concrete footing and existing drains question

[bigdeano]

hi, got some plans thru to price up and on it there is something that ive not come across before, picture it if you can, dig down 1m for concrete footing right on the edge of the boundary to next doors, the inspection chamber and drain run is on next doors path (clients connects onto this run) about 800mm from the boundary but its approx 2.2m deep, on the plan it says to 'take down to a depth to aviod any transfer of load to drains', now me not being the brightest of lads is this abit extreme!, i mean a footing dug down 1m, poured with concrete and carrying a single story extension!, how much movement is there likely to be another 1.2m deeper and 800mm away from the new footing!!!, has anybody had to do the same?, has the inspector told you to do it this way??, sounds abit over the top to me, can i get away with a 1m footing as some of it will have to be hand dug!!!!

 

[noseall]

been there and done it.

//www.diynot.com/forums/viewtopic.php?t=130310

this photo shows a 2.4m deep excavation in close proximity to a 150mm sewer pipe. we ended up using 8' x 4' plywood shuttering and buried all 8' underground!

gotta be done laddie.

 

[bigdeano]

i can see why you had to go down abit more... but the drains we are dealing with are 2.2 deep and will be 800mm away from the trench we dig, will the inspectors still make us go down the full depth even though we are not exposing any pipework?

 

[noseall]

800mm is no hill o' beans i'm afraid, too close.

you will need to deep enough so that if you took a 45 degree line from the trench bottom and it intersected below the drain invert then you maybe ok.

as with any found's it will be b.c. who will ultimately decide.

 

[bigdeano]

hi noseall,
i kind of get it now, so its 800mm away from the trench and a 45 degree angle from the pipe would mean 800mm up from the bottom of the pipe, (2200mm deep pipe minus 800mm for the 45 degree angle from the pipe equals a trench depth of approx 1400mm) , does that sound about right!!, do we have to expose the pipe for the inspector or will he just lift the manhole like we did and work it out like this!!

 

[noseall]

possibly, BUT, be prepared for him to say "mmm, just go down a bit deeper eh, just to be sure".

we had a 3 tonne (jcb) on site, so just hoofed it out lower than the invert, knowing once the trench was dug there would be no way of getting the digger back over.

check with the b.c.o. first.

 

[wsdconst]

this is a problem we ve all had to deal with try talking to the building inspector and ask him if you can step the footing to this depth so you dont have to dig the entire footing below the invert

 

[bigdeano]

i think either way the minimum ive got to dig down is 1.6m and thats if the inspector says thats good enough, i just hope that when we start digging that there are no other pipes in the way,