incompetent rock

incompetent rock

[in′käm·pəd·ənt ′räk]
(engineering)
Soft or fragmented rock in which an opening, such as a borehole or an underground working place, cannot be maintained unless artificially supported by casing, cementing, or timbering.
References in periodicals archive ?
The major cause of the slump and earth flow in the investigated area is because of water saturation in the regolith Gharbina meandering stream and the underlying incompetent rocks of the Kurram Formation/group.
4) A possible mechanism for deformation of the Gachsaran Formation is flow of salt and of other incompetent rocks (members 2-5).