hi everybody, I have came across a

[h1pat]

hi everybody,
I have came across a situation where we are going to construct a box culvert over a small stream. To allow the construction of box culvert, a by pass pipe will be constructed running parallel to the proposed box culvert.
The box culvert is about 9'x22' in c/s and its invert is about 15feet below the existing grade. It also has a a cutoff wall and gravel pad which makes the total excavation of about 18' below the exisitng grade. The by pass pipe is about 2' away from the box culvert ( we cannot move the pipe away from the culvert since there exist 60"dia. sanitary sewer line about 8'from the by pass)with an invert level same as that of the bottom of stream ie. 8'. That means with in 2 ft of distance we will have a cut of apprx. (18-8')10 ft, which is critical. Therefore we are providing sheeting (sheet piles ) over there. The rock is shallow approx. 20' below the exisitng grade and its a sandstone with good RQD. As per thumb rule to provide cantilever sheeting for an excavtion of approx. 18 ft we need about 15 to 18 ft of embedment which, looking at the RQD is not possible. Even anchored pile is not possible since there is no room for a deadman. Toe pins could be a solution, but it comes out with high nos and more depth. We can not even brace the pile since we don't have enough room.

thanks for ur help in advance..

 

[Qshake]

In some cases, the rock is drilled (side by side holes) to form a rock cut that will accept the end of the sheet pile. After drilling the pile are seated into the cut. Of course, this would require bracing at intermediate levels as you come up the piling.

In this case you may need to brace the sheet from one wall to the other wall as you excavate toward one end of the culvert. I assume this is not a long culvert.

Just a thought.

 

[h1pat]

thanks for your prompt reply..
but how can we provide intermediate braces with in 2-ft of distance. there is only 2-ft gap between the box culvert and by pass pipe. ---SHEET PILE WALL WILL BE BETWEEN THE CULVERT AND BY-PASS PIPE....

 

[Qshake]

I misunderstood you and thought that some type of shoring protection would also be required for the other side of teh culvert as well. Assuming this were the case, internal bracing could be used. This internal bracing would then span the culvert plus any overexcavation.