"sm_jamieson" wrote in message
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On 27 Apr, 08:18, "Jim Alexander" wrote:
"sm_jamieson" wrote in message

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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 ?

2. 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.

manufacturer's installation instructions
eghttp://pdf.hunterplastics.co.uk/pdf/underground/ugt7.pdfwill answer
your
questions.

Jim A

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 http://www.pavingexpert.com suggest, which
is a solid concrete slab underneath, and text suggesting that this is
supporting any weight on the lid transferred via the risers.

I don't think the www.pavingexpert.com 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.

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

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