Foundations - Foundations for a wall approx 4ft high

[smiffy]

Hi
I am building a wall approx 4ft High and have come across 2 problems.
I and digging out a trench for foundation and have come across a drainage pipe, This is approx 10cm below the trench depth,can I lay the foundation on top or will the put to much presure on the pipe .

Second problem i have come across a gas pipe that will be just above the foundations am i right in thinking you can by a brick that is arched to resolve this type of problem. ???

[Tony McC]

I'm not sure what you mean about the drainage pipe being 100mm below "trench depth" - do you mean 100mm below the bottom of the trench? If so, the pipe is usually encased in concrete and used to form part of the overall strip footing, but, in some cases, the fotting can 'bridge' the pipe. It all depends on the type of pipe, the thickness of the footing, the presence of any reinforcement, and how much work is involved.

If you can get away with it, bridging is a much simpler option.

Gas pipe - build it into the brickwork or wrap it in a sleeve and build the sleeve into the bwk. Do you know what I mean or is further explanation necessary?

[smiffy]

Tony
Thanks for the reply Great help , I now know what to do with the Gas pipe.

As for the drainage pipe it will be approx 100mm below the foundations. It is not cased in concrete but it runs at an angle to the foundations about a 3rd of the total length, I was only going to do the foundations about 200mm thick as the wall is just below 4ft.

so i am not sure if i put the foundations on top and then build the wall if it will cause problems.

not sure please help.
Smiffy

[Tony McC]

Oh eck - if the drain pipe isn't laid perpendicular to the footing (or nearly so), it's more of a problem, especially if there's a joint involved.

The two 'fixes' most commonly used would be either to "bridge" the pipe with steel beams, which can be expensive to say the least, or to divert the pipework in some way so that it either misses the footing completely, or crosses it at the perpendicular. Is there any way you could divert?

[smiffy]

Tony
Moving the pipe is not an option, for your info its a clay type and for some reason goes across the whole Drive way.

What i can do is alter the Angle of the wall and foundations this would mean i would cover approx 60cm of the pipe going across at an angle. (there are 2 joins in this section) Would that help.

Or If i raised the foundation level and covered the pipe with some type of hardcore would that be ok

Or am i left with bridging with steel pipes if I am any guidance on where i can find info on this.

Once again thanks for your help.

[danensis]

Could you not put a line of concrete blocks vertically alongside the pipe and bridge across the tops with slabs, or haven't you got the depth for that?

[Tony McC]

I think you need a BCO to take a look at this. It's probably not a good idea for me to guess from this end of a computer.

[thomas.mclaughlin@dsl.pip]

Hi gents....i have similar problem although slightly simpler in that my drainage pipe which is plastic and runs at 90deg to the found. However, can you advise how much i should dig below the pipe in order to encase it within the found. Also, what should i use to build some sort of sleeve around the pipe to protect it before pouring the concrete ?

[Tony McC]

Tom - not a good idea to use your email address as a username ona forum such as this. You'll be getting lots of interesting emails in the very near future! Edit your profile and change your username to summat such as TomM or similar.

Anyway, on to your problem: The pipe should have around 150mm of concrete all around and to 'sleeve' it, the simplest trick is to use a length of plastic pipe that has been sliced lengthways. Slip one half underneath the pipe, the other on top and use cable ties or tie-wires to lash them together. If this is a 100mm pipe, use 150mm plastic for the sleeve; if it's 150mm, use 225mm - any gap between sleeve and pipe can be packed with sand or that expanding foam filler stuff.