Strongback : The vertical members of a trench shoring system placed in contact with the earth, usually held in place against sections of sheeting with shores and positioned so that individual members do not contact each other
NFPA 1670 Standard on Operations and Training for Technical Search and Rescue Incidents, 2009 ed. https://www.nfpa.org/assets/files/AboutTheCodes/16 70/Errata1670-09-1.pdf, (Std: Opr and Trng for Tech Search and Rsq Incid - Amer) {408 NFC}