ravelly ground

ravelly ground

[′rav·lē ′grau̇nd]
(geology)
Rock that breaks into small pieces when drilled and tends to cave or slough into the hole when the drill string is pulled, or binds the drill string by becoming wedged or locked between the drill rod and the borehole wall.
References in periodicals archive ?
Barrels of expanding two-part polyurethane grout were pumped above the TBM shield and in front of the cutterhead to solidify ravelly ground and fill the voids.