Backfilling Around A 110mm Rest Bend

[Luke Walker]

Evening All, 

 

I just had a quick question regarding some underground 110mm drainage I am installing in my property. 
 

Currently I have excavated the entire ground floor in preparation for a 450mm insulated solid floor build up. 
 

As part of a full property renovation, I am laying new 110mm underground drainage. 
 

My question is regarding the back filling aspect for the rest bends of the drainage. The rest bends are 300mm in height. I understand the back filling element of the pipe runs needs to be in pea shingle as coverage, but what about the fill up to the crown of the rest bend? Is it a case of building the floor up as normal around the rest bend (type 1, sand, concrete etc) or should a full depth of pea shingle be used as backfill up the entire height of the rest bend (compacted) with a screed finish? 
 

Many thanks in advance 

Edited March 24 by Luke Walker

[Russell griffiths]

The rest bend MUST be bedded in concrete and have a concrete support and surround, it doesn’t need to come up high but MUST support the bend completely, pea gravel will not do this. 
if this pipe rises vertically the weight from the vertical pipe and the whoooosh of a big poo and the water falling over a couple of metres will smash into the bottom of that bend and can dislodge them or even completely blow them off the bottom of the soil stack. 
 

a very good job is needed here, if the rest of the pipe sits on the ground rather than in a trench then that need hunching up in a weak mix of concrete also, pea gravel is only for burying a pipe in a trench. 

[Luke Walker]

Hi Russell, 

 

Many thanks for your response. 
 

Fully understand your points re. bedding the rest bend and pipe in with concrete (was aware of this). 
 

I may not have explained my point clearly but what I was asking was once all of the bends and pipes are concreted in, when the solid floor build up is being installed (type 1, sand, cement, insulation, screed) … what is the process around the remaining neck of the rest bend and pipe? Do you build the floor up as normal around it or does it need to be shuttered off? 
 

Many thanks 

[Canski]

As long as it’s well supported like @Russell griffiths said then that’s all the support it needs. Carry on with the infill. I usually wrap some foam around the vertical pipe if it passes through concrete or screed. 

[Russell griffiths]

Oh ok, no sharp type one in contact with the pipe, build up in layers, bring the type one close to the pipe and fill around the pipe with pea gravel, another layer of type one and fill the gap with gravel again. 
be careful if you are using a whacker near the pipe. 
 

foam wrap around the vertical bit for the section that is in the concrete floor for wiggle room and fine location later. 

[Luke Walker]

Thanks so much both, 

 

Makes things much clearer now. 
 

Re. The ‘foam wrap’ - do you recommend a particular thing to use for this? 
 

Many thanks,