Trench Shields – Part 6: Four Key Points

by David V. Dow on January 12, 2015

4 Key Points To Remember About Trench Shields

Key Point #1 — Trench shields must be installed in excavations in such a way to prevent lateral (side-to-side) or hazardous movement. In some instances, it may be necessary to back fill around a shield to fill large voids between outside of the trench shield and the trench walls.

There was too much space between the outside of the trench shield and the walls of the excavation, so the contractor back-filled around the shield. Note also that the top of the shield is even with grade, not below it. Further, there is a means of access and egress for the workers, allowing them to remain in the protected area as they enter and exit the trench work area.

 

Key Point #2 — It is OK to slope above the shield, provided you meet the following requirements:

  • The shield is rated for the full depth of the excavation, and
  • The slope starts at least 18″ below the top of shield, and
  • The angle of slope is based upon the manufacturer’s tabulated data and OSHA standards.

Key Point #3 — It is also OK to excavate up to 2 feet below the inside of the shield, provided that:

  • The shield is rated for the full depth of the excavation, and
  • There aren’t any indications of possible collapse of soil from behind or below the bottom edge of the shield.

Key Point #4 — Workers are never allowed inside a trench shield when it is being installed, removed, or moved vertically.

Always Remember…

The best shoring and shielding systems are useless if workers stray outside them. Workers must remain INSIDE the protected area at all times!

Coming up . . .

In the coming weeks we will take a look at Slide Rail Systems and Site-Specific Engineered Solutions.

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Trench Shield Components Can Be Dangerous

Because of the size and weight of trench shields, the processes of unloading, assembling, disassembling, and loading them can be dangerous. It is imperative that:

  • No person is ever underneath an overhead load.
  • Everyone watches for pinch points that are created with spreaders, sidewalls, etc.
  • A properly rated and inspected sling or chain (approved for overhead lifting) is used for handling.
  • Tag lines are used to control the shield.
  • Everyone watches overhead utilities and objects.
  • The crane or excavator that’s doing the lifting is rated to properly handle the load. As a rule-of-thumb, the crane or excavator must be rated to handle 1½ times (150%) of the weight of the trench shield, at the desired radius.
When handling trench shield components, everyone involved must work carefully, and use the proper rigging. When handling trench shield components, everyone involved must work carefully, and use the proper rigging.

Coming up . . .

In the coming weeks we will review 4 Key Points to remember when working with trench shields.

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Trench Shields – Part 4: Using & Handling Trench Shields

October 17, 2014

Using a Steel Trench Shield There are a several techniques for using steel trench shields. In stable soil, there are two steps: Excavate in front of the shield. Place excavator bucket around front spreader or use a chain/sling with pulling lugs, being careful not to damage the spreader or the collar. Pull the shield forward. [...]

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