How shall I level thee…let me count the ways.
Because each home and underlying soil condition can be different, there is no easy answer that applies to all concrete foundation repair situations. Each case needs to be examined individually by an independent structural engineer or professional foundation repair contractor. Some contractors will have biases to one method over another because they only perform one type of service.
Leveling or underpinning a concrete foundation is performed using piers. The piers are used to provide support for an area of the foundation that needs to be raised. The four main types of piers used in underpinning are drilled concrete piers, concrete pressed pilings, steel piers and helical piers. The type of soil under your home and the type of foundation determines which pier should be used. As always, use only as directed.
Here is a quick overview of the most common foundation repair techniques:
Resistance or push piers often have the best lifting potential for foundation repair. This is because these types of piers are “pushed” or “rammed” down into the ground, through the inadequate soil until they hit a hard surface or load bearing stratum. The weight of the structure is used as a counter-force to hydraulically push these piers into the ground. Once they hit this bottom, they can be pushed even further so that they actually lift the structure back to their original level. The advantage of this type of pier is that a soils report is not really necessary to know how deep the piers must be pushed. It becomes self-evident. Once the “bottom” is reached the structure can be lifted. These types of piers are typically used for heavier structures but are also perfect for single story residential homes. Like the one I live in.
Helical piers are most often used to support a concrete slab but not lift it. These types of piers are twisted into the ground much like a corkscrew. Each pier has one or more “flights” that are like blades that do the pulling into the ground. These flights keep the pier in place after installation. The advantage of a helical pier is that is can be used on very light structures like a porch. However, to install a helical pier properly, a soils test should be performed by a geotechnical engineer to determine how far down the soil is sturdy enough to support the structure. After all, if you turn a helical into loose soil, it loses most of its holding strength and who wants a flaccid pier?
Helical piers are very useful in other applications such as tie-backs. Since they are screwed into the ground, and held in place with their flights, not only can they support downward pressure, but then can support an equal amount of outward force. They can hold things like retaining walls into the ground. Helical piers can be used in pre-construction situations. They are installed before the foundation is placed to prevent any future foundation settlement. Also, helical piers can be used in conjunction with resistance piers on hillside homes to lift the structure and keep it in place. Except in parts of California.
Both resistance and helical piers are made in a variety of configurations to support a variety of structures. The selection of the proper pier is an important calculation the foundation repair contractor must make prior to quoting a job. Ya got yer steel pilings, and concrete pilings held together with steel cable or rebar. Pressed pilings can be held together with steel and concrete or just weight and friction. Weight and friction also describes one of my sister-in-laws.
The bell bottom pier method uses freshly poured concrete on-site that forms a bell shaped foot in load bearing soil and is reinforced with rebar. The depth, size and location of the shafts can be custom designed for your house. The bell bottoms are hidden pretty far underground so your neighbors can’t seem them and make fun of you.