Subsidence is the downward movement of the surface of land, which can be caused by a number of sources. Subsidence can have serious consequences to buildings, railway tracks or roads that are standing on the surface.
In terms of trenchless construction or rehabilitation, subsidence is often caused by the disturbance of the ground under the surface due to drilling activities.
Trenchlesspedia Explains Subsidence
Trenchless activities can disturb the stability of the ground around the drilling trajectory. It is important for geotechnical information of the site to be examined before deciding on a specific trenchless technique so that the risks of subsidence can be minimised. For example, when drilling through loose soil, it is advisable to use a technique like pipe jacking, so that the ground is supported by the casings as the drill progresses. In this way, there is no risk of a collapse in the drill path, which would cause subsidence at ground level.