Foundation (civil engineering)
A foundation is the lowest part of a structure that transfers all superstructure loads safely to the underlying soil or rock, ensuring stability against settlement, sliding, and overturning. Foundations are broadly classified as shallow foundations (spread footings, combined footings, raft/mat foundations) when the depth of embedment is small relative to width, and deep foundations (piles, caissons, well foundations) when loads must be transferred to deeper, stronger strata. The design of foundations requires knowledge of both the structural loads imposed from above and the geotechnical properties of the soil below, making it an interdisciplinary activity bridging structural and geotechnical engineering.
Comparison of Foundation Types and Their Suitability
| Foundation Type | Depth Range | Load Range | Suitable Soil | Common Use |
|---|---|---|---|---|
| Isolated footing | 0.5–2 m | Light to moderate | Firm soil, SBC > 100 kPa | Individual columns, houses |
| Combined footing | 0.5–2 m | Moderate | Firm soil, close columns | Adjacent columns, boundary |
| Strip footing | 0.5–2 m | Moderate | Firm to medium soil | Load-bearing walls |
| Raft / mat foundation | 0.5–3 m | Heavy, widely distributed | Weak or variable soil | Tall buildings, tanks |
| Pile foundation | 5–50 m | Very heavy | Soft clay, loose sand | Bridges, high-rise buildings |
| Well / Caisson foundation | 10–30 m | Very heavy, lateral loads | River beds | Bridge piers in rivers |
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Related Terms
Soil Mechanics
Soil mechanics is the branch of geotechnical engineering that applies the principles of mechanics and hydraulics to the engineering behaviour of soils, studying their strength, deformation, permeability, and consolidation under various loading conditions. Founded by Karl Terzaghi in the early 20th century, it provides the theoretical and experimental framework for analysing slope stability, bearing capacity, settlement, earth pressure on retaining walls, and seepage through embankments. In India, soil mechanics principles underpin all foundation design codes including IS 1904, IS 6403, and IS 8009.
Bearing Capacity (soil)
The bearing capacity of soil is the maximum load per unit area that a soil can support without undergoing shear failure, excessive settlement, or instability below a foundation. The ultimate bearing capacity (q_u) is the stress at which the soil fails in shear, while the safe bearing capacity (q_s) is q_u divided by a factor of safety, and the allowable bearing capacity also accounts for permissible settlement. Terzaghi's bearing capacity equation, later extended by Meyerhof, Hansen, and Vesic, expresses q_u as a function of soil cohesion, surcharge, foundation width, and soil friction angle, forming the basis of IS 6403 in India.
Structural Column
A structural column is a vertical compression member that transmits axial compressive loads from beams, slabs, and other upper-structure elements down to the foundation, and may also resist bending moments arising from lateral loads or eccentric loading. Columns are classified by their slenderness ratio (effective length divided by radius of gyration) into short columns, which fail by material crushing, and long (slender) columns, which fail by elastic or inelastic buckling before the material reaches its yield stress. In reinforced concrete design to IS 456, columns are also classified as axially loaded, uniaxially bent, or biaxially bent based on the combination of forces they carry.
From Old French "fondation" and Latin "fundatio" (a laying of the bottom), from "fundare" (to lay the bottom, found), from "fundus" (bottom, base). The term has been used in English since the 14th century in both the literal engineering sense and the figurative sense of a basis or starting point.