What's the deepest you should hand dig a footing trench?

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Hi!
I'm looking to build my front extension - unfortunately due to a pesky public drain my footings need to be 1.7m deep (150mm below invert within 3m)!. I have received a quote from a ground worker for £6k to do the work including concrete fill and muck away. The footings are approx. 0.6mm wide x 1.7m deep x 10m long.

I hand dug the footings at the rear (0.6m wide x1.2m deep x15m long) mainly due to poor access so I'm considering doing it again out the front.

Has anyone hand dug such deep footings?
Am I mad?
How can I do it safely - is it even worth it? OSB boards with supports between? I'm guessing it will be hard work throwing clay out of a deep trench...
Does the groundworkers price seem OK - I'm happy to delay works until next year to see if prices drop a little (although they may not!?)

Thanks...
 
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Over 1.2m requires shoring up, my drains were 2m and we used any sheet material we had with 2x4's cut to prop it in place worked ok but if had went wrong wouldn't of ended well.

As for getting the spoil out we sloped one end so we could walk out with the majority of the spoil then just had to mess about squaring off the one end before pouring.

IMG_20210624_142135.jpg
 
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Have you challenged the requirement for that depth? Eg a drain 3m away would not be influenced in the same way as one 300mm away.

Can the foundation be stepped?
 
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Over 1.2m requires shoring up, my drains were 2m and we used any sheet material we had with 2x4's cut to prop it in place worked ok but if had went wrong wouldn't of ended well.

As for getting the spoil out we sloped one end so we could walk out with the majority of the spoil then just had to mess about squaring off the one end before pouring.

View attachment 275153

Good idea about the slope! I was thinking of getting some OSB and having wood between. I guess the osb can stay in for the pour? Or quickly whip it out before hand.

Did you use wood right the way down or just at the top part of the trench? Ie first 1.2m so OSB could be on its side...
 
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Have you challenged the requirement for that depth? Eg a drain 3m away would not be influenced in the same way as one 300mm away.

Can the foundation be stepped?
Thanks Woody - Yes I have phoned them and they are insisting no drain within 500mm which is fine. Unfortunately they are still insisting any footing within 3m must be 150mm below invert. Seems crazy to me. I still need to have a site meeting with building control but I guess they have to follow the water companies rules?

Building control via the phone mentioned something about a 45 degree rule so a 1m footing 1m away from the drain would be fine. Need to get them on site and have a chat. Doubt the water co would go digging around to see how deep my footing goes once its in!
 
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Then you need to escalate this to a complaint.

The water company can't just make things up for random reasons as this then creates unnecessary expense for customers for no reason and can be construed as denying them access to services.

Their policies on foundations are intended as a catch all guidance. The actual requirement is not to potentially damaged the public network.

You need a reasoned explanation, which you could then counter with your own reasoned explanation - via a more qualified person than the admin clerk at the water company if need be
 
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Whatever depth you're going to dig, hire a mini digger for a week.
It will be the best money you've ever spent.
It's not difficult to operate, just spend some time in an open space getting familiar with controls.
My wife learned to use it confidently in half hour or so.
That made my day great when we built our extension.
Wife on the mini digger, me sitting in the shade with an ice cold beer in my hand.
 
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I only used osb at the far end where it was down to 2m,you need to hope its been dry for quite awhile when you start to dig, once you get to about 1.5m it doesn't take a lot for it to collapse in, you certainly need to make sure someone's working with you even if there just spotting for ground movement, if it goes with you in it on your own the outcome may well be fatal, digging at that depth is a serious game
 
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So the blurb on Southern Waters website says

"If you are constructing a new building, the first thing is to check if it is subject to the Building Regulations. If it is then you are required to confirm it meets the standards set out in section H4 of the Building Regulations and this can be assessed by a Local Authority Building Control (LABC) department or an independent approved inspector as per your choice."

H4 says...

pipe-runs.jpg

I will be more than a meter away from the drain - House footings are 1.2m deep anyway (ie more than 750mm)

Southern Waters letter says - a) No structure (footings, walls etc) running within 500mm of the existing 150mm vitrified clay (VC) public foul sewer/manhole will be permitted. b) Where within 3.00 metres of the sewer, foundations must be taken minimum 150mm below the invert level of the sewer/manhole.

Totally bonkers. I will book a site meeting the building control as I may be worrying about nothing at the moment!
 

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