Caltrans Glossary
slaking/softening
"Slaking is the deterioration and breakdown of intact rock upon exposure by excavation and manifests as slabbing of material from the crown and sidewalls. Softening, which is dependent on wetting and exposure by excavation, is the reduction of intact rock strength at the invert or elsewhere and manifests as the development of a muddy or unstable invert or sloughing along segments of the tunnel perimeter elsewhere."

Definition from the "Caldecott Improvement Project: Geotechnical Baseline Report," prepared by Jacobs Associates, June 2009. 100 pp.

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