Emergency Trench Shoring and Rescue: A Simplified Method for Calculating Lateral Earth Pressures

Abstract

Emergency trench shoring design for rescue operations has no reliable standard to determine lateral earth pressures. As a result, the first responder community is forced either to rely predominantly on either “rule-of-thumb” methods or similarly to assume the OSHA 29 CFR for Type C soil to determine a “worst-case scenario.” However, the use of generalized methods, i.e., the C-80, is not officially supported by OSHA standards, which are overly conservative and do not reflect the observations of actual trench surface failures. Additionally, the shoring system requirements can be unnecessarily prohibitive in short-term emergency operations. The current “rule-of-thumb” method used by first responders underestimates braced earth pressures for weak sandy soils and is not recommended for continued use. Therefore, a simplified soil mechanics-based lateral earth pressure framework, the “T-L method,” that accurately represents actual earth pressures based on the in situ soil failure conditions, is presented. The T-L method is validated against Coulomb earth pressure theories and braced excavation thrust pressures for Type C soils. The results indicate a significant reduction in estimated lateral earth pressures which are typically required for a standard construction shoring system design, while providing an adequate and safe emergency rescue shoring standard for first responders.