Sewage treatment plant, in bad ground

[Russell griffiths]

Morning I’ve just finished fitting my treatment plant, which turned out to be a major engineering project, the first attempt was abandoned due to high water table and we had to look for some advice and hire in some more kit, it all went according to plan the second time although it was a fight every second of the job, if anybody is dealing with bad ground or high water then shout out I think I’m probably fairly clued up now on a good process. 

[ProDave]

Oh more photo's and narative please.

 

I assume it was a case of pump the water out, then get the plant and concrete in quick?

[ToughButterCup]

Love ya digga man .... 

I think our water table is similar to yours, but your ground looks problematic. We used wooden shuttering for a while, but I gave up on that: unwise, but we were lucky.

 

Being the courageous man I am, sent SWMBO down the 'ole to see how deep it was ?

As you can see, the shuttering was a little on the light side. And I did bring her a cup of tea while she was down there.

 

It was the one job with a digger that truly scared me. Had I used your shuttering system, it would have been so much easier.

 

I chained concrete fence posts to the edge of the tank (to act as ground anchors) , lowered the assembly  in, and then concreted the lot in. Years later my shoulders still ache from that job.  (Couldn't get a mixer lorry anywhere near it)

[Russell griffiths]

1 hour ago, ProDave said:

Oh more photo's and narative please.

 

I assume it was a case of pump the water out, then get the plant and concrete in quick?

Sort of but not quite. 

Pumping the water out just caused it to fill back up, 2inch petrol and a 3inch diesel pump flat out kept it out, but if one turned off for a minute it rose a foot in the time it took to fill the tank back up. 

 

In the end we pumped it to 150mm deep and installed 2 electric pumps in the bottom. 

Now the funny bit, I left the electric pumps running as I tipped in the concrete and they where still running when I finished, I then turned them off and cut the power cables, so they are still in the hole at the bottom. ?‍♂️?‍♂️

Oh well they where only £75 each so small cost in the grand scheme of things. 

[ProDave]

So I take it the shuttering is also now encased in concrete and is another "consumable"?

[Conor]

Hope you've done your flotation calculations ?

[Russell griffiths]

1 hour ago, ProDave said:

So I take it the shuttering is also now encased in concrete and is another "consumable"?

No bloody way, that stuff was eye wateringly expensive to buy. 

All pulled out cleaned and returned to hire depot. 

[Thedreamer]

2 hours ago, Russell griffiths said:

Now the funny bit, I left the electric pumps running as I tipped in the concrete and they where still running when I finished, I then turned them off and cut the power cables, so they are still in the hole at the bottom. ?‍♂️?‍♂️

Oh well they where only £75 each so small cost in the grand scheme of things. 

 

In the far future there will be a post here asking what those pumps are for!

[Russell griffiths]

1 hour ago, Conor said:

Hope you've done your flotation calculations ?

Fag packet calculations 

4500 kg of water in tank

6000kg of concrete. 

If it floats I eat one of my smelly socks that was in my wellies all week. 

[Mr Punter]

Before you pumped it out, was the water the same level as the gravel pit lake?

[Nick Laslett]

These pictures look all to familiar! My ground workers had two attempts at the STP install. High water table and running sand were the problems. First digger didn’t have enough grunt to get the shuttering all the way in. First hole was completely abandoned and a second attempt in a different location with a much larger digger was successful. The first day of the second attempt the digger hydraulics failed!

 

 

[Russell griffiths]

@Nick Laslett I took my advice from a lad that works in running sand, he gave me the pointers about the trench box, I did consider sheet piles but they would have needed a bigger excavator, like you found out. 

 

@Mr Punter water in my hole was lake level, the only good bit is that the water would not normally be there unless you dig a hole, the ground actually drains really well to the lakes, so as soon as you fill the hole in the water finds another way out and the ground firms up very quickly. 

[DragsterDriver]

Ffs did This at the weekend. A Graf sewage plant- ignore the instructions it CAN be wet installed in concrete. I had an absolute fail with sheet piles and a 5 ton digger.

[Russell griffiths]

12 hours ago, DragsterDriver said:

Ffs did This at the weekend. A Graf sewage plant- ignore the instructions it CAN be wet installed in concrete. I had an absolute fail with sheet piles and a 5 ton digger.

What’s up ? Have you sussed it. 

Mines a Graf. 

[DragsterDriver]

5 minutes ago, Russell griffiths said:

What’s up ? Have you sussed it. 

Mines a Graf. 

Yep sorted now- tried the dry install they recommend and a complete waste of time and materials. Contacted them and they’re fine with a concrete install “It’s just not in the literature because it’s German”.

 

the tank popped up like a U boat.

[markc]

the tank popped up like a U boat. ????

Just spit my tea out

Edited September 30, 2021 by markc

[Russell griffiths]

1 hour ago, DragsterDriver said:

Yep sorted now- tried the dry install they recommend and a complete waste of time and materials. Contacted them and they’re fine with a concrete install “It’s just not in the literature because it’s German”.

 

the tank popped up like a U boat.

Did you have it full of water. 

[ProDave]

2 hours ago, DragsterDriver said:

Yep sorted now- tried the dry install they recommend and a complete waste of time and materials. Contacted them and they’re fine with a concrete install “It’s just not in the literature because it’s German”.

 

the tank popped up like a U boat.

Yes seen that happen.

 

We were badly advised at our previous house and the tank is in pea gravel.  It is not an issue when full, but it means we ONLY get it emptied usually in the spring after a long dry spell when we can be sure the water table is low, and then immediately refill it with fresh water.  that would probably "surface" if we emptied it in winter.

[DragsterDriver]

2 minutes ago, ProDave said:

Yes seen that happen.

 

We were badly advised at our previous house and the tank is in pea gravel.  It is not an issue when full, but it means we ONLY get it emptied usually in the spring after a long dry spell when we can be sure the water table is low, and then immediately refill it with fresh water.  that would probably "surface" if we emptied it in winter.

 

I had my reservations but didn’t want to void the warranty. Turns out it doesn’t - so it’ll be filled with water and lean

mixed backfilled as usual.
 

 

36 minutes ago, Russell griffiths said:

Did you have it full of water. 

I had it half full 2400 litres, their spec is 1/3 full 1600 litres. Gravel bed, shingle backfill- maybe 16t in all.

 

[DragsterDriver]

2 hours ago, markc said:

the tank popped up like a U boat. ????

Just spit my tea out

I’m not kidding either ? it had surfaced by about 1.5m when I pulled up on Monday. Felt like crying but it was proper funny!

[Russell griffiths]

1 hour ago, DragsterDriver said:

I’m not kidding either ? it had surfaced by about 1.5m when I pulled up on Monday. Felt like crying but it was proper funny!

This is the only job in my entire life when I wanted to just lay on the ground and cry, every step was like fighting a war with Mother Nature. 

[DragsterDriver]

2 minutes ago, Russell griffiths said:

This is the only job in my entire life when I wanted to just lay on the ground and cry, every step was like fighting a war with Mother Nature. 

“you weren’t there man”

 

Yup- I knew....I just knew it was tits up but worked until 7pm Saturday....but I knew. 
 

sheet piles.

pumps.

the horror.