2 Methods Of Foundation Underpinning Used By Renovation Contractors

Posted on: 22 February 2017

Underpinning is a versatile technique used to renovate sinking, tilting, or cracked concrete foundations. While historically there was just one main form of underpinning, today there are numerous different ways the technique can be implemented, depending on the nature of the particular problem. If you would like to learn more about the types of underpinning systems used by remodeling contractors, read on. This article will discuss two of the ways this general technique can save a foundation.

Pit Underpinning

Pit underpinning is the oldest and most basic method of foundation underpinning. It is also the most labor intensive. Nonetheless, it remains a perfectly viable option, and one that makes it particularly well-suited for older buildings that were not originally constructed with a footed foundation. The shallower the foundation in question, the easier it is to employ pit underpinning.

The idea behind pit underpinning is relatively simple: the soil beneath the foundation is excavated and replaced with freshly poured concrete. Of course, in practice things aren't quite that simple, since you can't exactly dig out the entire foundation all at once. Instead, the installation must proceed step-wise, with a certain volume of soil being excavated and replaced with concrete before moving on to the next. At the end of the process, you are left with what amounts to a foundation beneath your foundation.

Beam And Base

Beam and base underpinning is a more modern variant of pit underpinning. The idea here is that the entire foundation does not need to be underlaid with fresh concrete, just a few strategic locations. These locations generally correspond to the existing foundation's feet--in other words, those places that are bearing the brunt of the foundation's weight.

Like pit underpinning, beam and base underpinning utilizes a concrete base to provide stability. However, here the concrete is reinforced with steel beams to provide the maximum amount of support for the foundation's feet. Both the size and the depth of the concrete base must be determined based on the existing ground conditions. This determination will take into account such factors as soil composition, moisture level, and depth of the water table. 

Likewise, it is necessary to determine the most appropriate beam design--in other words, how much steel reinforcement should be added to the concrete base. This aspect weighs factors such as the building's structural configuration and the amount and location of the applied loads. Should the soil beneath the foundation contain a high amount of clay, which has a tendency to expand greatly when exposed to water, so-called anti-heave design elements will also be added to the concrete base. Contact a business, such as Lehman Construction Services Inc, for more information about remodeling.