Clive wrote:
Hello,

I have two problems related to a sewer manhole.

The first is relatively easy. The manhole cover is cast iron, really
heavy, has lost its little lifting bars / rods that used to lie on top
of semi-circular "recesses". The manhole cover has cracked and is
really, really difficult to lift using an old screwdriver that keeps
on slipping out from the "lip" of the cover. For all these reasons I
want to replace the cover. The cover is in a small, paved front
garden and nothing heavier than a full dustbin passes over it. Can I
replace the cast iron cover with a galvanised steel one?


You can use plastic if you can get one to fit, although galvanised is
cheaper.

The second problem is related to the first. All of the front garden
is paved with some incredibly horrible slabs. I remember when a couple
of slabs were lifted years ago that they are laid on tarmac - don't
ask me why. The slabs have been down for at least 30 years. The
problem is the slabs around the manhole have "heaved". Think of the
edges of the slabs next to the manhole have all been "lifted" so that
water on them would run away from the sewer manhole. Now the slabs
are not moving at all when you stand on them, they feel completely
secure. I lifted the manhole cover (with difficulty, see above). I
inspected the brick lining of the "sewer access". There the bricks
seem all intact and that nothing seems to have moved. However, the
bricks just below the manhole cover "frame" are of a different type
to those lining the "sewer access pit". The mortar is very rough and
bits of slate acting as "shims" are in there too. I am guessing that
when the paving slabs were laid the whole level of the front garden
was lifted so the manhole cover frame had to be lifted too and it was
just bodged up when it was relaid. Now .... I can't see any reason
from inspecting the lining of the "sewer pit" why this "heave" is
happening. Hence, when I replace the manhole cover and the slabs what
is the possibility this "heave" will happen again?

It's highly likely that the area around the manhole has been dug out to a
decent depth (to relay the upper courses of brick) and filled in with
hardcore or even concrete....when the rest of the garden has settled, this
part has not.