Manhole cover in garden

11 Aug 2010
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United Kingdom
Looking for some advice please

At the bottom of our garden we have a waste water manhole cover surrounded by about a foot or so of concrete.

It is also raised off the floor by about a foot or so as well.

(see attached pics..)

We're wanting to get it lowered and/or reduced in size as its a bit of an obstacle when trying to get in or out of the driveway and mainly as we're considering getting our drive tarmac'd or paved as its a bit of a mess and this is in the way..

We've been told by United Utilities that we need to cough up for a contractor who is trained for working in Confined Spaces. (Not quite sure why?)

Is this really needed just to reduce the height and size of the concrete surrounding the cover?

Assuming it is, where would we start to look to track someone down to give us a quote?

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It does'n't look "confined" to me. Any decent local builder should be able to sort it.
Is it shared with other neighbours? If not and it's on your land then it's yours to do with as you please.
It overlaps the garden by a couple of inches, also when we lifted the cover, water from both houses can be seen flowing - so yeah it's definitely shared.

Which puts us in a dilemma as I'm not sure we can touch it...

As for the requirement for confined spaces, I'm wondering if UU feel they need to go IN the shaft - which I highly doubt anyone would need to do just to lower it to ground level.
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Looking at the pic, it's likely the chamber is built with 9" brickwork, and a cast slab on the top. To lower would probably mean removal of the slab, chop out brickwork as required and recast slab at appropriate level.

I agree with Nozzle, to cast slab would need shuttering built in the pit, then it's removal once slab has gone off, so at some point someone would have to be working in the pit, which is classed as a confined space.

I would have a look for a drainage or groundwork company and ask them to quote, assuming UU will allow you to carry out the work. As it's possibly UU's asset, they may insist they carry out the work (or one of their approved contractors is used) and you foot the bill. Either way, would also be advisable to upgrade the cover to one that will take a driveway loading, the current cast iron cover may well break with the weight of a car going over it.
Thanks for the clarity regarding the H&S regs

As for the chamber, it is only about a max of 2 inches bigger than the cover (which is 1.8 ft Square - meaning the chamber is probably just over 2 foot square) - the concrete slab is ft 10 Inches square...

The cover looks really old and is starting to rust badly - in fact the housing for the cover is loose from the concrete cover

From what UU said they seem to want us to find a contractor who then has to get in touch with UU to carry out Risk Assessments, etc - though I would have thought they'd have their own approved and insured contractors themselves....
I would speak to UU and ask for the names of several contractors on UU's 'Approved Contractor' list, or people who have worked with them before and would be able to undertake such a job.

I suspect UU's contractors rarely carry out work on a scale as small as that, usually sewer jobs cost thousands, if not millions! :eek:
I'm guessing that these front drives have evolved from walled in front gardens and that folks have opened up their frontages to parking. The ground level on these front gardens would have been higher.

However, I find it difficult to reason why such a large 'biscuit' was used to slab over such a small chamber.

If the chamber is of similar size to the lid, then there is no reason why the surrounding concrete could not broken away and the whole thing re-hashed. All the work could be done from above with the lid and frame mostly intact, until reaching it with the breaker.

Are you sure there isn't a large bore chamber beneath?
@Hugh Jaleak - Hopefully they wont want that much just to break up a slab of concrete and put a new, lower / smaller one in its place :eek:

@noseall - Some of the bricks have fallen out at the front near the pavement (will try get a pic tonight) and from what I can see there is nothing between the edge of the concrete slab and the actual chamber wall - so there is nothing larger than the chamber itself with this concrete monstrosity sitting on top of it and patched up with loose bricks and rubble

@HERTSDRAINAFE2010 - Not sure a but at a guess I'd say its somewhere between 7 to 10 foot deep =- again I can get a pic tonight if needed.
Pics are always useful. I would think biggest issue is going to be breaking up the existing slab, and removing brickwork whilst avoiding detritus falling into the chamber below. (Any that does would need to be removed ASAP!)

Condition of brickwork may determine what needs doing, if it's in particularly poor condition then UU may insist this is addressed at the same time, which could make the job much more complex than you anticipate. :cry:
1. I would estimate that the drop from the top of the slab to the neighbour's driveway surface is 20" - 24".

2. This drop will have to be taken into account when detailing any new manhole level, and any extension of the driveway dividing wall.

3. Directly across the street they also have a drop between driveways.

4. There are signs on the road of the surface having been made good, signs that would indicate fairly recent drainage work - perhaps, lateral sewer replacements?

5. I should imagine that you will just about squeak inside your property line if you drop the manhole cover to your driveway level.
But, first, indicate on the slab surface your manhole chamber dimensions - use chalk or crayon, and then pic to here.

6. I've seen that concrete mix before, on pre - war or wartime poured slabs esp. air raid shelter roofs.

7. A corded jack hammer, used carefully, will easily nibble the slab - perhaps block off the chamber just below the slab to catch debris.

8. My view is that you shouldn't have mentioned any of this to your utility.
However, if they are anything like the crew up here you wont hear any more from them - just lie low for a while, & then you or your local builder do the work.

9. Your neighbour must be consulted. Perhaps propose a new boundary wall on your side, the drop is unsafe for children or vehicles.
With a suitable crane and some straps, you could just lift that slab off, knock away a couple of courses of bricks, and lower the slab back down onto a bed of mortar. Job done in an afternoon.

That a smart idea and possible solution, it had certainly never occurred to me to lift & shift the slab.

The thing is, the slab surface should finish up well diminished in area - its too wide, for example, stepping into the neighbour's driveway.

Plus, i assume that the OP's idea is to get the slab/manhole level with his drive.
This could introduce a few tricky details - it would really depend on how the OP wants it all to turn out?

There's also the faint possibility that the point loads on the straps might end up splitting the slab with debris crashing down the M/H. Doubtful if there's any re-bar. However, i now wonder if it was originally lifted into position?

I'm a bit of a job's comforter here because we once had straps snapping while lifting a v. large DG frame into an undertakers would you believe it.

Anyhow, if you dont mind me saying so, your proposal is a good'un.

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