Bridge Abutment Hydrostatic Pressure
Bridge Abutment Hydrostatic Pressure
(OP)
I have a bridge abutment that is retaining about 8 feet of soil. The bridge is over a small creek and I am providing weep holes at 4 ft on center in the wall. The area is very wooded and the project is going in to the DOT for approval before clearing the woods. After clearing, a geotech is going to go in and drill to determine the allowable pile capacities to support the abutment.
I am not sure what lateral pressure to design the abutment for. I was going to assume 60lb/ft3 for lateral earth pressure, but what about hydrostatic pressure? Are weep holes normally considered sufficient to eliminate water buildup behind the wall on a creek bank? There could be seepage of water from the site to behind the wall. I imagine most the runoff in the area is leading toward the creek, so I expect it to be moist at the banks. I don't know about the water table at the site.
I am not sure what lateral pressure to design the abutment for. I was going to assume 60lb/ft3 for lateral earth pressure, but what about hydrostatic pressure? Are weep holes normally considered sufficient to eliminate water buildup behind the wall on a creek bank? There could be seepage of water from the site to behind the wall. I imagine most the runoff in the area is leading toward the creek, so I expect it to be moist at the banks. I don't know about the water table at the site.





RE: Bridge Abutment Hydrostatic Pressure
As far as weeps - I would make sure you backfill with a clean granular material against the wall to facilitate drainage TO the weeps.
RE: Bridge Abutment Hydrostatic Pressure
I am just a little nervous using their dry lateral soil pressure in this wet wooded area, adjacent to a creek. It is a decent sized pedestrian bridge the abutment will be supporting.
My question really comes down to this; can you assume hydrostatic pressure is not an issue behind any wall as long as you provide adequate number of weep holes and proper granular fill? Couldn't the soil hold water but yet not be 100% "saturated" thus still affecting the lateral earth pressure?
RE: Bridge Abutment Hydrostatic Pressure
I guess that in this situation, I would not use a higher pressure, but go the extra mile in ensuring that the water gets out. That might mean using more gravel, more weeps, or even a secondary system in addition to the weeps such as a perforated pipe with drain fabric that draws the water away from the structure.
We structural dudes love redundancy, right?
RE: Bridge Abutment Hydrostatic Pressure
RE: Bridge Abutment Hydrostatic Pressure
Regards,

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RE: Bridge Abutment Hydrostatic Pressure