Winter poser for 10 - Ground pressure and drains

[Tim W]

I've just humped a ton of coal from it's delivery pallet to a couple of old

1m crates round by the shed.

While my bath is running, I was thinking...

Approx 1m under the ground under the coal is a 9" salt glazed drain. The coal exerts a ground pressure of 1/2 tonne/m2 (2 crates) over about 2m2 directly over the top.

Whilst I don't doubt that something 1m down is barely going to be aware of that, the poser for 10 is:

How much ground pressure can you safely apply on top of (presumably) unprotected saltglaze drain pipes? Is there a table somewhere of numbers like that?

eg (relevant to me)

1) Could you drive a 1-2 ton digger safely over the top?

2) How much extra soil could you bank on top if you were messing with ground levels?

3) Is it a bad idea to leave that sort of load (eg my 1 tonne of coal) on top forever? This is more relevant to if, I made a sand and ballast bunker with upto a ton of each and plopped it over the drain (they are sitting in the front garden and will get relocated when I have a digger down the line).

Drain runs near the fence in a mouldy bit of the garden so it is a rather obvious location for crap.

OK - I realise the obvious point of: if the drains had a problem, you'd have to remove the crap on top to dig down, but ignoring that for the sake of argument...

Just curious...

Cheers

Tim

[robgraham]

Tim - I'm can't answer your question I'm afraid, but do ask for your sympathy with respect to salt coated drains!

I have a long branch from the back of the house - just the main bathroom, which runs down the road side of the house to the septic tank at the bottom of the garden. More than adequate fall. It has obviously over the years deteriorated most likely due to cars being parked near it's line. There had to be repairs 18 months ago and then another major blockage 5 months ago.

Today - a serious blockage. At least strictly last night when I went for spuds from the cycle shed to find that *it* was the overflow from yet another blockage. This time, I discovered this morning, the block was below the join of the front and back pipes, so just everything backed up into the cycle shed!! Not nice to say the least, and I had to get the professionals ....... in hurts the DIY pride that does, let alone the pocket.

The only brightness is that the insurance company are making the right noises about re-laying the drain for me.

Rob

[Andrew Gabriel]

Parents had a problem about 3 years ago. Camera showed lots of tree roots coming in at the pipe joins, and that meant it was covered by insurance. They don't cover wear and tear, but do cover tree damage. A firm came out, cut the roots off, and relined the sewer, and that section has been OK since.

[newshound]

ISTR that civil engineers assume that forces spread out through average soil at an angle of about 45 degrees. So say you were loading a 1 metre diameter circle; by the time you are 1 metre down the load is spread over about a 3 metre diameter circle. So I don't think I would worry about the sort of distributed load you are describing with salt glazed pipes a metre down. It might be different if you were driving HGVs or JCBs backwards and forwards over them for a long period.

[Tim W]

newshound wibbled on Saturday 05 December 2009 21:15

Ah right... Thanks for that :)

So 1x2m load area, leads to a load area 1m down of about 11m2 (4m long by 3m wide with rounded corners), so about one fat bloke per m2. When you reckon it like that, it sounds less ;->

Things always seem better when you can appreciate the fundamentals.

Cheers

Tim

[Chris Hogg]

A 40-yr old book on ceramics that I have says roughly the following : Crushing strength is related to internal diameter, wall thickness and wall porosity. The crushing strength for most _concrete_ pipe should be a minimum of 1350 lb/ft of length, and salt glazed pipe is usually higher.

Googling for "crushing strength" "salt glazed" pipes gives

both of which say their pipes have a crushing strength of 16kN/m length, which if my maths is correct, is about 1100 lb/ft length, but these are not UK.

[Tim W]

Chris Hogg wibbled on Monday 07 December 2009 19:21

Thanks for that Chris. That's over 1.8 tonne/m length (I presume over the width of the pipe). That translates to a pretty massive ground pressure then.

I suppose the greater risk is actually moving the ground and cracking the joints?...

[Chris Hogg]

Pipe manufacturers used to use the same test as for concrete pipes, BSS556, 1955 apparently. The ASTM test, 301-54, is similar. I imagine there are more-up-to-date versions now. The test says that the pipe should be placed longitudinally between bearers of 6 in. width with rubber packing, which shall extend the full length of the barrel of the pipe. So something like this I guess (if my ascii art works!):

| | | | steel | | ram upper | | ---------------------- ------- ////////rubber//////// //6in// ---------------------- length of pipe O ---------------------- ////////rubber//////// //6in// ---------------------- ------- steel | | ram lower | | | | | |

(except that the diameter of the pipe is much larger than I can show).

IYSWIM

IANAE, but that would seem reasonable.