Cobcrete slab - fill trench after water main install

[NorthWest1]

Hello,
Just trying to get some advice on filling a trench in a concrete slab. I have to replace my lead water pipe and am looking at giving it a go myself. Was originally going to just come under foundation and stick it behind front door area ( well, in corner, to side of door ), however, my gas pipe is under the stairs and on that very same wall and I reckon I might find that runs out to the pavement and blocks me coming up with the 4'' ducting. I'll have a little exploration look first but if it is, I'll have to run the water pipe somewhere else and finish under the stairs ( which would actually be neater ). It's a 1930's slab with bitumen and parquet, I'm assuming there is no DPM, other than the bitumen. If I trench say 150mm wide, what is the best way to fill it afterward, is it just shovel the soil back in and pour 4'' ready-mix concrete, will it actually adhere itself to the rest of the slab ?

 

[cdbe]

Surely there's a way to avoid all that. Have you looked at insaducts?

 

[NorthWest1]

I should have clarified, the trench won't be going through the parquet floor, that is in living room. The trench, about 2m long would be going through 1m of quarry tile ( red square tiles ) behind front door and then a 1m length of concrete under the stairs. I'm just hesitent to go cutting through the slab. The whole floor is getting an asphalt covering down the line, so the parquet is getting ripped up anyway but I was planning on going straight over the quarry tiles. These concrete floors are a nightmare, damp, uneven and you can't do anything with them, I wish I had floor boards.
The Insuduct might be a viable alternative, so long as I can come up past the gas pipe outside the front door, the space for the isuduct box is limited. I'll look into it,

thanks