Shallow foundation

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Shallow foundation construction example

A shallow foundation is a type of building foundation that transfers structural load to the earth very near to the surface, rather than to a subsurface layer or a range of depths, as does a deep foundation. Customarily, a shallow foundation is considered as such when the width of the entire foundation is greater than its depth. [1] In comparison to deep foundations, shallow foundations are less technical, thus making them more economical and the most widely used for relatively light structures.

Contents

Types of shallow foundation

Footings are always wider than the members that they support. Structural loads from a column or wall are usually greater than 1000kPa, while the soil's bearing capacity is commonly less than that (typically less than 400kPa). By possessing a larger bearing area, the foundation distributes the pressure to the soil, decreasing the bearing pressure to within allowable values. [2] A structure is not limited to one footing. Multiple types of footings may be used in a construction project.

Wall footing

Also called strip footing, this footing is a continuous strip that supports structural and non-structural load bearing walls. Found directly under the wall, Its width is commonly 2-3 times wider than the wall above it. [3]

Detail Section of a strip footing and its wall. In-ground-foundation.gif
Detail Section of a strip footing and its wall.

Isolated footing

Also called single-column footing, it is a square, rectangular, or circular slab that supports the structural members individually. Generally, each of its columns gets its footing to transmit and distribute the load of the structure towards the soil underneath. Sometimes, an isolated footing can be sloped or stepped at the base to spread greater loads. This type of footing is used when the structural load is relatively low, columns are widely spaced, and the soil's bearing capacity is adequate at a shallow depth.

Combined footing

When more than one column shares the same footing, these are called combined footing. Utilized when the spacing of the columns is too restricted, that if isolated footing were used, they would overlap one another. Also, when property lines make isolated footings eccentrically loaded, combined footings are preferred.

When the load among the columns is equal, the combined footing may be rectangular. Conversely, when the load among the columns is unequal, the combined footing should be trapezoidal.

Strap footing

A strap footing is when individual columns are connected to one another with the use of a strap beam. The general purpose of a strap footing is alike to those of a combined footing, where the spacing is possibly limited and/or the columns are adjacent to the property lines.

Mat foundation with its concrete undergoing curing. Raft-slab.jpg
Mat foundation with its concrete undergoing curing.

Mat foundation

Also called raft foundation, it is a single continuous slab that covers the entirety of the base of a building. Mat foundations support all the loads of the structure and transmit them to the ground evenly. Soil conditions may prevent other footings from being used. Since this type of foundation distributes the load coming from the building uniformly over a considerably large area, it is favored when individual footings are unfeasible due to the low bearing capacity of the soil.

Diagrams of the types of shallow foundations. Types of Shallow Foundations.svg
Diagrams of the types of shallow foundations.

Slab-on-grade foundation

Slab-on-grade or floating slab 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. 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. That being said, Frost Protected Shallow Foundations (or FPSF) which are used in areas of potential Frost Heave, are a form of Slab on Grade Foundations. [4]

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. The slab can be decoupled from ground temperatures by insulation, with the concrete poured directly over insulation (for example, extruded polystyrene foam panels), or heating provisions (such as hydronic heating) can be built into the slab.

Slab-on-grade foundations should not be used in areas with expansive clay soil. 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 homes. Elevated structural slabs are generally only found on custom homes or homes with basements.

Copper piping, commonly used to carry natural gas and water, reacts with concrete over a long period, slowly degrading until the pipe fails. This can lead to what is commonly referred to as slab leaks. These occur when pipes begin to leak from within the slab. Signs of a slab leak range from unexplained dampened carpet spots, to drops in water pressure and wet discoloration on exterior foundation walls. [5] Copper pipes must be lagged (that is, insulated ) or run through a conduit or plumbed into the building above the slab. Electrical conduits through the slab must be water-tight, as they extend below ground level and can potentially expose wiring to groundwater.

See also

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<span class="mw-page-title-main">Wall</span> Vertical structure, usually solid, that defines and sometimes protects an area

A wall is a structure and a surface that defines an area; carries a load; provides security, shelter, or soundproofing; or, is decorative. There are many kinds of walls, including:

<span class="mw-page-title-main">Earth shelter</span> House partially or entirely surrounded by earth

An earth shelter, also called an earth house, earth bermed house, or underground house, is a structure with earth (soil) against the walls, on the roof, or that is entirely buried underground.

<span class="mw-page-title-main">Floor</span> Walking surface of a room

A floor is the bottom surface of a room or vehicle. Floors vary from simple dirt in a cave to many layered surfaces made with modern technology. Floors may be stone, wood, bamboo, metal or any other material that can support the expected load.

<span class="mw-page-title-main">Retaining wall</span> Artificial wall used for supporting soil between two different elevations

Retaining walls are relatively rigid walls used for supporting soil laterally so that it can be retained at different levels on the two sides. Retaining walls are structures designed to restrain soil to a slope that it would not naturally keep to. They are used to bound soils between two different elevations often in areas of inconveniently steep terrain in areas where the landscape needs to be shaped severely and engineered for more specific purposes like hillside farming or roadway overpasses. A retaining wall that retains soil on the backside and water on the frontside is called a seawall or a bulkhead.

<span class="mw-page-title-main">Basement</span> Below-ground floor of a building

A basement or cellar is one or more floors of a building that are completely or partly below the ground floor. Especially in residential buildings, it often is used as a utility space for a building, where such items as the furnace, water heater, breaker panel or fuse box, car park, and air-conditioning system are located; so also are amenities such as the electrical system and cable television distribution point. In cities with high property prices, such as London, basements are often fitted out to a high standard and used as living space.

<span class="mw-page-title-main">Foundation (engineering)</span> Lowest and supporting layer of a structure

In engineering, a foundation is the element of a structure which connects it to the ground or more rarely, water, transferring loads from the structure to the ground. Foundations are generally considered either shallow or deep. Foundation engineering is the application of soil mechanics and rock mechanics in the design of foundation elements of structures.

<span class="mw-page-title-main">Seismic retrofit</span> Modification of existing structures to make them more resistant to seismic activity

Seismic retrofitting is the modification of existing structures to make them more resistant to seismic activity, ground motion, or soil failure due to earthquakes. With better understanding of seismic demand on structures and with recent experiences with large earthquakes near urban centers, the need of seismic retrofitting is well acknowledged. Prior to the introduction of modern seismic codes in the late 1960s for developed countries and late 1970s for many other parts of the world, many structures were designed without adequate detailing and reinforcement for seismic protection. In view of the imminent problem, various research work has been carried out. State-of-the-art technical guidelines for seismic assessment, retrofit and rehabilitation have been published around the world – such as the ASCE-SEI 41 and the New Zealand Society for Earthquake Engineering (NZSEE)'s guidelines. These codes must be regularly updated; the 1994 Northridge earthquake brought to light the brittleness of welded steel frames, for example.

This page is a list of construction topics.

In construction or renovation, underpinning is the process of strengthening the foundation of an existing building or other structure. Underpinning may be necessary for a variety of reasons:

<span class="mw-page-title-main">Natural building</span> Sustainable construction practice

Natural building is the construction of buildings using systems and materials that emphasize sustainability. This in turn implies durability and the use of minimally processed, plentiful or renewable resources, as well as those that, while recycled or salvaged, produce healthy living environments and maintain indoor air quality. Natural building tends to rely on human labor, more than technology. As Michael G. Smith observes, it depends on "local ecology, geology and climate; on the character of the particular building site, and on the needs and personalities of the builders and users."

<span class="mw-page-title-main">Concrete slab</span> Flat, horizontal concrete element of modern buildings

A concrete slab is a common structural element of modern buildings, consisting of a flat, horizontal surface made of cast concrete. Steel-reinforced slabs, typically between 100 and 500 mm thick, are most often used to construct floors and ceilings, while thinner mud slabs may be used for exterior paving (see below).

<span class="mw-page-title-main">Precast concrete</span> Construction material

Precast concrete is a construction product produced by casting concrete in a reusable mold or "form" which is then cured in a controlled environment, transported to the construction site and maneuvered into place; examples include precast beams, and wall panels for tilt up construction. In contrast, cast-in-place concrete is poured into site-specific forms and cured on site.

<span class="mw-page-title-main">Deep foundation</span> Type of foundation

A deep foundation is a type of foundation that transfers building loads to the earth farther down from the surface than a shallow foundation does to a subsurface layer or a range of depths. A pile or piling is a vertical structural element of a deep foundation, driven or drilled deep into the ground at the building site.

Basement waterproofing involves techniques and materials used to prevent water from penetrating the basement of a house or a building. Waterproofing a basement that is below ground level can require the application of sealant materials, the installation of drains and sump pumps, and more.

<span class="mw-page-title-main">Expanded clay aggregate</span> Lightweight aggregate made by heating clay at high temperature in a rotary kiln

Lightweight expanded clay aggregate (LECA) or expanded clay (exclay) is a lightweight aggregate made by heating clay to around 1,200 °C (2,190 °F) in a rotary kiln. The heating process causes gases trapped in the clay to expand, forming thousands of small bubbles and giving the material a porous structure. LECA has an approximately round or oblong shape due to circular movement in the kiln and is available in different sizes and densities. LECA is used to make lightweight concrete products and other uses.

<span class="mw-page-title-main">Rigid panel</span>

Rigid panel insulation, also referred to as continuous insulation, can be made from foam plastics such as polyurethane (PUR), polyisocyanurate (PIR), and polystyrene, or from fibrous materials such as fiberglass, rock and slag wool. Rigid panel continuous insulation is often used to provide a thermal break in the building envelope, thus reducing thermal bridging.

<span class="mw-page-title-main">Waffle slab foundation</span>

The Wafflemat foundation system, also called a waffle slab foundation, is an above-ground mat foundation used to provide load-bearing capacity on expansive, rocky, compressible, or hydro collapsible soils. The slab is created by placing a series of plastic forms ("Waffleboxes") that are either 8.5 or 12 inches in height, and 19 by 19 inches in plan, directly on grade to create a waffle-like grid of ribs, and then monolithically pour a post-tensioned reinforced concrete slab over the Waffleboxes. The completed slab then sits on the ground as a 'raft', with the void areas underneath the slab allowing for soil movement.

<span class="mw-page-title-main">Grade beam</span>

A grade beam or grade beam footing is a component of a building's foundation. It consists of a reinforced concrete beam that transmits the load from a bearing wall into spaced foundations such as pile caps or caissons. It is used in conditions where the surface soil’s load-bearing capacity is less than the anticipated design loads.

<span class="mw-page-title-main">Strap footing</span>

A strap footing is a component of a building's foundation. It is a type of combined footing, consisting of two or more column footings connected by a concrete beam. This type of beam is called a strap beam. It is used to help distribute the weight of either heavily or eccentrically loaded column footings to adjacent footings.

References

  1. Akhter, Shahin. "Shallow foundation – Definition, Types, Uses and Diagrams". Pro Civil Engineer. Retrieved July 31, 2021.
  2. Gillesania, Diego Inocencio T. (2004). Fundamentals of reinforced concrete design (2nd ed.). [Cebu, Cirty, Philippines]. p. 259. ISBN   971-8614-26-5. OCLC   1015901733.{{cite book}}: CS1 maint: location missing publisher (link)
  3. Mahdi, Sheikh. "8 Most Important Types of Foundation". civiltoday.com. Retrieved July 31, 2021.
  4. "Slab-on-Grade Foundation Detail & Insulation, Building Guide".
  5. "Slab Leak Repair McKinney, Frisco, and Allen Tx - Hackler Plumbing". Hacklerplumbingmckinney.com. 2013-11-08. Retrieved 2018-08-20.