How important are the characteristics of the soil on your lot to the success of your foundation?

Improperly Designed Foundations

Before actual construction commences, builders/developers typically hire geotechnical engineering firms to analyze the characteristics of the soil in a particular area or subdivision. The geotechnical engineer analyzes the characteristics and sufficiency of the soil in a subdivision or area, and usually writes a report, including foundation design parameters based upon their study. This data is then usually utilized by a foundation design engineer to design the foundation. If the geotechnical data, or interpretation of that data, is inaccurate, the foundation may be improperly designed, and may have significant problems later as a result.

Soil Boring

Ideally, a soil boring of sufficient depth should be taken on each lot, since the characteristics of soil can vary in some situations significantly from lot to lot. However, many builders or developers do not take a soil boring on each lot, since the soil boring process, and analysis of each boring, can be expensive. Instead, borings may be spaced across the subdivision or area, sometimes as much as every 7-8 lots. The geotechnical engineer then develops an educated “guess” as to the characteristics of soil on those lots where no boring was taken based on the results of testing regarding the closest borings. Sometimes, this procedure is ill-advised, since the educated guess regarding the characteristics of soil in relation to those lots for which no boring was taken can be inaccurate.

Under-Designed Foundations

For example, in areas that transition from predominately clay to mostly limestone, the spacing of soil borings and the “educated guess” design process discussed may result in some instances in under-designed foundations. If you are having foundation problems, ask your builder or developer for a copy of your foundation design plan, and the geotechnical report for the subdivision or area. Determine if a soil boring was actually taken on your lot – if not, in certain situations the geotechnical data used in relation to the design of your foundation may be inaccurate, and may be a cause of the significant problems that you are having.