When the Bell Bottom Pier method of foundation repair is selected the property owner has made a choice to employ the old fashioned method. Unlike other foundation repair methods, the Bell Bottom Pier method has been thoroughly tested and is the most reliable and most permanent solution for concrete slab foundations.
Prior to the actual drilling and belling process there has been an inspection of the building structure and its foundation. An experienced contractor will review the diagrams and suggestions for the placement of the piers. Usually Bell Bottom Piers can be placed every eight feet around the foundation perimeter and provide more than enough support for the foundation. If any internal support is needed then piers will be placed in interior locations.
A box must be dug at the pier placement site for several reasons. This box will be dug under and slightly outside the foundation perimeter. It will be approximately three feet by four feet with a depth of three feet. It will taper downward to a point where the pier shaft will be drilled. The purpose of the box is two fold. It will create space for the work crew to install the entire pier and the lower portion of the box will be the form for the concrete cap of the pier.
Once the box has been completed and all of the soil has been removed from the area, the work crew can begin the drilling process. The drilling process will remove soil for the shaft and the bell bottom or foot of the pier. The shaft will be drilled using a nine inch drill bit and therefore will have a final diameter of nine inches. The length of the shaft will depend on the soil test and location of stable soil or bedrock. Generally the shaft will be about eight to eleven feet long. The total length of the Bell Bottom Pier will generally be twelve to fifteen feet.
The work crew will begin drilling the Bell Bottom Pier shaft with a motorized drill. Each shaft and bell are dug with a two man team until they reach stable soil or bedrock. The drill or digging auger is placed on a vertical metal shaft that will be lowered as more soil is removed. The two man team must hold a T shape bar in a steady position while the metal shaft and drill are turning. The turning force is provided by a gasoline powered motor that compresses air. As a certain amount of soil is cut away the two man team will stop the turning of the drill and shaft. They will raise the drilling equipment and the cut soil from the hole. The soil will be placed in a wheelbarrow to be removed from the site. The two man team will repeat this process until they have reached the desired depth for the pier shaft.
During the drilling process one or more of the work crew will be assembling the steel rebar for the piers. The pier shaft will have three rods of steel placed inside the wet concrete. The cap of the pier will have two “mats” of steel rebar placed inside the wet concrete. The steel rebar will give the pier greater strength and longevity.
The final part of excavating soil for the pier is the belling process. A unique belling tool is attached to the vertical metal shaft and lowered down into the pier shaft. This tool has two flanges that will “fly outward” to cut the soil. These flanges will “fly outward” due to the centrifugal force of the spinning bell tool. The two man team will then raise the tool along with the soil that has been cut away. The cut soil will be inside the belling tool and the work crew will have to carefully remove the soil before continuing. They will repeat this process until the foot or bell bottom has been fully cut and excavated. The final foot will have a diameter of 22 inches and will rest on either bedrock or in stable soil.
The Bell Bottom Pier is now fully excavated. It consists of a cap, shaft, and bell bottom. It is now ready for the pouring of the wet concrete and placement of the steel rebar. It will provide a significant amount of support for the foundation that will rest on top.
Author Resource:
Martin Dawson is the co-founder (1984) of Dawson Foundation Repair. He is a leading authority in Texas and other southern states on repairing failed commercial and home foundations using the thoroughly researched drilled Bell Bottom Pier method. http://www.DawsonFoundationRepair.com/
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