When determining the proper foundation for your structure, multiple site-specific factors must be evaluated in the planning stage. First and foremost, when determining which foundation type to be used, it is essential to understand the soil of the ground below the proposed design. This is accomplished by a Geotechnical Engineer that will provide recommendations based on the soil investigation as well as applicable seismic parameters for the area. Once the ground is evaluated, foundation types can be divided into two groups: shallow and deep. Understanding the type of structure and the loads to be applied to the foundation are equally imperative when designing the foundation.
Shallow Foundations are typically lightly loaded and for relatively low structures. They are just as they sound in that they are usually several feet deep – at most – and designed to frost depth to prevent frost heave, where applicable.
Deep Foundations are usually used with more heavily loaded and taller structures. These structures are more affected by both wind and seismic forces than lower lying and lightly loaded structures. This requires the applied loads to be transferred directly to the soils beneath the foundation. Deep foundations are also used where shallow layers of soil are weak and need to be penetrated for the applied loading.
Each type of foundation has its advantages and disadvantages that need to be analyzed when choosing a final design. These range from the required loading from the structure, soil conditions and the loading capability of the soil, as well as the cost to construct and maintain. A Professional Engineer should always be consulted in the foundation design and modification of all structure types to keep the structure sound and safe to occupy.