Type Of Bridge Foundation | Bridge Engineering | Civil Engineering

Figure 1: Type Of Bridge Foundation

Bridge Foundation: Bridge foundation is the base of a bridge that transmits the load from the substructure (Abutments, piers, retaining walls, etc.) to the soil strata without any failure or not affected by scouring.

Depending on the nature and depth, the bridge foundation can be classified into the following types:

Types of bridge foundation | Bridge Foundation Type | Type Of Foundation Most Suitable For Bridges:

1. Open or Shallow foundation
2. Deep foundation.

Open foundation | Shallow foundation: This is the type of bridge foundation. A shallow foundation is suitable for moderate height structure, dry ground and hard soil strata or stone, etc where the complete structure settlement will be within acceptable limits and the supporting soil strata is available within 1.5 to 3 m below the bed Level of the watercourse and when the scouring is minimum. This is more economical than a deep foundation. This type of foundation can be classified into-

 A. Spread foundation: This type of bridge foundation is more suitable for moderate height structure, dry ground and hard soil strata or stone, etc where the complete structure settlement will be within acceptable limits and the supporting soil strata is available within 1.5 to 3 m below the bed Level.

 B. Raft foundation: This type of bridge foundation is suitable for the bridge where soft clay and silt and the hard soil is not available within reasonable depth (1.5 to 2.5 m) below the river bed. It is best suited in situations where the allowable bearing capacity of the soil is low and where is a possibility of unequal settlement due to heavy load.

 C. Grillage foundation: This type of bridge foundation is used to transmit heavy loads from substructure to the soils where the bearing capacity is low. This is used to avoids deep excavations and provides the necessary area at the base to reduce the intensity of pressure to the supporting area. This type of foundation is made up of rolled steel joists (grillage beams) provided in single or double tires and placed at a concrete pad.

Deep foundation: This type of bridge foundation is used when the existing soil is not stable enough to support the load and needs to transfer the loads further down the earth to utilize stable soil or hard strata. Deep foundations are generally more expensive than shallow foundations and the construction process of a deep foundation is more complex. But a deep foundation is essential for safety and maintaining the integrity of a structure. This type of foundation can be classified into-

A. Pile foundation: This type of bridge foundation is suitable where the support from the soil strata is not sufficient, constructional or economic conditions make it necessary to transmit loads of structures to strata that are beyond the reach of shallow foundations. Not only for supporting the structure, but piles are also used to help resist uplift, overturning, and lateral forces. . Pile foundations are constructed through driving performed and boring method. In the case of the driving method, the units are driven into the required founding level or hard strata. Drilling in and then driving tubes filled with concrete. The tubes shall be filled with concrete in different ways – they can be filled during or before withdrawal, or through drilling unlined, partly lined, or wholly lined boreholes before being filled with concrete.

B. Well foundation: This type of bridge foundation is suitable where good soil is available at about 3 m to 4 m below the bed level of the river and the bed consists of sandy soil. It is best suited to soft soils or sandy beds, where heavy scouring is Liable to occur due to excessive velocity of approach of the river water.

Picture:  Single Well

Picture: Twin Well

C. Caisson foundation: This type of bridge foundation is more suitable where hard strata are available near the river bed but the depth of water is excessive and it is not economically possible to exclude water from a dry bed for sinking the wells to provide a well foundation. This type of hollow substructure can be constructed near or on the ground surface and which is sunk to the desired level as a single unit. They have huge load-carrying capacity and are commonly used for bridge foundations.

          

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