Heave is defined as the resulting upward movement of an underlying soil layer due to the addition of moisture to an unsaturated expansive soil. When water is added to an expansive soil (such as clay), large volume changes occur. This results in an expansion of the soil in an upward direction. Soil heave is often seen as the opposite of subsidence or settlement, where the soil moves in a downwards direction.
Trenchlesspedia Explains Heave
Soil heave may be caused by one of the following:
- Stress relief due to removal of soil or other above-ground structure
- Change in water table elevation
- Leaking pipelines resulting in change in moisture content
- Freezing and subsequent expansion of water in soil
Soil heave is potentially destructive to structures such as building foundations and roadways. The damage resulting from construction operations, such as directionally drilled crossings, has become a concern for government municipalities and contractors due to the rise in popularity of trenchless construction techniques.
Some of the factors that affect the rate and severity of soil heave during trenchless construction include:
- Borehole pressures
- Rate of back-reaming
- Soil properties
- Soil moisture content
- Annular space size
- Downhole tooling
Engineers and contractors involved in trenchless construction must be cognizant of soil heave and necessary steps taken prevent its occurrence.