Listening and discussion

Text “Foundation (engineering)”

A foundation (also called a groundsill) is a structure that transfers loads to the earth. Foundations are generally broken into two categories: shallow foundations and deep foundations.

Shallow footings are, usually, embedded a meter or so into soil. One common type is the spread footing which consists of strips or pads of concrete (or other materials) which extend below the frost line and transfer the weight from walls and columns to the soil or bedrock. Another common type is the slab-on-grade footing where the weight of the building is transferred to the soil through a concrete slab placed at the surface

Deep footings

A deep footing is used to transfer a load from a structure through an upper weak layer of soil to a stronger deeper layer of soil. There are different types of deep footings including helical piles, impact driven piles, drilled shafts, caissons, piers, and earth stabilized columns. The naming conventions for different types of footings vary between different engineers. Historically, piles were wood, later steel, reinforced concrete, and pre-tensioned concrete.

Monopile footings

A monopile footing utilizes a single, generally large-diameter, footing structural element to support all the loads of a large above-surface structure.

A large number of monopile footings have been utilized in recent years for economically constructing fixed-bottom offshore wind farms in shallow-water subsea locations. For example, a single wind farm off the coast of England went online in 2008 with over 100 turbines, each mounted on a 4.7-meter-diameter monopile footing in ocean depths up to 18 meters of water. An earlier wind farm in the North Sea west of Denmark utilizes 80 large monopiles of 4 meter diameter sunk 25 meters deep into the seabed.

The base-isolating footing design is believed to be a powerful tool of contemporary earthquake engineering pertaining to the passive structural vibration control technologies.

Design

Footings are designed to have an adequate load capacity with limited settlement by a geotechnical engineer, and the footing itself is designed structurally by a structural engineer.

Other design considerations include scour and frost heave. Scour is when flowing water removes supporting soil from around a footing (like a pier supporting a bridge over a river). Frost heave occurs when water in the ground freezes to form ice lenses.

Changes in soil moisture can cause expansive clay to swell and shrink. This swelling can vary across the footing due to seasonal changes or the effects of vegetation removing moisture. The variation in swell can cause the soil to distort, cracking the structure over it. This is a particular problem for house footings in semi-arid climates such as South Australia, Southwestern US, Turkey, Israel, Iran and South Africa where wet winters are followed by hot dry summers. Raft slabs with inherent stiffness have been developed in Australia with capabilities to resist this movement.

When structures are built in areas of permafrost, special consideration must be given to the thermal effect the structure will have on the permafrost. Generally, the structure is designed in a way that tries to prevent the permafrost from melting.