What is heave

All buildings are supported by the ground beneath them and all buildings will settle, or subside over the years as the ground adjusts to supporting the weight of the building.

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All buildings are supported by the ground beneath them and all buildings will settle, or subside over the years as the ground adjusts to supporting the weight of the building.

This happens with all types of ground conditions. Heave is the opposite of this and is the upward movement of the ground which supports foundations of a building.  Foundations moving upwards may sound an unusual situation but this can principally happen in two situations.

The most common place occurrence of heave is when there are clay ground conditions.  A good deal of London and the Home Counties have this sort of ground supporting our homes and properties so are susceptible to this.  

However, clay is not an entirely stable material due to how it changes its behaviour under different moisture conditions.  As clay is impermeable, if water is added or removed from one particular area such that the moisture content of the clay changes, then that effect will be very localised and an adjacent area of clay will not experience any of the same changes.

If the moisture levels in clay reduce due to perhaps a dry summer or an adjacent tree then the clay will shrink as it becomes dryer, withdrawing away from the foundations above.  As it withdraws, the foundation will follow it under the force of gravity, so the foundation will move downwards.  This is known as subsidence or settlement. The opposite will happen if moisture levels increase.  The clay will swell and apply an upwards force on the foundations and the foundations will move upwards in response.  This upward movement of the foundations is known as heave.  Heave can cause as many issues as subsidence since any movement of one area of the foundations more than another can cause cracking.

A less common form of heave is when large scale excavations are undertaken, such as creating a new basement.  A storey height of soil weighs a great deal and removing this burden from the soil beneath a basement will cause the remaining round to swell since it is not longer pressed down by the soil above.  That swelling, similar to the swelling as moisture levels increase, is known as heave.

As leading structural engineers with extensive experience in this field, Structures-Made-Easy can inspect your home or property and report on whether such issues have arisen and how best they might be addressed.

If you would like to discuss further please feel free to contact us using our email support@structures-made-easy.co.uk or call us on 0207 965 7376

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