A shallow foundation is a type of foundation which transfers building loads to the earth very near the surface, rather than to a subsurface layer or a range of depths as does a deep foundation. A foundation is a Structure that transfers loads to the earth A deep foundation is a type of foundation distinguished from Shallow foundations by the depth they are embedded into the ground Shallow foundations include spread footing foundations, mat-slab foundations, and slab-on-grade foundations
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Spread footing foundation
Spread footing foundations consists of strips or pads of concrete (or other materials) which transfer the loads from walls and columns to the soil or bedrock. Embedment of spread footings is controlled by several factors, including development of lateral capacity, penetration of soft near-surface layers, and penetration through near-surface layers likely to change volume due to frost heave or shrink-swell.
These foundations are common in residential construction that includes a basement, and in many commercial structures.
Mat-slab foundations
Mat-slab foundations are used to distribute heavy column and wall loads across the entire building area, to lower the contact pressure compared to conventional spread footings. Mat-slab foundations can be constructed near the ground surface, or at the bottom of basements. In high-rise buildings, mat-slab foundations can be several meters thick, with extensive reinforcing to ensure relatively uniform load transfer.
Slab-on-grade foundation
Slab-on-grade foundations are a structural engineering practice whereby the concrete slab that is to serve as the foundation for the structure is formed from a mold set into the ground. Structural engineering is a field of Engineering dealing with the analysis and design of Structures that support or resist loads Structural engineering is Concrete is a construction material composed of Cement (commonly Portland cement) as well as other cementitious materials such as Fly ash and Slag The concrete is then placed into the mold, leaving no space between the ground and the structure. This type of construction is most often seen in warmer climates, where ground freezing and thawing is less of a concern and where there is no need for heat ducting underneath the floor.
The advantages of the slab technique are that it is relatively cheap and sturdy, and is considered less vulnerable to termite infestation because there are no hollow spaces or wood channels leading from the ground to the structure (assuming wood siding, etc. The termites are a group of Social Insects usually classified at the taxonomic rank of order Isoptera (but see also taxonomy Wood is hard fibrous lignified structural tissue produced as secondary Xylem in the stems of Woody plants notably trees but also shrubs , is not carried all the way to the ground on the outer walls).
The disadvantages are the lack of access from below for utility lines, the potential for large heat losses where ground temperatures fall significantly below the interior temperature, and a very low elevation that may expose the building to flood damage in even moderate rains. A flood is an overflow of an expanse of water that submerges land a deluge Remodeling or extending such a structure may also be more difficult. Over the long term, ground settling (or subsidence) may be a problem, as a slab foundation cannot be readily jacked up to compensate; proper soil compaction prior to pour can minimize this. In Geology, Engineering, and Surveying, subsidence is the motion of a surface (usually the Earth's surface as it shifts downward relative to The slab can be decoupled from ground temperatures by insulation, with the concrete poured directly over insulation (for example, Styrofoam panels), or heating provisions (such as hydronic heating) can be built into the slab (an expensive installation, with associated running expenses). Styrofoam is a trademark for polystyrene Thermal insulation, a material manufactured by Dow Chemical Company. Hydronics is the name for the use of Water as the heat-transfer medium in heating and cooling systems Some of the oldest and most common examples
Slab-on-grade foundations are commonly used in areas with expansive clay soil, particularly in California and Texas. While elevated structural slabs actually perform better on expansive clays, it is generally accepted by the engineering community that slab-on-grade foundations offer the greatest cost-to-performance ratio for tract and semi-custom homes. Tract housing (also known as cookie-cutter housing) is a style of housing development in which multiple identical or nearly-identical homes are built to create a community Elevated structural slabs are generally only found on large custom homes or homes with basements.
Care must be taken with the provision of services through the slab. Copper piping, commonly used to carry natural gas and water, reacts with concrete over a long period, slowly degrading until the pipe fails. Copper (ˈkɒpɚ is a Chemical element with the symbol Cu (cuprum and Atomic number 29 Natural gas is a Gaseous Fossil fuel consisting primarily of Methane but including significant quantities of Ethane, Propane, Water is a common Chemical substance that is essential for the survival of all known forms of Life. Copper pipes must be lagged, run through a conduit, or plumbed into the building above the slab. Plumbing, from the Latin plumbum for Lead, is the skilled trade of working with pipes, tubing and Plumbing fixtures for Electrical conduits through the slab need to be water-tight, as they extend below ground level and can potentially expose the wiring to groundwater. Groundwater is Water located beneath the Ground surface in Soil pore spaces and in the Fractures of lithologic formations
See also
- Building construction
- Construction engineering
- Fiber reinforced concrete
- Precast concrete
- Prestressed concrete
- Structural engineering
- Tie rod
- Rebar
- Steel fixer
- Formwork
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