Single Span - 35M Bridge on Spread Footing

[X-Wing]

I am about to re-design the foundation of a single span bridge, 35m long, on PSCG Type V. The hard part is that the natural ground in one abutment was already excavated. The shaft is about 5m high, the footing will be about 8.5x5m design for the excavated abutment. This is on the deepest side of the bridge (abutment b). meanwhile in abutment A, the size may be still reduced since the natural ground haven't yet excavated. The soil on the abutment A is practically already hard (about 400kpa).

Question: Is it generally advisable to have a single span bridge om different size of footing? Any insights on this? Thanks!

Very Truly Yours,

- andru18

 

[oldestguy]

You need to say more. Is this over a flowing stream? Any chance for scour? As to differing footing sizes, as long as the settlement is controlled, who cares what is buried?

 

[X-Wing]

thanks for the reply oldestguy,the abutment is over a flowing stream, about scouring, a little chance, maybe a little because the riverbed is mostly weathered rock, the banks are practically silty clay with some underlaying sandstones, but can easily be protected by bank protection.

Very Truly Yours,

- andru18

 

[oldestguy]

The scour subject is very important since the life of a bridge can be centuries, depending, and erosion protection can be destroyed by ice and debris in time. Thus, deep footing grade and possible deeper foundations (piles, caissons) might be better. This deserves review by an experienced geotechnical engineer.