Explain geological consideration in Site investigation of Bridges.

Geological Consideration in the Site investigation of Bridges:

Bridge is defined as a structure built over a river to provide the line between opposite sides.some considerations are:

Lithology:

•  Nature of Bed Rocks:

1. The foundation Bedrock should be massive, hard, consolidated, stable and durable enough to bear different loads throughout the proposed life of the bridge.

2. Weaker rocks are unfavourable and special consideration should be taken.

• Depth of bedrock below River water:

1. Competent and hard bedrock should be available at shallow depth as far as possible.

2. Special measures should be taken if competent bedrock is not available even upto large depths.

Geological Structures:

1. Folding and faulting may cause some uncertainty in establishing a perfect geological profile but are not, othe....Show More

Geological Consideration in the Site investigation of Bridges:

Bridge is defined as a structure built over a river to provide the line between opposite sides.some considerations are:

Lithology:

•  Nature of Bed Rocks:

1. The foundation Bedrock should be massive, hard, consolidated, stable and durable enough to bear different loads throughout the proposed life of the bridge.

2. Weaker rocks are unfavourable and special consideration should be taken.

• Depth of bedrock below River water:

1. Competent and hard bedrock should be available at shallow depth as far as possible.

2. Special measures should be taken if competent bedrock is not available even upto large depths.

Geological Structures:

1. Folding and faulting may cause some uncertainty in establishing a perfect geological profile but are not, otherwise a negative factor.Acute fracturing and abundant jointing is, however, undesirable at the foundation level as these might cause settlement beyond the allowable limits.

2. When the bridge site are located in the zone of seismic activity, the foundations are required to be designed for additional seismic loads as specified in the codes of the respective areas. Factor of a scour cannot be ignored. 

Some additional factor that should be considered as follows:

1. The site should be at the minimum bank scouring of river due to water velocity.

2. Narrow width of river is favourable.

3. Less jointed and less fractured rocks are favourable.

4. Beds should be competent.

5. Fracture in filling should not be clay type.

6. Bedding should be across the river flow.

7. Site should be avoided from geological structures like faults, folds.

8. Water drainage should be studied. Special attention should be given to origin discharge of water catchment area of river. It is also studied for high level flood,debris potentiality etc.