Sub base like sponge! - Concern or not?

[mcelec]

hi, i have excavated my front garden ready to lay the mot 1, the garden was origanally part excavated before i moved in and had become water logged so i have excavated this area to around 350mm the problem i have now is there is a couple of small areas which are very spongy, for example when you press the area with your foot the ground will press down 10mm or so and then return to where it was when you remove pressure, there are no signs of water, what i planned to do was dig these soft areas out and fill with mot 1 but a builder who is related to a friend of mine called round and had a look and has said that the pressure of the digger on the ground will of damaged the underlying lead water pipe causing it to leak and therefore making the ground go like a sponge, and so he has offered to replace this pipe for £600.

does his opinion sound spot on or could it be something else? the water pressure in the house is still the same and there is no browning of the water from the tap and no sign of water in the excavated area, i have dug out one of the soft spots and there is solid clay about a further 300mm down and no sign of moisture?

any advise will be very much appreciated as i was hoping to get my mot1 down this week.

[Pablo]

It would be unlikely that the digger has burst the pipe it may have crushed it but unless the bucket nipped it. If you have lead pipes then I wouldn't hesitate to replace them whilst the area was dug up. How large are the soft areas?

[mcelec]

there is about four soft spots each about 500mm radius, they are all in the areas which use to be very heavilly water logged and so i assumed it was as a result of that but then this builder has put doubt in my mind, im planning to dig a trench and run a new plastic water supply in ready to be connected in the future.

could these soft spots be a major cause for concern? or is it that driving the digger over the ground for the last couple of days has forced the moisture out of the ground like a sponge?

[msh paving]

Chances are the digger has made the soft spots worse,might be a idea to put a geotextile "terram" or similar down before the type 1.
if it was a burst pipe water would be flowing out.
£600 is alot off money to replace a lead main considering blue pipe 25mm dia. is around £40/50 for 100m MSH

[Mikey_C]

Do you have a water meter? If so switch off your stopcock in the house and see if the meter is still going round. Your local water board may be able to replace the lead pipe and may do it for free (lead pipe supposedly causes lead poisoning). £600 is "a lot" of money bearing in mind you have done the hard work. Also if you do remove it the lead pipe will be worth a few quid for scrap.

[msh paving]

lead is fetching £200ish a ton you might get 50kg out of it ,for the digging it out it hardly worth the effort,
Most water companys replace lead for free,you need to ask them,i'm doing a lead replacement water service this week I have to do from stop cock to house they do the rest MSH

[mcelec]

so could this sponge type effect on the ground be the water pipe? im inclined to think it isnt because there is no drop in pressure to the house and no signs of water making to the surface and when i dig out the soft spots they dont appear wet or well up with water as you would expect! im hoping that i can dig out these soft spots and refill with mot! has anyone come across this before? or is it just my bad luck? lol

[Dave_L]

As before, are you on a meter mcelec? Shut your stop cock off where the water supply comes into the property - does the dial move??

I too am certain your water company will replace lead service pipework FOC. It's worth a try.

£600 is a whole lot of money seeing as though you've done the lions share of the works! It doesn't sound like any more than a mornings work to complete the replacement from the property to the boundary. That's as far as you'll be able to go, the water board will do the work from the boundary to the water main.

[rimexboy]

Im not so sure they will, when i done my front drive my stop cock was leaking so i called my local water company essex and suffolk water they said they can replace but at a cost of around £400 but i had to have the pipe exposed to a depth of 600mm, so in the end i dug it up and ran a plastic pipe myself, when i dug out to my boundary i dug slightly under the footpath and then joined onto the lead pipe, you can get all the fittings from your local plumbers at not a great cost, also you will have to turn the water of in the road to your house, now im not sure if you are allowed to do that but i took a chance and did and saved myself the diffrence of around £340.

also what made me more determind to do it when i done my drive was the fact that i only wanted my drive up once.

hope that helps
simon

[Rich H]

Some will, some won't. They only have to replace the service pipe (that's the one from the distribution pipe to your boundary).

Soft spots are more often caused by the MOT becoming fluid in already wet ground or by fluid clay in the sub-grade.

To take one look and make a costly diagnosis is bullshit.

[lutonlagerlout]

sounds like BS from your mates mate TBH
my water bloke charges around £250 for most mains and thats using a mole and supplying the pipe and fittings (depending on depth and length of course) its only a days work tops
LLL

[nando]

ro

[Mikey_C]

if the sub grade is has a large clay content it can be bit fluid/sponge/flexible when wet. If it gets a chance to dry out before you put down the MOT it will go a hards a rock. bit like when you fire a clay pot. once you are happy with the water main it may pay to put a geotextile (terram, tdp, ect) down before your MOT

[jay-Manor Driveways]

dig out the soft spot fill with type 1 , lay tarram over the area then type 1 the rest , soft spots are very common

[Dave_L]

Spongy sub base - we've had that - leave it alone - what is today's problem will be fine tommorrow.

We've had sub base moving about like pea soup before - got so wet due to rain we had to abandon site.

Come back in a few days, it was hard as hell (and stable) - thats limestone for you!