Foundation Failure: Causes, Types, and What to Do

Why Foundations Matter

Foundations provide the necessary support for structures, transferring loads to the soil beneath them and offering stability and resistance. They are crucial to the structural integrity of any building, but can be subject to failures that manifest as cracks, movement, and instability above ground.

Types of Foundation Failure

There are three main types of foundation failure:

• General shear failure — typically occurs in stiff clay or dense sands at shallow depths. Characterised by sudden tilting of the foundation, adjacent soil bulging, and a well-defined failure pattern. This is catastrophic in nature.
• Punching shear failure — occurs in soft clays or loose sands at any depth. No tilting, no catastrophic collapse, and the failure pattern is difficult to observe.
• Local shear failure — falls between the other two categories. May occur at any depth in medium stiff clay or medium-density sands.

Main Causes of Foundation Failure

Uneven soil settlement and loading — a common cause where cracks develop and reinforcements corrode. Caused by uneven load distribution or changes in soil-bearing capacity.

Sub-soil moisture movement — extremely common in cohesive soils. Fluctuating water tables lead to intermittent soil compression and subsoil swell, creating differing pressures on foundations.

Soil properties and insufficient compaction — different areas of a foundation may rest on different soil types. If the original ground investigation was inadequate, differential movement can result. Insufficient compaction leaves air voids where water and soil can become displaced.

Other causes include vibration from nearby construction and transpiration from trees drawing moisture from the soil.

Need professional help with this?

Specific Structural Inspection (SSI) — fixed price from £480, including site visit and Building Control-ready documentation.