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The upward movement of the ground. This can be a result of several conditions. For the purpose of residential soil stabilisation, typical causes would be:

  • Clay - When a highly active, plastic clay absorbs enough moisture the clay can expand and possibly lift or heave structures or concrete situated above.
  • Grout - When injecting grout into the soil, a hydraulic action may be experienced which would cause the surface soil to rise. This type of Heave is often used in an effort to re-level structures that have settled and is often known as compensation grouting. When grouting around an existing structure, it should always be monitored with a survey instrument to detect heave.

High air entry filters - HAE

HAE (high air entry) is a term used for piezometer filters and often causes confusion as HAE actually means 'high RESISTANCE to air entry'.

HAE filters are normally ceramic with a 1 micron pore size and are used in low permeability media. Since the surface tension of the water in the very fine pores of the filter prevents entry of air, it is important that they are saturated before installation. All Geosense HAE piezometers are shipped pre-saturated with a special sheath to prevent them drying out.

Hooke's law

Within the elastic limit of a solid material, the deformation (strain) produced by a force (stress) of any kind is proportional to the force. For example, if a stress on a metal bar of 10 N/cm2 causes it to be compressed by 4mm, then a stress of 20N/cm2 will cause the bar to be compressed by 8mm.

If the elastic limit is not exceeded, the material returns to its original shape and size after the force is removed, otherwise it remains deformed or stretched. The force at which the material exceeds its elastic limit is called limit of proportionality.


An instrument error that causes a difference in the readings of an instrument when the indicated values are increasing compared with the readings at the same point when the values are decreasing. Instruments with a significant amount of hysteresis are not suitable for dynamic monitoring.