IRSST - Institut de recherche Robert-Sauvé en santé et en sécurité du travail

Field Test of the JNIOSH Mini Strain Pipe Meter as a Safety Alert System during Trench-Work


Excavation work in trenches exposes workers to many risks. Collapses of the walls frequently cause workplace accidents on construction jobsites and must be avoided at all costs.

It is recommended that banks be excavated at a safe angle based on the soil type or that temporary retaining walls be used to stabilize banks (slopes). Nevertheless, it can be difficult to predict a collapse of the walls solely by visual observation. Monitoring sensors can be used to record small movements in the bank that would indicate an increased risk of collapse and warn workers of the situation. This would enable them to be evacuated from the site in time to avoid severe, even fatal, accidents.

Researchers at Japan’s National Institute of Occupational Safety and Health (JNIOSH) have developed and lab-tested a Mini Pipe Strain Meter (MPSM) adapted to Japan’s soils. This monitoring sensor measures the increase in shear stress in a bank’s shallow subsoil. This indicator signals an imminent wall collapse by issuing an audible signal.
The purpose of this study is to use the MPSM in situ in the vertical wall of a trench during field tests done in sensitive clay soil typical of Quebec, in order to study the sensor’s ability to correctly predict a collapse.

The ultimate aim is to help preventionists choose appropriate methods to protect against trench collapses, bearing in mind soil type and conditions and the water table.