher installed the 54 resistance piers/push piers at an average depth of 59-1/2 feet. Once the piers were installed, the structure was lifted back to level, and the piers were locked off to hold the structure in its current state and not allowing it to settle anymore. It was known during the design phase of this project that once the structure was lifted, there would be a need to lift, level, and void fill any concrete slabs in the vicinity of the area that had previously settled. Voids under the interior slab floor were filled, and the floor was then leveled utilizing mudjacking. Thrasher has since switched our methods of lifting and leveling concrete slabs from mudjacking to polyurethane foam or poly level. PolyLevel has proven to be a more user-friendly and reliable fix to concrete slabs that have settled. PolyLevel can be used in many applications, including sidewalk/driveway slabs, heavy highway slabs, grain silo slabs, railroad track ties, etc. If it has settled, we can lift and stabilize it.  

This project presented our crews with some challenging situations on the way to completing this project. Among them were:

Removing 55 cubic yards of concrete on one side of the building before installation could begin.

Avoiding seven 4" electrical conduit lines during excavation/installation.

Working around large pieces of mechanical equipment that surrounded the interior columns.

Additionally, Thrasher created a new design plan for the columns by adding to the existing footings in order to attain the strength necessary to lift the columns. This included rebar epoxy doweling and additional concrete added to the column footings to add depth, width and ultimately more strength. 

There are multiple options Thrasher has to offer to protect from or fix settlement issues. Our experienced design and install teams will do what it takes to provide you the most cost-effective and reliable system for your project.