Topic – Excavation Safety
Learning Outcomes – Participants will be able to: identify types of excavation collapses; identify the types of safe shoring/excavation techniques for working in trench excavations; describe the basic procedures for installing wood shoring in a trench excavation; describe how to work safety in a trench cage; determine the type of wood shoring needed for a trench excavation using the Manitoba shoring tables.
Time Steps Activity Materials
 

Introduction

Excavation Safety

  

120 min

Explain the Importance

Working in trench excavations is hazardous due to soil collapse, restricted access into some trenches, potential for flooding, utility contacts, unstable trees and existing building foundations due to excavating near them. To protect workers in excavations it is necessary for these workers to understand how to work safely in an excavation by installing wood shoring, working inside a trench cage or in a properly sloped excavation.

  
 

Show Learners

  • Review handout.
  • Before the Digging Starts – contractor must get an excavation permit from the Workplace Safety & Health Division and the utilities – Manitoba Hydro for electrical and gas clearances, MTS for telephones and fibre-optic cables as well as other communications companies, pipeline companies and cable companies. See the “Call Before You Dig – Manitoba” wed site
  • Types of Soil Collapse – use the handout and draw the types of collapse on the board/white board
  • Protecting Workers – emphasize that wood shoring must be installed according to engineer’s certification if trenches exceed depths outlined in the trench shoring tables. A properly sloped excavation wall is at a 1 to 1 slope or 45 degree angle.
  • Wood Shoring Components – explain that most shoring made of wood consists of upright and cross braces called “struts”. The use of walers – the long horizontal members supporting several uprights is not used very often due to the size and weight and the time needed to install. Upper left drawing: D = strut spacing; A = upright spacing; C = wale spacing. Lower Right drawing: A = upright spacing; B = strut spacing. Note: if plywood is used as sheathing to support bank behind the uprights, the struts/jacks must still bear on uprights. Ask participants why? Answer – if only bearing on plywood, struts/jacks could punch through sheathing.

Hand out – “Excavation Safety” Construction Industry Safety Regulations MR 189/85 – sections 107 to 139(3).