Treatment plant, concrete base

[Welsh-border]

About to install Graf one2clean treatment plant, 5person 3750 litres. Looking for recommendations re concreting base, how much concrete? Fairly high water table, don't want it to float out.  

 

[JohnMo]

The install instructions normally give you good guidance based on your ground condition, they will also stipulate what you need to use for back filling.

[ProDave]

I did not use a concrete base, that would have left the hole open for longer while you poured a base and waited for it to set all the time filling up with ground water.  So I just set mine on the ground in the excavated hole and started pouring concrete.  

 

You must progressively fill it with water as you pour the concrete but without getting the water level at any time significantly higher than the concrete level.

[Russell griffiths]

You don’t need a concrete base, in fact it could be a pain in the arse, if you set it too high you cannot wiggle the tank down. 

I have a graff and I bet I have a higher water table than anybody on the forum. 

 

Put 200mm of 10mm gravel in the bottom of the hole, bed your tank into this and get the correct height and level. 

Fill the tank with clean water 50% full

back fill around tank with dry concrete mix, absolutely dry, so you can walk around it compacting it, get up to the half way mark and start adding more water to the tank up to 75% full, add more concrete around tank but this time a bit wetter, bring up to whatever level your happy with, as I said my water table is horrendous so I concreted right to ground level. 

[saveasteading]

When the tank is under the water table, presumably so is the soakaway and the feeding  drainage system.

Do the pipes just slowly release treated water due to  the surcharge of your drains?

[saveasteading]

But back to thd question...gravel underneath is a good compromise as something to lay the tank onto, to a prepared level and  that will spread the load.

We were precise about getting the tank level. The digger driver said he had never seen anyone bother to get one level. Also that he had lifted in many tanks and had never seen a concrete base....we used gravel.

[nod]

I used about 3 cube at our last one and six cube at our current build Half way up the tank is ok 

Make sure you fill it to the brim with water once in position 

Ive seen them Bob up like a cork the following day 

[Iceverge]

We used a concrete precast tank. 

 

Hole dug, base levelled with gravel, tank dropped in and connected, backfilled with earth.