Cordyline Aspire Limited
Consulting Civil & Structural Engineers
 
   Home      Common Foundation Defects

Your text start HERE...

 
 
 
Common Foundation Defects 
 
 
Ground Movement

Ground movement is a natural phenomenon and results from changes in soil strength or volume resulting from changes in ground water level, moisture variations, 

 
 
Clay Shrinkage

Clay soils are particularly prone to variations in moisture variations.  These can result from prolonged dry weather, prolonged wet weather, and loss of moisture resulting from water demand of large trees or a reduction in the water demand following the removal of trees or hedges.  The strength of clay is dependent on its moisture content.  At shallow depth there is a considerable variation in moisture content throughout the year.  At greater depths this variation becomes very much smaller such that significant variation will occur only after prolonged drought of several dry years or a succession of very wet years.  The variation in strength is accompanied by a variation in volume with moist clay occupying a larger volume than dry clay.

In the UK the most pronounced effect is in the South East where the dominant soils type is London Clay.  The effect diminishes steadily with increasing distance from London.

As clays dry they lose strength and volume and can completely lose contact with the foundation.  A strong foundation could span over this void so formed but weaker foundations will sink and crack.

 
 
Clay Heave

Heave is the reverse of the above process.  If the water demand is diminished, for example by the removal of a large tree, the clay will absorb more water causing it to swell.  The top surface of the clay rises up with sufficient force to push foundations up also.  Once again the foundation loses contact with the ground over part of its surface and cracks form. The effect of heave can also be to push foundations outwards from the beneath the building.

 
 
Running Water

Running water can be from a natural source such as an underground stream or spring, or it can be the result of a broken drain.  The effect is to wash out fine particles or granular material from below the foundation giving rise to loss of volume, a change in the soil matrix and loss of strength.