Abstract
Labor accidents frequently occur in trench excavations so that workers are buried of collapsed soil. Main cause of the accidents was luck of an installation of retaining walls to support the trench walls. In addition, workers failed to escape because they were not aware of an increase of the risk prior to failure. This study discusses on availability of simplified monitoring for prevention of the labor accidents. A full scale model test was carried out in a model ground composed of soft deposit of Kanto-loam and Compact strain meters of developed sensors were installed to measure increment of shear strain θ in shallow subsurface near the trench shoulder. Trench wall did not fail immediately after a completion of the final excavation, and 23 minutes of time lag existed prior to failure. The relationship between θ and the displacement shows good agreement in the increase. Similar reactions to the creep strain curve were observed in θ. A couple of minute time could be provided for escape by identifying either 2nd or 3rd creep. A clear increase of θ was observed at the shoulder area when the trench became unstable. It was clarified that the potential threat of trench failure can be detectable by the monitoring.
