Cutting into concrete floor - cables and pipes etc

[smith8347]

I wasn't sure which forum to post this under, but my problem is to do with installing underground soil pipes which I guess is a builder's job.

I am installing a new ground floor toilet that is located several metres from the existing foul water drain, and the new toilet will also be in the interior of the building away from any walls. I am going to need to cut a long trench (4 or 5 meters) through the concrete slab for the soil pipe. I am planning to use a wet saw for this task cutting through the entire thickness of the slab (200 mm). Then break apart the strip, lift out the chunks of concrete and dig by hand through the underlying ground to the required depth.

I am wondering how to avoid cutting into pipes and cables when using the saw? I know for a fact that the slab is full of central heating pipes, but these aren't my main concern. My main worries are hitting the water mains or electrical supply.

Due to the position of the stopcock in relation to the front of the house, it is quite likely that the line of the new trench will cut across where the water mains comes in from the street, but is it safe to assume that it will be buried too deeply to need worry about hitting it with the saw?

It is less likely that the electrical supply will be in the way, but for obvious reasons this is the most worrying possibility if the saw was to come into contact with it..

What kit would I need to purchase/hire to trace out the location of these services with reasonable accuracy?

 

[tell80]

No need for a wet saw or to do a 200mm deep cut in one go - you can use a 7-1/4" circular saw with a masonry blade.
Mark your lines and simply nick the concrete about 25mm-35mm deep in 10mm or so increments.
Chisel out what you've cut, and repeat - only this time chisel out every 300mm as you cut.
Make sure all utilities are isolated.
Once you are at about 65mm deep then work along the cut "trench" with a lump hammer simply nibbling & breaking through the remaining depth of concrete.
This way you should see any conduits or pipes in advance.

 

[Hugh Jaleak]

Water Service should be around 750mm deep, so well below slab level. Make sure the external stopcock in the road works, just in case!
Electricity might be easier to locate, hire a CAT (Cable Avoiding Tool) and scan the route of your proposed trench, it should indicate the presence of any cables below.

What do you propose to do with the CH pipes?

 

[smith8347]

No need for a wet saw or to do a 200mm deep cut in one go - you can use a 7-1/4" circular saw with a masonry blade.
Mark your lines and simply nick the concrete about 25mm-35mm deep in 10mm or so increments.
Chisel out what you've cut, and repeat - only this time chisel out every 300mm as you cut.
Make sure all utilities are isolated.
Once you are at about 65mm deep then work along the cut "trench" with a lump hammer simply nibbling & breaking through the remaining depth of concrete.
This way you should see any conduits or pipes in advance.

That sounds incredibly time and labour intensive, and only slightly reduces the possibility of damaging a pipe or cable accidentally. Am I missing something?

 

[smith8347]

Water Service should be around 750mm deep, so well below slab level. Make sure the external stopcock in the road works, just in case!
Electricity might be easier to locate, hire a CAT (Cable Avoiding Tool) and scan the route of your proposed trench, it should indicate the presence of any cables below.

What do you propose to do with the CH pipes?

OK, reassuring to know that the water should be safely buried. To be honest I was concerned because while carrying out some other work I ran into a 22 mm copper pipe of some sort, this was only about 100 mm deep and set in the concrete. I think it may have been the (disconnected) gas supply so it had me thinking that the water might also be at a similar depth.

I will look into cable avoiding tools.

With the CH pipes I can sort of figure out where they are likely to be from the position of the radiators, and if I cut through them either repair or isolate the pipe. Some of the radiators are getting removed or relocated and I will probably run new supply/return via the ceiling.

 

[Hugh Jaleak]

Just bear in mind the Water Supply should be that sort of depth, but usual practice is for it to turn and come straight up into the house at the point of entry into the building. Gas could well be a lot shallower, if in any doubt of the location of any service, identify where its likely to be running before digging, and then dig carefully until the location is proved.