The main causes of foundation failure

The purpose of foundations is to provide the necessary support for structures, providing resistance to the loads that act on them. Foundations function as structural systems, transferring loads to the soil under them, offering stability and resistance to the loads. Foundations are crucial to the structural integrity of any building, but in some cases are subject to failures. This article will explore the possible causes of foundation failure.

Types of foundation failure

Before looking at some of the causes of foundation failure, it is wise to get a grasp of the main types of failure, which are threefold:

  1. General Sheer Failure
  • Well defined failure pattern
  • Well defined failure load
  • Adjacent soil bulging
  • Sudden and catastrophic in nature
  • Tilting of the foundation is seen
  • Generally happens in stiff clay or dense sands at shallow depths
  1. Punching Sheer Failure
  • Pattern tricky to observe and not well defined
  • Failure load not well defined
  • No bulging of adjacent soil
  • Not catastrophic
  • No tilting
  • Generally happens in soft clays or loose sands at any depth
  1. Local Sheer Failure
  • Nnly clearly defined just below the foundation
  • Failure load is not well defined
  • Observable soil bulging on sides of the footing
  • No catastrophic collapse
  • Tilting of foundation may or may not be present
  • Somewhat in-between the other two categories in terms of characteristics
  • Usually occurs at any depth in medium stiff clay and medium-density sands

Main causes of foundation failure

Uneven soil settlement and uneven loading

A common cause of foundation failure, where cracks develop in the building and foundation reinforcements can corrode. This is usually caused by uneven load distribution or a change in soil-bearing capacity. The uneven loading of the structure can lead to uneven stresses, which cause differential settlement at areas where columns and walls transfer loads to the foundation.

Sub-soil moisture movement

This is an extremely common cause of foundation failure, taking place in cohesive soil predominantly. This can happen in areas where the groundwater fluctuates more frequently. The rise and fall of water tables can lead to intermittent soil compression and subsoil swell, leading to differing pressures and unless the foundation benefits from superb resistance against such pressures, it can fail.

Soil properties and insufficient compaction

Distinct areas of the foundation can rest on distinct soil types. If the build was based on one soil type, but part of the foundation rests on another, the foundation can fail due to differential movement. This is why a ground investigation is so crucial and must be thorough. In terms of insufficient compaction, this can yield air voids, where water and soil can become displaced leading to swelling, contraction and pressure on the foundations, which can result in failure.

Other major causes of foundation failure include:

  • Transpiration (from trees nearby)
  • Vibration from construction in the area