Lewis & Short

suffossĭo (subf-), ōnis, f. [suffodio], a digging under, undermining, Vulg. Jer. 51, 58.
Transf., in plur., concr., mines, Vitr. 1, 5, 5 (dub.): cum ipsum solum subfossionibus tremeret, Sen. Ep. 49, 8.