In the construction of foundations for buildings, timbering is used to prevent the collapse of side soil into the trenches. Trenches are excavated open space to facilitate foundation work.
The main difference between timbering and shoring is that timbering is used for small excavation while shoring is used for larger depths.
Importance and Necessity of Timbering in Foundation Construction
- Timbering is necessary to prevent earth slides because of loose soil.
- Timbering is used for the safety of pedestrians and vehicles.
- To support the soil beneath surrounding properties timbering is used.
Methods of Timbering for Trenches
- Box Sheeting
This is used when the depth of timbering is not more than 4 meters. In Box Sheeting wales, struts, bracings, and sheeting are used to construct the temporary structure.
- Sheet Piling
They are used when subsoil water is present. Sheet piles are able to resist larger earth pressures.
- Vertical Sheeting
In this type polling boards are placed vertically to make sheeting. Vertical sheeting is used for deep trenches say more than 10 meters.
They are used for extremely loose and soft ground where timbering is necessary just after trenching.
- Stay Bracing
This type of timbering is used where depths are less than 2 meters.
Members Used in Timbering
Here is a brief explanation of the different members used in timbering is given.
- Sheeting: It is a process of combining polling boards. Sheeting could be done either vertically or horizontally.
- Polling Board: This is in the direct contact with the soil in trenches. Polling board is placed vertically to prevent soil entering in the pit.
- Wales / Walling: They are used to support the polling boards and are perpendicular to the polling board.
- Bracing: It is a diagonal member used between the walls.
- Strut: They are horizontally placed to support opposite polling boards.