Expert: Dan Griffin - 6/21/2008

Question
Hey Dan   
My situation is I need to put in a 36" culvert in a ditch that is always running between 12" and 30"s  of water. The soil is a soft loam , so I'm thinking to dig it out 18"Dx10'Wx250'L so I can get a cement truck on the back side of the property. And how do I dig out the 250' of driveway when theres water running into the newly installed culvert, do I need to go right up next to the culvert and dig from it , or dig from the other end and work towards the pipe? And when would I put the engineered rock in the dug out driveway bed?

Answer
Kim, see if you can divert or dam the water long enough to get the culvert installed.  If you have a swampy loam type soil you will probably need to improve the subgrade under the culvert, before you begin.  I think you might be terribly undersized with your choice of pipe, try to work with your county extension as many will help size and design.  They may also stop your work if you do not meet minimum sizing.  I assume this drive and culvert are at the public right of way.  Many people start out with too short a culvert and then constantly fight washing out both ends of the pipe.  It would be best to use concrete or major riprap at the head walls.  Spring run off can rip out and destroy culverts that are undersized or poorly bedded.  Once you have the culvert established and flowing, it really doesn't matter which end you work from.  I would think you would need a minimum of 2 feet of well compacted embedment over the culvert to stand dump and concrete trucks.

This drive is sounding ambitious.  If you remove the quantities you indicate, you are taking out about 150 cubic yards of existing soil and bringing in 185 tons of rock or whatever.  You are on the right track as it is always better to go deep the first time, as so many people spread a little gravel on top and keep rutting/sinking/and adding until they finally achieve a road bed.  I just want you to be aware of the quantities involved.  It would be best to lay down geotextile to help stabilize the bed, especially in low or boggy areas.  Crowning the road bed and providing drainage with barrow ditches should certainly be part of your original design.

I went to find an example of a head wall and came across this site which might be of interest to you:
www.tn.fifield.wi.gov/county/app/docs/fifield/200611081410344741121.doc;sesessionid=9Rlo1ORFCgNQtA8EPL9GJt3b  

This site did have some good pictures of headwalls:
www.epa.gov/owow/nps/unpavedroads/ch3.pdf