Drainage practical: down the trenches

[saveasteading]

Having spent 2 weeks in the trenches installing the drains, I am at your service for the differences between theory and practice.

After 40 years of designing drainage, but never afraid to get down there, I learnt a few things.

 

Also about Chemfloor.

Edited September 21, 2022 by saveasteading

[ProDave]

I feel this thread is crying out for pictures.......

[ToughButterCup]

You asked, I delivered.

[ProDave]

What they don't tell you:

 

You dig your trenches, lay the drains nicely set in pea gravel and leave the trench open for building control to come an inspect as they demand.

 

THEN you get torrential rain.

 

 

That photo is after the rain in the trenches had gone down a lot.

 

TIP:  Put your drain test bung in at the bottom and fill all the pipes with water so they won't float if this happens.

[ToughButterCup]

It was following your tip (Test bung above)  that caused the explosion in the photo further up this thread. Thanks, mate.

 

On a more positive note, I found this really helpful when working on your own ....

Oil filter grip  re-imagined

 

[saveasteading]

Some photos later. Lessons learnt first.

 

1. Supposedly experienced groundworkers don't necessarily know a lot. But they think they know a lot so don't read drawings or take instruction.

a) Ignore the gradients stated and put them in at 'on the line' of a spirit level for surface water, and 'over the line' for sewage. Or is that reversed?

b) Dig the depth that suits you and disregard the cumulative depth downstream.

c) Rodding junctions can face in either direction.

d) Joint lubricant is 'rubbish' and detergent is much better.

 

The 'professionals' were let go. The amateurs took over.

 

2. Plastic junction chambers have a drop of 60mm from the branches to the 'through' pipe. Thus there is a 60mm drop at the first junction and then at every 90 degree bend....we lost 240mm this way and that mattered a lot when digging deep trenches and the digester tank hole.. 'Level' chambers are available but not in stock.  (As I didn't know this, my previously lifetime of designed drains have obviously been fiddled in by 'joining the dots', and are flatter than intended.

This can be see in the ToughButtercup pic.

3. Plastic junction boxes are designed narrow to avoid children falling down them....even if screwed shut.

4. 300mm chambers have tight seals, but 450s wobble about unsealed.

5. a) constructing soakaway trenches is a pain. The membrane won't stay in place while the gravel is shovelled in.

b) perforated pipes want to return to the coil shape they came in.

6. People don't understand bulking of excavated ground. (a: Leave lots of room for the excavated material.  b) It won't go back in the hole however well compacted.

7. 'Nobody' puts down a proper slab for a digester, or levels accurately:  according to the digger driver (to whom multiple thanks for getting the tank in the ground, through skill and experience).

8. Some pipes simply slot into the socket while others need serious force.

9. 450 wide trenches may save money but some of us can't fit in them.

[Dave Jones]

good list, id add.

 

lose the spirit level and use a laser, especially over longer runs.

dig the trench using the laser to follow the slope to save on pea gravel.

chamfer tool to bevel pipe cuts.

silicone spray lube 

never use 4" ducting, its the work of the devil.

when running out of fall you can use 1/pipe diameter as a bare miniumum.

 

you have yet to experience the joy of using 63mm pumped chamber pipe. I wont ruin the surprise....

 

 

[ToughButterCup]

7 hours ago, saveasteading said:

...

6. People don't understand bulking of excavated ground. (a: Leave lots of room for the excavated material.  b) It won't go back in the hole however well compacted.

...

 

...and if you can, take the top layer of soil off, put that on one side of the trench, then dig down to the required level placing that spoil on the other side of the trench, like this

 

 

[ProDave]

For levelling, work out the fall you want per metre, then with a 1 metre long level, cut a bit of packing (wood) and tape it to one end of your level.  Then set the level (now jacked up at one end) for the bubble in the middle.  No guessing.

 

I think my treatment plant went in and back out of the hole 4 times until I got it properly level.

 

On sites I have been on, it is "surprising" how many professionals seem to "forget" the pea gravel and just put soil back in the hole onto the pipe that is propped up on a few bits of broken brick. 

[joe90]

4 minutes ago, ProDave said:

then with a 1 metre long level, cut a bit of packing (wood) and tape it to one end of your level. 

Great minds think alike!!! I did exactly that and it worked well. 👍

[saveasteading]

3 hours ago, ProDave said:

tape it to one end of your level. 

Yes we did that. Put on a long timber at dig stage, then directly on the pipe at laying. Plus we used an optical level for spot checks along the trench, for up a bit/ down a bit guidance...but that depends on the ability and willingness to do lots of arithmetic on the hoof.

Laser pipe level discounted for cost.

The designed levels went out of the window, to suit some fairly random stubs out of the building, and these drops at corners. ended up 250mm lower than designed, just working to the constraints and strictly to the falls required.

 

4 hours ago, ToughButterCup said:

take the top layer of soil off,

 

I don't know how often I said to do this.  Good for so many reasons.

 

3 hours ago, ProDave said:

professionals seem to "forget" the pea gravel and just put soil back in the hole onto the pipe

 

Ouch. as we were laying at 1:80 the gravel was essential. Quality control was exemplary, with no over-digging allowed. I was saying the opposite to our team, that a groundworker will use all the gravel available if the client is supplying it, and not worry about over-digging or over-filling. But perhaps that is better than shoddy work that will fail unless it is very steep.

It is worrying how little care appears to be the norm.  This appears to be worse in small scale domestic works, which is not where I come from.

 

Questions:

1. One pipe to install  , linking the final manhole to the digester tank. Is there any way of doing this with the connections all fully home? All I can think of is keeping the pipe slightly short and sliding back, but that leaves a gap in which stuff will stick.   I know it s normal, but perfection would be nice if there is a trick.

 

2. Sampling chambers seem to be very expensive  for what they are.   And we need it 1.8m deep.  where to find an offcut of large pipe, (or any other idea.)

 

[ProDave]

12 minutes ago, saveasteading said:

1. One pipe to install  , linking the final manhole to the digester tank. Is there any way of doing this with the connections all fully home? All I can think of is keeping the pipe slightly short and sliding back, but that leaves a gap in which stuff will stick.   I know it s normal, but perfection would be nice if there is a trick.

Make pipe in 2 sections the correct cumulative length to fit into their end fittings correctly, and join with a slip coupling.

[cwr]

4 hours ago, joe90 said:

Great minds think alike!!! I did exactly that and it worked well. 👍

Me too. I did mine with an old 10mm drill bit held to a 1m level with a rubber band. Level was marked every 100mm, so I could easily slide the drill bit to the gradient I needed. ie, for 1 in 60, move dill bit to 600mm mark.

[ToughButterCup]

3 hours ago, ProDave said:

.... and join with a slip coupling.

 

Ah, the delights of slip couplers.

It was yet another  fight with a slip coupling - on my own - in the wet - that I lost my temper.

 

And when I had done the necessary war dance to calm myself down, I realised that an oil-filter grabber was the thing to use to grab the washing-up-slathered-snake of a pipe. Worked like a charm.

 

Next time, I'll use two.

Did I say '...next time ... '  Phhhhhhhhhh..... Must be time to go down the pub. Coming?

[saveasteading]

17 minutes ago, ToughButterCup said:

slathered-snake of a pipe.

Yes it is slippy stuff: we used the official lube and it is even more so. As a single handed operation it required wiping off then a hand  application of sand (like home made swarfega) before any grip was possible.

 

I always thought of slip couplings as being for repair, and a little gap in-between the pipe ends was the accepted compromise.  The couplers we have used (Brett Martin) all had a central stop, which continues the running surface. But i see that Floplas don't have a continuous ring, but some tabs. Thus Floplas must all have a little gap (and object catcher) at each joint.  

 

Anyway, it does look like the best solution , with minimal gaps if the pipes are cut beautifully.

[ToughButterCup]

16 hours ago, saveasteading said:

...  if the pipes are cut beautifully.

 

I realised somewhat later than I should have done, that setting up for making routine operations easy is  very important .  Cutting a 4" pipe is easy - but it's not easy when

• you're wet and tired
• in the bottom of a trench
• have dirty hands
• on your own
• not sure you measured the pipe correctly
• haven't got the right tools easily to hand

I found that a super-jaws clamp is almost exactly the same working height as a scaffold end-step : that means you can handle long pieces of pipe on your own, and focus on making the cut accurately. You can comfortably apply washing up liquid, and then clean your hands off  before you jump back into the ditch.

 

A simple clean sheet of board lying next to you in the ditch so you can place and retrieve tools without clogging them up with clay is worth 10 times its cost.

[joe90]

3 minutes ago, ToughButterCup said:

A simple clean sheet of board lying next to you in the ditch so you can place and retrieve tools without clogging them up with clay is worth 10 times its cost.

That logic comes with age and maturity, I bet most of us (when younger) rushed into jobs, lost tools, slid about cussing and wasting time when trying to do it quickly, perhaps it’s because I am retired but I have found that better organisation and slower working ends up with less stress, a quicker job in the end and a better job 🥳 I had no stress during my build because of this attitude.

[saveasteading]

3 hours ago, ToughButterCup said:

Cutting a 4" pipe is easy

Have always used a saw but I was expecting there to be a tool for it, which would be worthwhile with 50 or so cuts to do. We wouldn't cut a copper pipe with a hacksaw when there are rotary cutters.

Or a saw guide big enough for a 110 pipe?

The slight variation I always get results in the longest dimension being against the stopper in the connection, and a gap elsewhere of 1-2mm. doesn't matter esp if away from the base.

But in a slip coupling situation the error is doubled and a likely catcher for any slow moving stuff, running out of energy.  Perhaps two factory ends would be wise.

 

ToughButterCup you appear to be testing a single pipe, hence testing the equipment. We had to do that as it failed after a few uses, due to its own hose connections (there are 6). A replacement kit works much better as it has more rubbery hoses.  How can that little collection of plastic (factory cost £5??) be so expensive at between £40 and £60?  The dearer one, though better, didn't include a water dripper, which is essential.

I guess most kits are used once and so out multiple tests were too taxing.

 

On 22/09/2022 at 08:10, ProDave said:

leave the trench open for building control to come an inspect as they demand

We invited them but they told us just to carry on, as they have since the start. We had sent some photos at various stages including pre-backfill drains, so presumably that was enough.

I wonder if they trust self-builders more than contractors, as it will be their own problem hence QC.

[Radian]

17 minutes ago, saveasteading said:

Have always used a saw but I was expecting there to be a tool for it, which would be worthwhile with 50 or so cuts to do. We wouldn't cut a

I used a chop saw with a TCT blade. Nice clean, square cut.

[saveasteading]

1 minute ago, Radian said:

a chop saw

Of course!  

[Radian]

I thought everyone did this. Always smells funny though, especially 63mm downpipe. Probably toxic fumes so best to wear a face mask.

[saveasteading]

4 minutes ago, Radian said:

I thought everyone did this.

I've never seen it. I guess chop-saws don't fit well on large muddy sites, which have been my territory.

Groundworkers just get out the disc cutter for everything.

[Mr Punter]

I cut and chamfer with a cordless 4" grinder.  Mark the cut with a rubber band and a sharpie.

[saveasteading]

1 hour ago, Mr Punter said:

a cordless 4" grinder. 

I think the one we used was too powerful as it ripped through the plastic very quickly, and we ended up with a series of slices.

Then straightening and bevelling was easier.

Also the DeWalt doesn't appear to allow right-handed use, according to the proud owner.  Improved with practice of course.

[joe90]

I used an old socket end with the rubber removed as a guide and a handsaw, flapweel on angle grinder to chamfer..