Vijay Posted August 19, 2017 Share Posted August 19, 2017 I'm struggling on a drain run and only have a fall of 1:28 (the fall is 540mm over 15m). I can cut the concrete of the foundation if I really have to but I wondered if there's any tips to lower the incline? The manhole that I'm connecting into has a 160mm inlet, can I use a 160 to 110mm level invert reducer and have it so the 110mm is at the top? That could buy be 50mm. The Floplast mini inlet chamber's side inlet is 100mm above the outlet. Am I allowed to use the side inlet to change direction if i don't have any flow into the main inlet (that flows straight through to the outlet). If I could, that could buy me 100mm. A mate suggested using a couple of say 15 degree elbows to give the pipe a kick down. I think the idea would work but don't know if it's allowed or be a potential blockage place. I also wonder how that would affect rodding. 1 Link to comment Share on other sites More sharing options...
Oz07 Posted August 19, 2017 Share Posted August 19, 2017 (edited) People say blockages occur if pipe too steep. However if you were to set 2 ic's up around 4' apart I reckon you could get away with a steep fall between. I can't remember finding a blockage in a too steep section of pipe. Much less a 4" smooth plastic pipe with decent velocity. Have a word with your BCO he might even be ok with IC and rodding eye. Otherwise you can do backdrop but above seems simpler to me Edited August 19, 2017 by Oz07 Link to comment Share on other sites More sharing options...
Oz07 Posted August 19, 2017 Share Posted August 19, 2017 Btw why don't you condense all these drainage posts into one?! Link to comment Share on other sites More sharing options...
Oz07 Posted August 19, 2017 Share Posted August 19, 2017 He's saying he's got to drop too much in 15m Link to comment Share on other sites More sharing options...
RichS Posted August 19, 2017 Share Posted August 19, 2017 On an extension I built some years ago I had a similar problem and I just used @Oz07 suggestion re. the backdrop. BCO actually OK'd the backdrop within the manhole chamber in order to save lots of unsafe, deep digging. Just had to put a rodding access within the chamber. Piece of cake. Link to comment Share on other sites More sharing options...
PeterW Posted August 19, 2017 Share Posted August 19, 2017 +1 to the backdrop Do it inside the chamber - 600x450 concretes are good for this - and use a tee with the top capped off with an access plug. Link to comment Share on other sites More sharing options...
Vijay Posted August 19, 2017 Author Share Posted August 19, 2017 (edited) 2 hours ago, Oz07 said: Btw why don't you condense all these drainage posts into one?! Just thought it would help if anyone does a future search Thanks everyone. The suggestion of speaking to the BCO makes sense and I'll see what he's happy with - would be brilliant if he was happy with the fall and can be rodded from both ends of the 15m run . I can go armed with a backdrop and see what he says about it. Wouldn't be too much trouble to do this and get what ever fall the BCO asks for: http://www.pavingexpert.com/drain05.htm Edited August 19, 2017 by Vijay Link to comment Share on other sites More sharing options...
Vijay Posted August 19, 2017 Author Share Posted August 19, 2017 44 minutes ago, PeterW said: +1 to the backdrop Do it inside the chamber - 600x450 concretes are good for this - and use a tee with the top capped off with an access plug. Chamber is plastic so I think I could do the same as the pic in my above post? Link to comment Share on other sites More sharing options...
PeterW Posted August 19, 2017 Share Posted August 19, 2017 That is an unusual backdrop but you could do that ..!! Link to comment Share on other sites More sharing options...
Vijay Posted August 19, 2017 Author Share Posted August 19, 2017 6 minutes ago, PeterW said: That is an unusual backdrop but you could do that ..!! I assume your suggestion was to have a concrete chamber? Link to comment Share on other sites More sharing options...
PeterW Posted August 19, 2017 Share Posted August 19, 2017 I've never seen an external back drop - they are prone to blocking at the base. Only ones I've seen a BCO sign off are where the pipe comes in at the side and then drops vertically to a 90 degree "shoe" that shoots it down the next section. No easy way to rod that if it does block at the elbow. Link to comment Share on other sites More sharing options...
Vijay Posted August 19, 2017 Author Share Posted August 19, 2017 Why do you say that, surely it can be rodded from both top and bottom inlets and the rod would reach to the bend?? Link to comment Share on other sites More sharing options...
PeterW Posted August 19, 2017 Share Posted August 19, 2017 You would have to rod "up" the rest bend so potentially compact anything blocked from above. In chamber back drops are easy to do and easy to service if they block. Link to comment Share on other sites More sharing options...
Vijay Posted August 22, 2017 Author Share Posted August 22, 2017 Desperately need some advice and guidance guys and girls. BCO came round and he's a really nice bloke who checked the foundation depth before. He is perfectly happy with the fall and said I would have no problems. Even when I pointed out the fall I have is 1:28 he was adamant that it is fine and I've worked things out wrong. He commented that cos it's in plastic, that things slide as Oz07 suggested. If it was clay it would be a different matter. HOWEVER I believe he's worked things out wrong cos when he explained it, he said for every metre you go out, you drop 40mm - but surely that's a ratio of 1:25? I said 3 times that I think he's worked it out wrong and I need a shallower fall but he insisted. The pipe run is 15m and I have a fall of 540mm between the IC and manhole. 15,000/540 = 27.78. If I want a 1:40 fall, then I need 375mm between the IC and manhole - have I worked that out correctly??? I'm going to send them an email to check again but it's awkward that I'm telling a BCO that he's wrong (if indeed he is), so am looking for any advice before I do Link to comment Share on other sites More sharing options...
Russell griffiths Posted August 22, 2017 Share Posted August 22, 2017 The way I see it is this 1:40 is as he said for every meter you drop 40mm so over 15m would be15 x 40 =600 so your 540mm is not far away. I stand to to be corrected but it's how I've always looked at it. Link to comment Share on other sites More sharing options...
Barney12 Posted August 22, 2017 Share Posted August 22, 2017 1:40 is "one unit of fall for every 40 units of run'. so if it was meters it would be 1m of fall in a 40m run. 1 Link to comment Share on other sites More sharing options...
Russell griffiths Posted August 22, 2017 Share Posted August 22, 2017 As @Barney12 said it's been a long day and my brains fried tonight. Ignore me please. Link to comment Share on other sites More sharing options...
Oz07 Posted August 22, 2017 Share Posted August 22, 2017 Don't send them an email you might show the bloke up and get his bad side. 1:40 is 25mm in a meter. 1:80 is 12.5mm in a meter. Just do do what I said. Run it at 1:40 and have one steep section between two ic's Link to comment Share on other sites More sharing options...
Barney12 Posted August 22, 2017 Share Posted August 22, 2017 (edited) 26 minutes ago, Vijay said: The pipe run is 15m and I have a fall of 540mm between the IC and manhole. 15,000/540 = 27.78. If I want a 1:40 fall, then I need 375mm between the IC and manhole - have I worked that out correctly??? Correct. A 1 in 40 fall would be 376mm over a 15m run. Don't worry about the 1mm though There is a nice explanation here with a nice calculator at the bottom of the page! http://www.pavingexpert.com/gradient_01.htm Edited August 22, 2017 by Barney12 1 Link to comment Share on other sites More sharing options...
Oz07 Posted August 22, 2017 Share Posted August 22, 2017 I have 20mm of packers taped on an old 800 level and do the same ratio to a 6ft level when I lay drains. When the bubbles right the fall is good 3 Link to comment Share on other sites More sharing options...
ProDave Posted August 22, 2017 Share Posted August 22, 2017 3 minutes ago, Oz07 said: I have 20mm of packers taped on an old 800 level and do the same ratio to a 6ft level when I lay drains. When the bubbles right the fall is good I do the same with a 25mm packer (offcut of tile batten) taped to a 1M level. Link to comment Share on other sites More sharing options...
Vijay Posted August 22, 2017 Author Share Posted August 22, 2017 Thanks for confirming that I got my calculations right. Good tip for the level, I'll do that I'm going to call him in the morning and have a chat, think it's the best solution cos he'll be coming back to check it anyway. Cheers for the link Barney Link to comment Share on other sites More sharing options...
Vijay Posted August 23, 2017 Author Share Posted August 23, 2017 Spoke to the BCO and then sent him this email: As per phone call, please find the figures I've used for calculating the drainage fall. The one we looked at at the front is 15m long and the invert between the two ends is 540mm. Using this site http://www.wyre.gov.uk/info/200316/building_control/166/basic_guide_to_calcu and using the calculator on this site http://www.pavingexpert.com/gradient_01.htm they both tell me the fall I actually have is just under 1:28. For a 1:40 fall I would need to reduce it to a 375mm invert and a 1:80 would need to be reduced to a 188mm invert. So over each metre that's a 25mm drop for 1:40 and a 12.5mm for a 1:80 drop So currently my fall is too much of a slope and needs to be reduced to a gentler fall which is why I had those ideas including a chamber backdrop. Their reply: Following a discussion between surveyors in the office and your email we can confirm we would be satisfied with the proposal as it currently is onsite and per information provided. From the information we calculate 1:36 fall which is acceptable as 1:40 is the ideal recommendation. However should you want to achieve 1:40 requirements which is optional, one end will need be raised or lowered accordingly to achieve the correct gradient. What do you make of that???????????????? Link to comment Share on other sites More sharing options...
Vijay Posted August 23, 2017 Author Share Posted August 23, 2017 I asked how they calculated and if I co do a backdrop and got this reply: Following talks with the surveyor an in chamber backdrop would not be recommended. We happy with the proposal as it stands currently. 1:36 was worked out by 540 divided 15 So I'm going with what they've said and cracking on tomorrow! Link to comment Share on other sites More sharing options...
Oz07 Posted August 23, 2017 Share Posted August 23, 2017 That was hard work wasn't it Link to comment Share on other sites More sharing options...
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