Clay Field Drain
Steve J
discovered an old field drain running across the site. It passes through
the line of the new walls and directly under where the new Inspection
Chamber for the foul water drains will be. The drain is constructed of 1
foot 'U' shaped sections of 4" clay pipe laid end to end to form a channel,
another set of sections is laid ontop to form a pipe.
What should I do with this drain?? - remove it, leave it (its pretty badly
damaged), replace the part that passes through the foundations and under
the manhole with UPVC? - the soil is clay and I don't want to cause it to
become water logged.
Any advice or experience greatly received.
--
Regards
Steve J
Alistair McDonald
st...@REMOVETHIS.stagebase.demon.co.uk says...
>
> What should I do with this drain?? - remove it, leave it (its pretty badly
> damaged), replace the part that passes through the foundations and under
> the manhole with UPVC? - the soil is clay and I don't want to cause it to
> become water logged.
>
> Any advice or experience greatly received.
>
I have no experience, but I certainly wouldn't build ANY structure over
either the existing drain or a replacement. Personally, I'd block both
ends WELL clear of the proposed building, and take out the piece in the
middle. If you've got raft foundations, I'd fill the trench very
thoroughly, but if you've got strip foundations you'll be OK I imagine.
You *might* want to re-route away from the building; if not, I'd make
sure I can at least get access to the stopped ends of the drain, should
the drain prove to be "live" and need to be reconnected after a
particularly rainy period [1].
I'm sure that others have more experience and will add sage advice.
[1] Well, I know that this time of year is the "particularly rainy
period."
--
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| Check my address for Anti-Spam measures.
cormaic
allym_...@usa.net(Alistair McDonald) enriched all our lives with
these words:
8<---S-N-I-P--->8
>You *might* want to re-route away from the building; if not, I'd make
>sure I can at least get access to the stopped ends of the drain, should
>the drain prove to be "live" and need to be reconnected after a
>particularly rainy period [1].
It should be assumed that any field or land drain is 'live',
as they are reliant on surface gullies or foul water disposal for
their often seasonal flow. It's best to cut out the section of clay
land tiles that are obstructing the construction work, and use
flexible plastic land pipe to reconnect the severed ends via a
diversion that lies outside the area of construction. Provided that
the new pipe is laid more or less to the existing grade, even if there
are flattish spots, hydrostatic pressure will ensure the flow.
If we were undertaking this sort of work, we would suggest
that a small access chamber be incorporated at a convenient point
along the new line, which will allow rods or other drain equipment to
be inserted into the new line if a problem develops.
There are more detials of land drainage on my web pages.
--
cormaic - paving pages at http://www.tmac.clara.net/paving2.htm
Culcheth - Last Updated on February 1st 1999
cormaic CAN BE FOUND AT tmac DOT clara DOT co DOT uk
Steve J
The Drain runs under the existing structure of my house anyway, so I can't
re-route it away from the construction completely. I am building a new
kitchen on the back of the house, so the drain will pass under the back
wall of the house (as it does now) at about 45 degrees to the wall, it then
continues under the proposed kitchen floor and passes through the line of
the new foundations of the side of the kitchen. The strip foundations are
proposed to be 1200mm deep, the drain is at about 800mm so I guess it must
be treated in the same way as the other pipes that are passing through the
foundations. The drain runs away from the house across the garden and
under the boundary into next door's garden about 7m away from the line of
the back of the terraces.
I am worried about replacing the drain under the floor and foundations with
perforated pipe in case it allows water to escape into the clay surrounding
the foundations (the original kitchen suffered subsidence due to water
logged clay), how about if I replace the pipe under the new building with a
waste pipe and then replace the part that runs across the garden with a
land drain as detailed on your web page ??
--
Regards
Steve J
cormaic <cor...@NOSPAMTODAYTHANKStmac.clara.net> wrote in article
<36f5385c....@news.clara.net>...
John Schmitt
"Steve J" <st...@REMOVETHIS.stagebase.demon.co.uk> writes:
>Whilst digging the beginnings of the foundations for my new kitchen, I have
>discovered an old field drain running across the site.
Not the best of news, I hope you have deep pockets.
>What should I do with this drain?? - remove it, leave it (its pretty badly
>damaged), replace the part that passes through the foundations and under
>the manhole with UPVC? - the soil is clay and I don't want to cause it to
>become water logged.
In the UK, virtually all the clay is saturated with water, i.e. all the voids
are occupied by water, so the clay is already "waterlogged". What the problem
is, is that the majority of the clays in the UK are overconsolidated, i.e. they
have in the past been under much greater pressure. This means that they are (to
use a gross oversimplification) like a coiled spring and if they get acces to
water they will swell. Conversely, if (e.g.) a tree extracts water from the
clay it will shrink. Either of these two situations will cause differential
movement, which may compromise the structural integrity of a building. To
further complicate things, the building exerts a stress upon the clay, and
settlement occurs. However, in most cases this settlement is mostly uniform, so
it is not regarded as a problem. Surveyors rarely have a proper understanding
of soil mechanics, and one can have endless fun asking them questions about
whether the geological term "compaction" is equivalent to the soil mechanist's
"consolidation", and why.
The overconsolidation is due to the last ice age, when several tens of metres
of ice overlaid England down to about the southern edge of the M25.
One day I will write a settlement FAQ. One day.
John Schmitt
But still, Wittgensteinians dress like slobs, and it was a pleasure to see so
many well-dressed philosophers in one place. - D.M. Procida
Disclaimers apply.
Andrew Heggie
wrote:
>
>In the UK, virtually all the clay is saturated with water, i.e. all the voids
>are occupied by water, so the clay is already "waterlogged". What the problem
>is, is that the majority of the clays in the UK are overconsolidated, i.e. they
>have in the past been under much greater pressure. This means that they are (to
>use a gross oversimplification) like a coiled spring and if they get acces to
>water they will swell. Conversely, if (e.g.) a tree extracts water from the
Do you mean that even with centuries of rain on the surface the
underlying clay has never reabsorbed its full "quota" of water.
If so is this why a wheel rut cannot easily be made good? I am just
interested as I would like to reinstate some tracks without recourse
to importing stone/rubble.
AJH
cormaic
<st...@REMOVETHIS.stagebase.demon.co.uk> enriched all our lives with
these words:
8<---S-N-I-P--->8
>I am worried about replacing the drain under the floor and foundations with
>perforated pipe in case it allows water to escape into the clay surrounding
>the foundations (the original kitchen suffered subsidence due to water
>logged clay), how about if I replace the pipe under the new building with a
>waste pipe and then replace the part that runs across the garden with a
>land drain as detailed on your web page ??
I've never come across a land drain passing beneath an
existing property, and so, the following might not be absolutely
correct, but you could easily check it with your local authority
building control (LABC).
It's not a good idea to have a perforated pipe laid beneath an
extension, particularly one of the flexible-corrugated types, or any
other plastic, as they are not as resistant to deformation as rigid
types, such as clayware, and would therefore need to be encased in
concrete before building over to provide the required strength. This
encasing in concrete also stop them acting as a land drain, and so
defaets the point of using them.
I would cut off the existing line as near as possible to the
existing building, and replace with a vitrified clay (vc) type,
connected via an adaptor collar. You LABC will have a standard spec
for this type of pipe passing beneath a structure, which will probably
require concrete encasement of the new vc pipe to 300-600mm outside
the building, at which point you can use another adaptor collar to
reconnect to existing, although I would still recommend an access
chamber at this point.
Wall Wall O U T S I D E
|| ||
H O U S E || E X T E N S I O N || access chamber
|| || | |
ex drain || new vc pipe || | | ex.
==================||++++++++++++++++++++++||++++|_____|========>
Cross-sectional plan.
I hope this makes it clearer; if not, you can email me and
I'll send you a proper drawing. :~)
John Schmitt
(Andrew Heggie) writes:
[on clay]
>Do you mean that even with centuries of rain on the surface the
>underlying clay has never reabsorbed its full "quota" of water.
Yes. The clay is very impermeable, and for the most part, after the first metre
down, has not had access to water to swell. the rain tends to leave sideways as
runoff, as opposed to downwards. In London the clay from 10 metres down is very
dark in colour due to the fact that it is so firmly consolidated, but on access
to free water, changing colour to match the clat at the surface. It is also
very hard, almost like wood.
>If so is this why a wheel rut cannot easily be made good? I am just
>interested as I would like to reinstate some tracks without recourse
>to importing stone/rubble.
One of the reasons, yes. Clay resists dynamic compaction very well because of
it's low permeability, and when the clay has been extruded to form the ruts,
it's moisture content will be far above the MC for optimum compaction. You
could use geogrid, and a capping of gravel or crushed stone to make a quite
reasonable roadway. On clay sites, it is quite common for contractors to do
just this as a temporary roadway, as the cost of doing this is cheap compared
to the consequences of a bogged lorry.
Steve J
with the very helpful building inspector at my LA and see what he thinks -
I'll let you know the outcome.
--
Regards
Steve J
cormaic <cor...@NOSPAMTODAYTHANKStmac.clara.net> wrote in article
<36df8586...@news.clara.net>...
Steve J
at least 120 years old) actually serving any purpose - its about 800mm down
as it emerges from under the house??
--
Regards
Steve J
John Schmitt <joh...@alpha1.mdx.ac.uk> wrote in article
<7bm39k$c03$1...@aquila.mdx.ac.uk>...
Richard Gethin
<st...@REMOVETHIS.stagebase.demon.co.uk> writes
>If the clay is impermeable, is this old drain (it predates my house so is
>at least 120 years old) actually serving any purpose - its about 800mm down
>as it emerges from under the house??
Can you see where it comes out the other side of the building?
--
Richard Gethin
Steve J
Because it is at an angle to my house, it must pass under the party wall to
next door at some point around where the stairs are in the middle of the
house. It must then run under the living room of my neighbors house - I
dont think this room will have ever been a wet room in the past. Given the
angle it runs at (assuming it runs in a straight line) it should emerge
from the front of the terrace at some point round about the boundary
between my neighbor and the house beyond that. I've had a good scout
around for manholes etc in the front gardens concerned - nothing obvious.
The drain is running away from the from of the houses so I guess it isn't
connected to the sewer in the street!
It remains a mystery, this is why I assume its field drain that pre-dates
all the houses in the street.
--
Regards
Steve J
Richard Gethin <ric...@rgethin.demon.co.uk> wrote in article
<4b5wULAL...@rgethin.demon.co.uk>...
John Schmitt
"Steve J" <st...@REMOVETHIS.stagebase.demon.co.uk> writes:
>If the clay is impermeable, is this old drain (it predates my house so is
>at least 120 years old) actually serving any purpose - its about 800mm down
>as it emerges from under the house??
Possibly. If you remove it, you run the risk of compromising someone else's
property.