Course - Inspection chamber repair

[davidm]

Hello. I am landscaping my rear garden, and have removed the ugly concrete area surrounding a manhole/inspection chamber. It seems that the metal frame has corroded, and the upper course of bricks are in poor condition and not really bonded together. I can get a replacement (rectangular) cover easily enough, but my question really concerns the height - ideally I'd like to reduce the height by a couple of inches or so because the concrete area was higher than the rest of the garden. Would I be causing a problem or falling foul of a regulation if I do this by removing the dilapidated top course of blues, thereby slightly reducing the height above the drain itself ?

Thanks in advance.

[GB_Groundworks]

no and no

doesnt really matter on an inspection chamber, make sure you bed the frame with a good fillet of strong mortar

[Tony McC]

You can set the height of the cover and frame to any level at all, to suit the ground/garden/paving.

As Giles has said, make sure any new regulating brickwork is properly constructed and you'll be fine.

[davidm]

Many thanks both of you for your prompt replies. I've even learnt a new term - regulating brickwork! I notice that on many pictures of manholes that there is a 'double skin'. As there is only one on mine, I think I'll construct another skin around the two top courses to make a better job.
Great site - thanks again.

[lutonlagerlout]

david the main thing with manholes or inspection chambers is that you use either engineering bricks and LBC commons

dont be tempted to use any old brick

also 100mm walls are ok up to about 450 mm underground

LLL

[Tony McC]

Double skin or 225mm brickwork is standard practice for regulating bwk taking vehicular traffic.

[lutonlagerlout]

sorry,yes I agree
but an awful lot of drives have shallow chambers in 100mm brickwork that is existing
LLL

[davidm]

Another conundrum now...I now notice that the opening is 750 x 550mm, narrowing to approx 460 x 630mm at the top for the standard 600 x 400 steel cover. the narrowing is achieved by means of the bricks of the uppermost three courses 'overhanging' in stages. This seems unsatisfactory to me - surely not a strong solution. and of course, if I'm reducing the height, this will mean a greater overhang! I've though about this and I could either: 1. keep the design as it is but use a larger (600 x 600) cover so that at least two edges are supported well, or 2. build up straight in engineering bricks and then use concrete lintels to support the frame over the larger opening.
Any thoughts?
Thanks again

[lutonlagerlout]

its called corballing and it is a well used technique
you can reduce with precast 100 by 65mm concrete prestressed lintels
LLL

[davidm]

Thanks again LLL. I've just looked at the corballing explanation and pic on the regulating page. Excellent. I'll build it up as explained, keeping an eye on the maximum oversail. It'll be good experience.

[Tony McC]

<pedant mode> It's corbElling, with an 'e' - and as long as you don't oversail by too much on each course, it's highly effective.