drainage detail at sheet pile wall
drainage detail at sheet pile wall
(OP)
We are working on a permanent sheet pile wall with precast concrete facing. Does anyone have a good detail for collecting the subsurface drainage behind the wall. I am thinking about drilling 2" weep holes every 8' thru the sheet pile and collecting the water in a 6" or 8" drain in front of the sheet piling. I have 2 concerns: drilling the hole in the sheet pile web (diagonal) and cutting a trench 5' in front of the sheet pile. Anybody have any experience with this?





RE: drainage detail at sheet pile wall
How high is the finished wall? How much ground water is there? Is there any special reason you are using steel sheet piling? Many walls are built with driven or drilled-in soldier beams, lagging, and pre-cast or cast-in-place concrete facings. Frequently, a wall needs to be tiedback if the soldier beams or steel sheeting can not cantilever. This would probably be the case if you add the extra 5 feet of excavation.
I would not worry too much about cutting weep holes through the sheet piling if they are near the neutral axis of the sheet piling. I would be more concerned with making a proper connection at the sheet pile wall so that water can properly get into the drain pipe without clogging or loss of soil into the stone backfill behind the precast panels. You may want to use slotted pvc pipe installed through the cut weep holes or perforated PVC pipe wrapped with a geotextile. These pipes could then be extended to the outlet drain pipe.
RE: drainage detail at sheet pile wall
The wall was designed by others and our firm is providing construction inspection and technical assistance. The sheet pile wall is in place - generally 15' high. The bottom (exposed) 18" of sheet piling is constantly wet with water pooling in front. Of course this is the rainy season and it will probably dry up in the summer.
The weep holes will be located 6" below the front grade elevation and empty into a pocket filled with 1/2" stone. We were going to put heavy filter fabric in front of the hole and rely on the rock fill to hold it in place. We will have perforated laterals at 9' centers running from the rock pocket to the 6" pipe running parallel to the wall.
The slope of an imaginary line from the ground elevation at the base of the sheet pile to the invert of the 6" drain will be about 20 degrees from the horiz.
RE: drainage detail at sheet pile wall
Sorry I misunderstood you about the 5 feet. But, like I said, some highway departments require the wall to be designed for an extra 5 feet just in case a future utility needs to be installed.