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Foundation Movement - Explained

Slab on ground foundation with post tension cables


Regardless to the type of foundation, there are two common reasons for foundation movement:


1)    Response to soil volume change (shrink, swell or settle): Response to soils means that foundation will move in the direction the supporting soils move. The simplest way to understand this is to understand that soils move in four directions: up, down, and the sides (left and right).


2)    Response to loading (settlement of foundation due to load on soils): Foundations can also move in response to how much load (weight) the foundation is carrying. Movement caused by loading is typically associated with the foundation transmitting the load to the soils than the soils can support. The movement is similar to settlement, downward movement. Whether the movement is caused in response to the soils or loading, the key point to understand is that foundations are design to move to some degree.


Considering that foundations are designed to move, foundation “stabilization” is not feasible and should not be expected. There are distinct differences in definitions to foundation “stabilization” between the foundation repair industry and accepted engineering principles.


The foundation repair industry defines stabilization as limiting the movement of the foundation in the “downward” direction only. Downward movement is common for settling soils, however, foundations can also move upward (heaving soils) which sometimes gets misdiagnosed as foundation settlement. Recall that soils are expected to move in four directions: up, down and to the sides. That being said, foundation “stabilization” as defined by the foundation repair industry seeks to “stabilize” foundations in only one direction, down (commonly due to settlement or shrinking of soils).


Contrary to the foundation repair industry definition to foundation stabilization, the engineering industry defines “stabilization” of the foundation as a method of reinforcing or altering the soils to reduce the potential for the soils to move. The method of soil reinforcement or alteration depends on engineering judgement aimed at limiting the movement in some desired direction. That being said, care should be taken in expecting foundations not to move or to be “stable”