What Is Bearing Capacity?

Bearing capacity is a determination of how much weight soils can take, an important part of preparing to build on new ground. The soil's tolerance for loads can determine the overall limitations on any structure built on it, as well as the most appropriate choice of foundation. Geotechnical engineers can provide evaluations and advice on soil conditions. This might be required for some kinds of construction, and in others it is strongly recommended. An architect or contractor might order soil testing to determine the bearing capacity of a site.

If the load on the soil is too high, it can be subject to shear failure. Soil might move or settle under the building, which would threaten its structural integrity. This can be a particular concern in earthquake-prone regions, where buildings established on poor soil might collapse. Some soils also are subject to liquefaction, a phenomenon that can occur in earthquakes and in which the soil bubbles up from the earth as it weakens and loses cohesion.

Some soils have a very high bearing capacity. They can be suitable for shallow foundations, where the weight of a building transfers to the immediately adjacent soil. Such foundations tend to be less expensive to build and require fewer materials. For construction teams and architects, this style might be preferred, when possible, because using a shallow foundation cuts down on overall building time.

Such foundations are not suitable for weak soils. In situations where the bearing capacity is low, load-bearing pillars and supports must extend deep into the earth. They might anchor onto bedrock for the best support or can simply distribute the weight deeper, to an area of soil more capable of handling it. In some cases, the costs associated with a deep foundation might be so high that they limit the ability to build on a site, because the payoff of the construction might not be worth the effort needed to create a strong foundation.

Bearing capacity test results typically are kept on file along with the rest of the documentation for a project. In cases where government officials conduct their own soil testing for safety reasons or in preparation for a public works project, these results might be available to members of the public. Interested parties can request copies from government agencies and might be able to meet with a representative to discuss the meaning of the results. In other cases, the agency will provide the documentation, but citizens will need to hire their own consultants if they have trouble understanding the bearing capacity of a given site.