What is a Bell Bottom Pier? A Bell Bottom Pier is a vertical support structure designed to support concrete slab foundations. It is built by pouring wet concrete into an excavated hole and then placing steel rebar in the wet concrete. Its name is derived from the bottom of the pier, which resembles a bell. For home foundation repair the “bell” or foot provides a large 22 inch diameter area of support for the pier. Bell Bottom Piers will provide support and stability for a concrete slab foundations by resisting the forces of soil movement.
History of the Bell Bottom Pier
The Bell Bottom Pier was “invented” by an engineer named Willard E. Simpson in the early 1900s. Mr. Simpson was a graduate of MIT and he lived and worked most of his life in the central and gulf coast areas of Texas. He had received recognition for a number of his innovative solutions and designs for engineering challenges. One of his more interesting engineering solutions was to move the five-story, marble-clad Alamo National Bank Building in San Antonio. The bank was in the middle of a proposed street widening and the goal was to move the building several yards out of the path of the street widening while allowing the bank to remain operational during the entire moving process. Mr. Simpson used 1800 simultaneously-controlled screw jacks to raise the building onto rollers and then slide the building onto its new foundation. The success of this project, along with others, helped Simpson establish his reputation as a creative structural engineering consultant.
Drilled Piers for Highway and Bridge Construction (2012)
In the early 1900s architects and builders were designing and building larger and more complex buildings in Texas. However, Simpson realized he had a major problem when one of his buildings suffered severe damage due to soil movement. At that time there was no body of knowledge concerning expansive soils and geotechnical engineering. Mr. Simpson, therefore, embarked on an effort to study and analyze all foundation soils and footing types in San Antonio. In 1916 Mr. Simpson observed a local well driller, Ed Duderstadt, drilling 18 inch diameter holes in the soil with a mule walking in a circle and turning an auger. He realized he may have discovered a solution and he enlisted Mr. Duderstadt to help him drill similar holes for an experimental foundation. These drilled holes bypassed the unstable upper soils and continued down to the stable soils or bedrock. Simpson then filled these holes with concrete and steel rebar to create a new design for a foundation system. Thus, the “drilled pier” foundation system was born.
Mr. Simpson further refined his concept by reaming out the bottoms of these drilled shafts. He was prompted to do this because he needed a larger weight bearing area because buildings were becoming larger and heavier. The first of these reamed bottoms were done by lowering a man down the shaft who would carve out the under-ream (bell bottom) by hand. This was a slow and difficult process and a few years later Mr. Simpson and Mr. Duderstadt developed a mechanical device that would under-ream pier shaft bottoms. The Bell Bottom Pier was now fully developed and it has been used for 100 years to support buildings, bridges, and highway overpasses.
The Bell Bottom Pier has also become the “gold standard” for home foundation repair in Texas. Texas leads the nation in home foundation repairs because a majority of the home foundations built in Texas have been under designed and under engineered. Simply, the majority of concrete slab foundations that have been built, and that are currently being built, are not designed to be strong enough to withstand nature’s forces of soil movement. You can read more about this on our Why Foundations Fail page.
You can read more about the history of Bell Bottom Piers in the June 2006 issue of STRUCTURE magazine.
There are many Significant Advantages that Bell Bottom Piers enjoy over other Methods of Foundation Repair and you can read about them in the preceding link.
click here to see an Illustration of a Bell Bottom Pier used in foundation repair.
click here to read about the Quality Control for Bell Bottom Piers