Shoring is one of the excavation safety procedure used to protect the edges of an excavation to prevent cave-in or collapse of the excavation.
Generally, shoring could be used to provide lateral support:
- To walls undergoing repair or reinforcement.
- During excavations.
- To prevent walls bulging out.
- When an adjacent structure is to be pulled down.
- When openings in a wall are made or enlarged.
Some materials which can be use for shoring includes: Timber, structural steel, and framed tubular scaffolding.
Before we get back to shoring excavation, let us consider the different shoring technique:
This involve the use of rakers, typically placed at 3-4.5 m centres, and braced at regular intervals. They tend to be inclined at between 40-75º.
Dead Shoring or Vertical shoring:
These are primarily used to carry vertical loads from walls, roofs and floors. This is often required when an opening is being made in a wall, or a defective load bearing wall is being rebuilt. An arrangement of beams and posts support the structural weight and transfer it to the firm ground foundation.
Flying shoring or Horizontal shoring:
Flying shores are used as an alternative to raking shores and provide a clear working space at ground level by exerting thrust on opposite walls, often the party walls of two buildings. Often this is used in combination with raking shore principles.
Going back to our main point of concern “Shoring excavation”, from the different shoring techniques explained above, it is very obvious that the flying/horizontal shoring technique is what suits the excavation.
How to do Shoring for Excavation
This imply making use of one or more of the shoring techniques to safeguard an excavation.
Note: Shoring is used when the location or depth of the cut makes sloping back to the maximum allowable slope impractical.
Shoring systems consist of posts, wales, struts, and sheeting. Lets move on to consider the types of shoring available at our disposal.
Types of shoring for excavation
There are two basic types of shoring for excavation:
- Timber shoring and
- Aluminum hydraulic shoring
As the name implies, timber showing makes use of timber to protect collapse of excavation.
The hydraulic shores are prefabricated strut and/or wale system manufactured of aluminum or steel. Hydraulic shoring provides a critical safety advantage over timber shoring because workers do not have to enter the trench to install or remove hydraulic shoring.
Other advantages of most hydraulic systems are that they:
- Are light enough to be installed by one worker;
- Are gauge-regulated to ensure even distribution of pressure along the trench line;
- Can have their trench faces “preloaded” to use the soil’s natural cohesion to prevent movement; and
- Can be adapted easily to various trench depths and widths.
Hydraulic shoring should be checked at least once per shift for leaking hoses and/or cylinders, broken connections, cracked nipples, bent bases, and any other damaged or defective parts.
To do shoring for excavation, you have to first determine the type of shore you want to use – Timber shoring or Hydraulic shoring. After determining the type of shoring you want to use, make the materials available, then get a trained personnel to fix it up for you.
You can equally learn how it is done.
NOTE: There must be routine inspection plan for any shoring type adopted. This will help prevent failure of the structure.
In conclusion, excavation accidents that are most common occur due to “cave ins” and excavation walls collapsing. OSHA reports that excavation accidents usually result in injury and death.
Shoring is one of the most effective excavation safety technique which could prevent these accidents; as this provision of a support system for trenches helps prevent movement of soil, underground utilities, roadways, and foundations.