Slide 1
A foundation transfers building forces into the ground
A foundation carries loads from a structure into the ground. It spreads or redirects those forces so the ground and structure can work together.
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The ground is not a uniform rigid block. Soil layers, groundwater and previous disturbance vary across a site, making investigation part of design rather than a detail postponed until excavation.
Slide 2
A larger footing can reduce average pressure
A spread footing distributes a load over a larger area. This can lower average contact pressure, though the actual distribution may be uneven.
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If the resultant load is off-centre, one side can experience greater pressure than the other. A footing’s size must therefore be considered together with moments and horizontal forces, not weight alone.
Slide 3
Uneven settlement can cause damage before ground failure
A foundation may avoid ground failure yet settle too much. Different settlement between supports can be especially damaging to a structure.
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Uniform downward movement and differential movement have different consequences. Floors, walls and service connections may tolerate one better than the other, so acceptable settlement depends on the supported system.
Slide 4
Piles use resistance along their sides and bases
Piles and shafts can transfer load through side resistance and resistance at their base. They connect the structure with suitable deeper ground.
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Their capacity does not come solely from reaching rock. Installation method, soil interaction and group behaviour influence performance, and neighbouring piles may not act as independent copies of one isolated pile.
Slide 5
Groundwater can change conditions after construction
Groundwater affects effective stress, the stress carried by the soil’s solid framework. It also affects construction conditions and some soil movements.
Drainage or erosion can change conditions after a foundation is built.
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Near waterways, scour can remove supporting material around a foundation. Long-term design therefore considers how the site may evolve, not only the soil profile measured on one investigation date.
Sources
- Shallow Foundations
Federal Highway Administration
- Structural Stability in Bridge Construction
Federal Highway Administration