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Pumping Enigma


Ed_MK

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Houston ...we have a ...

(well you know what we have)

 

Basically the engineer working for Anglian water came out today and checked the falls.

 

(If you know already ..i wont bore you ...but we are running all the services through our inlaws house to the road in front
of their house as the road we have an entrance on the services are "unadopted" ....long story .....but)

 

...anyway. Due to the distance of around 45m from main sewer to our invert ...we have to fall TOO far..

...and it would be a smidge under 2m deep along the house which is too close for comfort ...without underpinning

which is financially a non starter

 

..so someone suggested a pump ...! ...sounds good ...

 

But of course we are ALSO picking up our inlaws waste when we run out to the mains sewer ...as that was part of the deal

(they are currently on an old and dilapidated rear garden cesspit)

 

So my question (which even the waste company couldn't answer) is ...

 

Will my pump a the proposed location effectively SHOVE the waste out to the sewer when it HAS to pass through 
our inlaws manhole as well ?

 

any Pump Gurus online ?

 

see attached for a handy pic 

 

 

pump_problem.jpg

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I can't see the pump working that close to your house.

 

As I understand it, the pump raises it a bit, and from there it falls by gravity to the sewer.

 

So more typically it would flow by gravity from your plot to somewhere on your in-laws house, possibly just behind their house, from where it would be pumped up into an inspection chamber at a higher level from where it flows by gravity into the sewer.

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Sorry - who’s said 2m deep needs underpinning ..??

 

What is the in-laws invert level and the sewer invert ..?

 

you could run at 1200mm all the way to the in-laws, pick them up at that depth and run to the front gate, drop to 2m over 2m which is fine and then go 1:60 into the sewer. 

 

If if you are pumping then you still need the fall to the sewer from the in-laws and would need a very good sealed intercept for the pump outlet. 

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hmmm. i see.

 

well the inlaws are currently on a 40yr old cesspit in the rear garden ...so their current invert level isn't deep at all ...around 450mm down!

whilst the main mahole in the road is 2.7 metres down ...but again the road surface is about 500mm lower than their land ...so in total
the fall from theirs would be over 3M and the distance is about 25M from their invert to the main manhole ...so QUITE a fall !!

 

the plan was to dig theirs deeper and i would originally connect to them and then fall out at a respectable 1:60 to the road.

 

Regarding the under-pinning ...the team that came estimated for plan A ...(normal pipe run) to work with a decent fall when the trench

had to go along our inlaws house it would be falling at between 1.5M and 2.0M deep and due to the space between their house and a neighbours 

garden wall (2M gap ..it would be TOO deep to be so CLOSE as the trench would be almost 500mm away from the in laws exterior wall which they
estimated at 600mm foundation deep) and so would be BELOW them and potentially unsafe..if that makes sense

 

attached pic should help

 

the challenge is the highlighted line in regards to the zig-zag (section close to building)

the things i CANNOT change are

 

A - my invert
D - Anglians invert

we can "play" with anything else but where it gets close to the in-laws house, i don't really want to risk undermining, and we only have 
2m gap to play with ..and at least ONCE i hear them talking about the "angle of repose" ... which as we know is always a bad phrase

I am told

 

 

falls.jpg

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So work it back. If your invert starts at 450mm, and follows a 1 in 80 fall down your in laws garden, how deep would it be by the time it got to the gap between the 2 houses?  Unless I have done something wrong, I make that 0.825M deep, so you could probably make that 1M deep and have a bit more fall on the run down their back garden.    1M deep should not bother their foundations.

 

The run from there to the drain will have to be a lot steeper, there are methods to do this but I don't know about them, drop chamber being one I hear about.

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Making this too hard .....

 

Start with your invert at 650mm below FFL. From there, you’ve got a 1:60 for 35m to in-laws IC so the invert here is now 1.2m give or take. 

 

C to D is now a 1.5m drop over 20m which is fine - it doesn’t need a backdrop or anything else, and if they want you could drop level with a 45 degree section if needed and the last bit would be 1:40 into the sewer. 

 

And whoever is telling you that you cannot dig a 300mm wide trench within a 2m gap at below founds level is talking bollocks. Foundations don’t just slide into holes - if they plan it properly then it will be fine as you use 6m lengths of UPVC and joint them before they go in the trench so no one is working below ground. Level

sticks make sure you get the falls correct. 

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The foundations thing.

 

It is generally accepted that the load on the foundations extends outwards and downwards at 45 degrees.

 

So if the foundations are 600mm deep, and you dig on the centreline between the 2 houses, so 1 metre away from each house, then that load bearing area would be virtually 1.6M down anyway so you are not going to disturb that in any way.

 

A little less in practice as you project the 45 degree line from the outer edge of the foundation, so it depends how wide the footings are.  But in any event digging at 1.2M is not going to bother anything.

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Yes, that 45 degree down from the outer edge of the foundations is a worst case critical angle of repose for soil (bearing in mind that the critical angle of repose is measured upwards from the lowest horizontal point, i.e. the base of the trench).

 

The critical angle of repose for soil ranges between 30 deg and 45 deg, so as a downward angle from the foundation, measured relative to surface level, the angle translates as between 45 deg and 60 deg for normal soil.  For something like compacted clay the angle is much steeper, and can be near vertical, as seen below in the up to 2.5m deep excavation we did in order to level our plot.

 

57418e08a60ef_Thehole-Nface.JPG.30870a50dd256e8bef7a43a12cc27afa.JPG

 

 

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Firstly, your invert of 1.6m seems rather deep.  Are the drains on you side already laid? If not, see if they can be shallower, as I would normally expect them to start at about 0.6m, so the additional metre on yours suggests a very long run (60m?)

 

Avoid the pump station as it is lots of additional cost and a nightmare when it fails as you will win the prize of a tank of raw sewage.

 

Excavate the drain run at a fall of 1:60, picking up the in-laws drain on the way (this may be via a bottom outlet inspection chamber).

 

If the main Anglian sewer is over 300mm dia you may be able to connect via a saddle connection on the top of the pipe.

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Well perhaps the workers that came (Anglian subcontractors) were doom and gloom,

but sadly they put the willies up my father-in-law :( with all the talk of subsidence, underrmining, underpinning

et al !

 

I drew it out roughly to scale below ...but as i have no experience in civil engineering, does it look 

like a chilean mining disaster waiting to happen ?

 

I mustb admit when 3 irishmen are stood around a laser level repeating as a mantra

"its deep, maybe too deep Pat"  ..."oh its deep alright Mick, very deep" ..."what do you think Michael"

...."it's a deep bas*** alright boys" 

 

etc

 

etc

 

trenchsideview.jpg

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I think what everyone is saying is don’t go to 2m past the house - go shallower and then drop to the sewer at a steeper gradient from the in-laws onwards. 

 

It also wasn’t clear that you wanted to put a lot more in the one trench - again, good reason for going shallower by the looks of it. 

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I am afraid that the Party Wall Act will come into play here.

 

Although your sketch is neat it does not show the foundation and trench depths accurately. If the footings are 600 the trench should be over 3 times as deep as they are.

 

Can you let us know why your drains are so deep?  If they are already in place it may still be simpler to dig them out and re-lay them at a shallower depth.

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Groundworkers were  tools basically!

 

and after stating the footings would be 1m of concrete

changed his mind and set them for 600mm

 

he said his 1m (included the trench block) which it didnt in my original plan

..needless to say we got into a big ruck and he demanded more dosh if we wanted 1m and so we had to settle at 600mm

foundation pour

 

Thing is the house now sits 400-600mm lower than planned and what was a LONG fall at 1:60 to get to the inlaws invert

now means we are below their invert already buy about 200mm

 

so we need to lower their run so we can feed into it 

so even with a shallow fall 1:80 tops we will be 1500mm down by the time we get to them

 

1:60 would leave us closer to 1800mm 

 

does that make sense ?

 

 

We could easily run out at 1:60 to the road as the sewer is so bloody deep , but somewher along the line we havbe to 

 

1. Fall a fair bit as the council will only allow a connection at invert level

2. Pick up the inlaws waste ...as if it wasn't for them ..none of this would be possible ...so i cant just sail past 

leaving them on a leaking cesspit 

 

 

Edited by Ed_MK
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36 minutes ago, Ed_MK said:

Groundworkers were  tools basically!

 

and after stating the footings would be 1m of concrete

changed his mind and set them for 600mm

 

he said his 1m (included the trench block) which it didnt in my original plan

..needless to say we got into a big ruck and he demanded more dosh if we wanted 1m and so we had to settle at 600mm

foundation pour

 

Thing is the house now sits 400-600mm lower than planned and what was a LONG fall at 1:60 to get to the inlaws invert

now means we are below their invert already buy about 200mm

 

so we need to lower their run so we can feed into it 

so even with a shallow fall 1:80 tops we will be 1500mm down by the time we get to them

 

1:60 would leave us closer to 1800mm 

 

does that make sense ?

 

 

We could easily run out at 1:60 to the road as the sewer is so bloody deep , but somewher along the line we havbe to 

 

1. Fall a fair bit as the council will only allow a connection at invert level

2. Pick up the inlaws waste ...as if it wasn't for them ..none of this would be possible ...so i cant just sail past 

leaving them on a leaking cesspit 

 

 

Can you not put a backdrop IC in where your pipes join up with your in laws to bring them down to your level?

 

I'm in a similar situation, I join the neighbours manhole about 900mm below so intend to dig it all out and put a backdrop in.  This then runs the final 5m to the sewer which is at an invert of 3m. 

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38 minutes ago, Ed_MK said:

Groundworkers were  tools basically!

 

and after stating the footings would be 1m of concrete

changed his mind and set them for 600mm

 

he said his 1m (included the trench block) which it didnt in my original plan

..needless to say we got into a big ruck and he demanded more dosh if we wanted 1m and so we had to settle at 600mm

foundation pour

 

Thing is the house now sits 400-600mm lower than planned and what was a LONG fall at 1:60 to get to the inlaws invert

now means we are below their invert already buy about 200mm

 

so we need to lower their run so we can feed into it 

so even with a shallow fall 1:80 tops we will be 1500mm down by the time we get to them

 

1:60 would leave us closer to 1800mm 

 

does that make sense ?

 

 

We could easily run out at 1:60 to the road as the sewer is so bloody deep , but somewher along the line we havbe to 

 

1. Fall a fair bit as the council will only allow a connection at invert level

2. Pick up the inlaws waste ...as if it wasn't for them ..none of this would be possible ...so i cant just sail past 

leaving them on a leaking cesspit 

 

 

Generally speaking foundations are 1m deep with a min off 450mm of concrete   Did you have a structural engineer design your foundations? And did you set them a datum level to work too? 

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Yes ...and i think its what we have settled on after talking to Anglian Water contractors

 

Basically on our side of the fence will be a 3in Single Pump (solid handling at 65%)with a 1000L tank, guide rails and Automatic Alarm 

the outlet will be at 500m below DPC it will feed into 90mm pipe and run 30 metres down the wall of our in-laws into 

a new manhole that they are installing and then gravity out to the main sewer a further 25m

 

this will mean we can fall gradually to a trench that will only be a metre at MOST (if that) at the inlaws corner ..(which is well past the narrow between houses)

I am getting prices of between £1500 and £2300 for this setup (almost identical) ..including all the fittings to take 2 x 4" waste feeds and am told i basically REPLACE the planned
manhole wit this station ..and away we go!

 

I cant work out why the costs vary a bit ....but i do know that a 50m roll of 90mm drainage pipe is lot of money 

 

anyone got any advice ....

 

 

(or a coil of 90mm!)

 

:)

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On 28/01/2019 at 18:45, Sam Thomas said:

Generally speaking foundations are 1m deep with a min off 450mm of concrete   Did you have a structural engineer design your foundations? And did you set them a datum level to work too? 

 

engineer said on our ground 600mm would be adequate ....but we KNEW we sat low and wanted to basically minimise site waste AND make sure we were high enough for
a long flow..so ASKED for a 1000mm "foundation"

 

( i KNOW they KNEW very well what we meant, and WHY we were doing it ... and we had a datum on the site too) 
 

But when it came to the pour we were told that the 1000mm we were quoted for wasnt 1000mm of concrete it included the base block and kick brick and these are 400mm and so based on OUR datum we are now 400mm BELOW where we thought ...

 

So ..we have 60+ tonne of subsoil to move about

....and are now pumping up

 

(sigh)

 

It's done and dusted and I cant go over the old argument ...needless to say get any term clearly "defined" in writing...but now it is what it is

 

 

 

Edited by Ed_MK
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Sorry ..me again!

 

does anyone know why the suppliers say  am better running the 90mm pipe to the manhole 37M away ?

If i was to Boss it up to 110 it would be a quarter of the price ...I take it they have their reasons ?

 

 

(apart from getting another 400 notes from us)

Edited by Ed_MK
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Pump station specs  are nightmare to evaluate..
 

*Some systems are quoted as 3in when they are actually only 2.5" systems with a 3" 

external pipe outlet!..the terminology used is often "kitted to 3"" or "discharging through 3"" with
no mention of the ACTUAL pump diameter anywhere ....bit naughty

 

*Alarms are included on some ...but not others ..."Alert indicator" sounds fancy ...but its not an alarm its a red light on the pump
to show its getting current

 

*Guide rail and Guide Chain!?! are not the same as they seem ;) ..Guide "chain" is just a bloody chain 

 

* Tank sizes are often quoted to discharge height which is how you would want it, i mean if its over that ...its knackered
 ...but often you will hear "brim capacity" which means basically to overflowing 

 

I have 4 quotes in front of me ...so I will make a decision on Monday 

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90mm will be 90mm MDPE that runs at positive pressure - not unreasonable to get 2-2.5bar on those pumps that could blow 110mm joints apart. 

 

Surprised they say 90mm as most use 63mm. 

 

If you need advice, speak to MPC Services in Ripley who do all this sort of stuff. 

 

Has BCO signed off the size of the tank and the pump ..??

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