Installation and Removal of Shoring and shielding in Excavation safety Training

Shoring and shielding:

Shoring and shielding systems can prevent cave-ins in excavations with or without sloped / benched faces. The safest way to install and remove them is from outside the excavation.
The shoring (temporary support structure) must be designed to withstand allexternal forces that may be caused by:
  • soil pressures
  • water pressures
  • nearby structures
  • additional loadings and vibrations (heavy equipment, traffic, temporary piled materials near the excavation, etc.)
Shores are vertical or horizontal supports that prevent the faces of an excavation from collapsing. Vertical shores are called uprights. They’re easy to install, relatively inexpensive, and often used in stable soil or in shallow excavations that have parallel faces. Vertical shores must be sized for the excavation’s dimensions and soil type.
Horizontal shores are called walers. Walers are often used when unstable soil makes sloping or benching impractical and when sheeting is necessary to prevent soil from sliding into the excavation.
Shields provide employees a safe work area by protecting them from collapsing soil. Shields don’t prevent cave-ins but “shield” workers if a face does collapse. They are usually placed in the excavation by heavy equipment.

Installation of Shoring:

When installing shoring within a trench type excavation, appropriate procedures must be followed to provide for a safe excavation.
Uprights, struts (screw jacks), wales and plywood must be installed according to the shoring table that is based on the soil conditions, depth and width of the trench and excavation.
When installing shoring, the bucket of the excavation machine must be placed in the trench directly in front of the shoring being installed. The bucket will serve as additional protection if a cave-in occurs.
An appropriate ladder must be provided in a trench or open excavation. The ladder must extend at least one metre (three feet) above ground level at the surface of the excavation and be within three metres (10 feet) of a worker's working position inside the excavation.
Shoring struts/jacks must be installed from the top down. It is important that the top (first) strut/jack is placed approximately 0.5 metres (18 inches) below the surface, and the second strut/jack is placed according to the shoring table. Installing the first and second strut/jacks is necessary to support the vertical uprights that stabilize the excavation walls.
When plywood is used as sheathing material, the jacks must be placed on the uprights that support the plywood. Jacks or struts must never be installed directly on to the plywood. If the walls move, the jack or strut could push through the plywood.
Once the worker has at least two struts/jacks placed on each set of uprights, the worker can proceed to install the bottom strut/jack. There must never be less than two struts/jacks used on each set of shoring.
This procedure must be followed with each set of shoring. This method protects the worker with the bucket of the digging machine and the shoring already
Shoring and shielding systems are available from manufacturers in a variety of dimensions, usually aluminum or steel, or they can be custom-built from tabulated data approved by a registered professionalengineer. Manufacturers will also provide tabulated data with their systems that includes engineering specifications, depth ratings, special instructions, and system limitations.

Shoring Removal:

The procedure to remove shoring is the opposite of the procedure for installation. Struts are removed in the opposite order that they were installed. There must never be less than two sets of uprights in place. Workers removing the shoring must always stay between the shoring in place for protection.
Prior to removing a strut or jack, the trench should be back filled to a depth equal to the elevation of the strut or jack being removed. This back filling procedure shall be performed prior to removal of each strut or jack.
Sequence for the Installation and Removal of Shoring

SHIELDS ( trench boxes ):

Shields, otherwise known as trench boxes, are generally used in open areas, but also may be
used in combination with battering and benching.
The excavated area between the outside of the trench box and the face of the trench should be as small as possible. The space between the trench box and the excavation side must be backfilled to prevent lateral movement of the box. Shields MUST not be subjected to loads exceeding those which the system was designed to withstand.
Shields can be used in the four different trenching situations indicated below:
(1) The shield rests on the excavation bottom and extends above the surface.

(2) The trench is narrowed and the shield is supported. When this method is used the shield must be tightly wedged into the trench.

(3) The top of a shield in a slope battered trench shall  be a minimum of 0.5 metres above the ground level.

(4) When an undersized shield is used, thetop of the trench SHALL be stabilised by battering. The maximum height of the battering SHALL be a maximum of 1.0 metre.

  • Shields SHALL only be installed by a worker holding a current certificate of competency under the Lifts and Cranes Act.
  • Heavy equipment SHALL always be used to place the box or shield in the trench.If there is sloping toward the
  • excavation/trench, the trench box must extend at least 0.5 metres (18 inches) above the surrounding area. This can be done by providing a benched area adjacent to the box.
  • Any modifications to the shields must be approved by the manufacturer.
  • Workers SHALL only enter and leave the shield by using a ladder.
  • Trench boxes may ride 0.6 metres (2 feet) above the bottom of an excavation, provided they are calculated to support the full depth of the excavation and there is no caving under or behind the shield.
  • When shields are used as the only means of ensuring safety in the trench, workers SHALL NOT
          (1) enter the excavation/trench before the shield has been installed
          (2) work inside the trench, outside of the protection of the shield
          (3) enter the excavation/trench after the shield has been removed
  • Workers SHALL NOT remain in the shield while it is being moved.


  • The competent person SHALL check the work site and adjacent areas for the presence of aerial conductors.
  • If aerial conductors are present and there is a possibility that the workers or plant will come within 10 metres of the conductors, the owner of the power supply/ electrical apparatus must be contacted to determine the nominal voltage.
  • All conductors SHALL be considered to be alive and uninsulated.
  • A trained safety observer SHALL be present and observing the work being carried out when there is a situation that any part of the plant being used for theexcavation/trenching work or load being delivered to the work site COULD enter the exclusion zone. eg 3 metres.
  • The excavation equipment while the minimum clearances are maintained.
  • If the excavation equipment is to be operated within the ‘no-go’ exclusion zone, work SHALL NOT commence until (1) the owner of the power supply/electrical apparatus is informed in writing of the nature and duration of the intended work and (2) written permission is received from the owner of the power supply/ electrical apparatus. A copy of these documents SHALL be kept on file.
  • The workers must not allow any part of their body or any hand held tools within the ‘no-go’ exclusion zone.

Stability and adjacent structures:

Make sure that structures, roadways, and sidewalks adjacent to the excavation are adequately supported.
  • Use an appropriate support system – such as shoring or bracing – if the excavation could affect the stability of nearby buildings, sidewalks, and roads.
  • Don’t excavate below the base or footing of any foundation that might endanger employees unless you do one of the following:
  • Use a support system that protects employees and keeps the structure stable.
  • Ensure that the excavation is in stable rock.
  • Have a registered professional engineer determine that the structure will not be affected by the excavation work.
  • Have a registered professional engineer determine that the excavation work will not endanger employees.

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