How heave occurs | How can I deal with heave? | Back to heave
Under normal circumstances the soil moisture content surrounding the house is much the same due to similar weather conditions. If however, at the time of construction there was a tree already growing nearby, then this assumption is invalid because the clay will have been dried by the action of roots in the vicinity of the tree. Part of the house will be based on the dryer clay and part on the not so dry clay. If later, that tree is cut down or falls down or whatever, then the water demand that had existed pre-construction, is no longer present.
The result is that the ground in the course of time reverts back to the moisture content that it had prior to the tree growing. It thus becomes more equal to the moisture content remote from the tree. The effect is that the clay is enabled to increase its moisture content; this result in an expansion of the clay. The expansion cannot work downwards or sideways so it has to go upwards. As it goes upwards, it lifts your house up and there is nothing that you can do to stop the clay doing this, except that you have to isolate the house from the expanding clay.
The solution in this instance is to underpin down to a depth at which such expansion is not taking place and also to debond the connection between the expanding clay and the new foundations, so that the effects of such expansion do not unduly affect the new arrangement. Heave can also be caused by a leaking drain. The leak would normally be expected to be in one area giving rise to a local expansion, but it can be along a line. If along a line, say parallel to a flank wall, then the whole of the flank wall may be affected by some uplift.