bedding inspection chamber

[sm_jamieson]

I have fitted 450mm inspection chamber (had to be changed from 300mm after correspondence with BCO (grrrrr). I know about bedding the drainage runs in pea gravel etc. But what about the chambers themselves ? A couple of related questions.

1. The plastic chamber has a hollow base formed by the underside of the moulding, and little legs around the edge. I've left a good space

8" or so underneath to put concrete to give it a good foundation. It is currently supported where the concrete will be, by bricks. How far do you usually put in the concrete - just supporting the little legs, or right up under the moulding so the whole thing is supported underneath ?

1. How do you backfill around the chamber ? With pea gravel, or with soil. Note that eventually a recess cover filled with paving will be placed on top, and this will need to be supported by a good ring of concrete around the chamber, and I can't see how this concrete can be supported on pea gravel around the chamber.

Thanks, Simon.

[Jim Alexander]

manufacturer's installation instructions eg

will answer your questions.

Jim A

[sm_jamieson]

eg

answer your

Well, the floplast site (screwfix stuff) says very little. I've also looked at marley and hunter. The approaches I have seen are backfilled with granular fill as around the pipes, and the frame and lid supported on concrete which in some diagrams extends enough to ensure the frame/lid is supported on surrounding ground rather than the backfill, sometimes not ! Or, the whole thing incased in concrete, bottom, sides and frame/lid. In no case have I seen what

suggest, which is a solid concrete slab underneath, and text suggesting that this is supporting any weight on the lid transferred via the risers. So I guess a commonsense engineering approach is required. Which probably involves lots of concrete !

What I was really hoping was, how do folks usually do this ? Any comments from experience ?

Simon.

[Jim Alexander]

I don't think the

advice is accurate. I prefer the hunter plastics info. For domestic including domestic driveways I don't think a concrete base or a full depth concrete surround is required, only a

150mm deep concrete support ring is required. Whether the concrete ring bears on the granular sidefill or the surrounding ground does not really matter, both materials are effectively incompressible for domestic loads.

Well as you have found out before backfilling you need to satisfy inspection, mainly gradient and bedding. After backfilling anything goes. I think the specs are clear.

Jim A

[sm_jamieson]

Yep, its the concrete ring on the top bearing the weight. Fair enough ! Although concrete underneath wouldn't hurt, even just to hold the thing in place while you fit the rest of the drainage. I was wondering in what state the BCO would want the drains. I guess partly bedded so he could see how you've done it in all aspects. Also, I'm not sure about testing. My stuff is connected to old clay which disappears into the soil and down 2 metres to the public sewer. Dunno what parts of this could be usefully tested. Simon.

[Rick Hughes]

Bed down on pea gravel, 100mm thick, insert chamber at correct depth, fill all round with pea gravel at least to within 100mm of chamber and the rest with graded back fill. This will suit all domestic installations.