Safe distance between 12" san swr line and pile driving operation

[ChipperB]

The bents for a flyover will be supported by 6-18" square concrete piles driven 62 feet in clay soil.

Is there a method to determine the safe distance between the pile driving operation and a 12" underground sanitary sewer line that is about 12 feet deep.

 

[PEinc]

Locate the sewer by test holes. Then drive the piles if they are about 3 feet clear. If not, locate the sewer and then drill in 6 casing pipes, 30 inch diameter, to just below the bottom of the sewer pipe. Clean out the casing pipes and then drive the 18" piles inside the casings. If the soil has sufficient cohesion, you may be able to drill without the casing pipes and drive the piles into the open holes.

If the sewer is clay pipe, I would drill. If steel, I would be a little bit less concerned but probably still drill unless I were about 5 feet away.