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Posted: Fri Nov 24, 2006 2:56 am
by Ian-Mitch
Hi all - I'll try and keep it simple 
There's a storm ditch in the top RH corner of my garden, which turns 90 degrees from my neighbours house (ie my RH fence) to the back fence. My neighbour and I - working together - have put 600mm culverting in his garden, the end of which pokes out slightly into my part of the ditch.
Basically, I want to culvert this small section by adding 600mm pipe to the end of his pipe, turning it in my ditch in two 45 degree bends, and out of the back fence (to the rest of the ditch on common land). The area that the ditch cuts across is only about 15 foot square, so not much pipe is needed.
I already have a big length of 600mm diameter culvert - and am wondering whether to try and mitre the joints in a couple of places, covering with 300g DPM (to keep the soil out) and concrete them in for stability. OR I'm thinking it may be better to buy the specialist 45 degree bends - although they are £500 each and I'd need two.
I intend to cover the finished work with spoil and deck over it.
Any opinions on what's best? The flow in the ditch can be quite strong at times (recent storms have been gushing through my neighbours pipe half way up the pipe). Obviously, I dont want the job to collapse in a couple of months. How easy would it even be to mitre the pipe with a normal saw and get a reasonable joint?
As I'm posting this at 2.50 am you can see its keeping me awake - and as usual I want to crack on with the job this weekend.
Thanks for any advice, Ian
Posted: Fri Nov 24, 2006 8:03 pm
by lutonlagerlout
what is the culvert pipe made of?? concrete or plastic??
you should be able to mitre them with a stihl saw if you are careful and remember water will always take the easiest course.
are those bends really a monkey each??
i suppose as long as you dont mind a bit of seepage a mitre will be ok
cheers LLL
Posted: Fri Nov 24, 2006 9:52 pm
by Ian-Mitch
Thanks LLL -
They're made of plastic; I gave it a go today and the mitre joints turned out OK. So I'll pack them in with shingle tomorrow so it should work OK.
Managed to get a better price on the joints (from Polypipe) - still £375 each though. Ouch!
thanks for the advice, Ian
Posted: Sat Nov 25, 2006 8:43 am
by seanandruby
dont under estimate the power of water going full bore. are the joints tight? i suspect there are big gaps at one end where the water will force out anything it hits. it could force the pipes out eventually. you probably will need some sort of thrust block especially at the end of a run into a ditch. maybe sand bags filled with concrete to build wing walls and act as thrust blocks. you have to bear in mind the erosian with the velocity of the discharge. a header wall and slope may be needed. i dont know how to put a picture of a converson on here but if you know where there is a simular outlet go and have a look. the environment agency might help, or, not. good luck.
Posted: Sun Nov 26, 2006 2:34 am
by Ian-Mitch
Thanks sean, you're right the water has some force when it comes through. I hope I've done enough to hold the turn in place - let me briefly explain the job.
Curved around the exterior 90 degree corner of the existing ditch are about 50 (existing) cement bags - been there years so they seem to work. At the entrance to the corner my pipe is fitted snug with next door's pipe using the existing collar fitting. Each pipe is mitred (as best I could - there's gaps of course) and then lined up to the next - kinda going around the corner in three straight lines.
The pipes were lined up carefully and then packed in place with 5 tons of shingle. I put geo membrane between the joints to keep out the shingle is best i could and 300g DPM over the top to protect the top of the joint from the (4 foot) of earth that will go on top.
At the exit of the run is a concrete lintel over the pipe (to build a small retaining wall to keep the earth in which will eventually go over the pipe). Either side is a concrete shuttering (I think thats what its called) to help keep the last pipe in place and the shingle from washing away.
I guess what's now bothering me is whether the shingle will keep the three pieces lined up so the water keeps flowing through. Clearly water will be swilling around the pipe exterior as well. Any opinion/suggestions?
Sorry for the long post but I hope its more helpful to explain the job properly to get anyones POV .... thanks as ever, ian
Posted: Sun Nov 26, 2006 7:45 am
by Dave_L
Concrete would have been better as a pipe 'support' medium esp in a radius situation.
I'd be too concerned that the shingle would wash away.
Posted: Sun Nov 26, 2006 8:20 am
by seanandruby
i agree you need a solid block for the thrust. i usually bring the pipe in straight then concrete a sloping base adding reinforced mesh, have some mesh sticking up where the wing walls are going to be and cast some kickers in situ "thats a low upstand to kick the timber falsework shuttering against". cast about 200ml of the end of the pipe in the header wall. the base should splay out towards the stream, ditch etc. you can probably do the job with sand bags instead of shuttering because it is a lot of work and waste. you would be surprised that pipework can push up through shingle as the water gets higher they float. thats worst case scenario. you say you are building a wall on top of your work? how deep are the founds do they surround the pipe.? see what its like after the bad weather mate. hope i havent put you off? 
Posted: Sun Nov 26, 2006 11:55 am
by Ian-Mitch
Thanks both - well, its early days but water is hurtling through there at the moment and it seems to be holding well. I need to get some extra weight (soil) on the pipe to stop it floating (yikes) but the mini digger is getting close to the ditch and the muds all sloppy - so of course, safety first before I do anything.
Based on the advice I'm going to get as much concrete in as possible to support the thrust (so to speak ). The founds will be as deep as I need to be - but will go either side of the pipe. All told, I'm thinking of decking over the whole job using two concrete piers either side of the ditch - so worse case scenario is that the job will erode under the decking but as thats all held in place seperately it shouldnt matter too much.
Need a brew and a ham toastie to mull things over - ahh, the missus just offered one up. Happy days
thx, ian