Land drainage - Materials

[GazzaC54]

I have just had installed a land drainage network but having read the webpage on this website I am now very concerned about the problems I think might happen. My garden has a natural fall of over 1m from the house to the bottom of garden. It has a ditch on one side (right) that is 1.5m lower than the lowest point which is on the opposite side. The soil is heavy clay. The landscape gardener has dug a trench from the lowest point (32.26) to the ditch floor (31.04) and laid in 21m of plastic land drainage pipe 160mm diam., on top of bed of 40/60m stone. This runs across the bottom of the garden. He did not compact the stone before laying the pipe on top. He then laid on top of that more 40/60m stone and laid on top a strip of weed surpressing fabric and back filled without compaction with the clay he dug out.
This pipe is to take all the surface water from house and garden (1 acre) into the ditch.
He then dug out 4 trenches at right angles to this pipe and laid in 100mm pipe. He did not use any connectors to join the 100mm to the 160mm. He did the same as he did for the 160mm using the same material etc.,
He has also dug a trench and laid in Osmo pipe for the surface water from the house and conservatory which he has run to the end of the 160mm pipe and again has not used any connectors. He has also not used any end caps on any of the pipes.
He has also dug herring bone trenches for more 100mm pipe which in places is less than 1 ft from the surface and again no connectors used.
To cap it all whilst digging trenches for water and power he cut through the land drainage pipes he installed and fixed using OSMO and mastic. He has also driven cement lorry, dumper trucks and diggers over the whole area so I can now see by the drop in soil level where the ditches are. I intend to grow trees and shrubs in areas that have piping and I am very concerned that the right materials have not been used, no compaction has been done and no Geo textile envelops the stones in the trenchs, no concrete apron has been built at the outfall and it looks like the size of the stone used will cause sinkages in the level of the land. Am I right to be concerned ?

[seanandruby]

The size of stone us not a problem. He should of started his dig from the outfall and allowed 1/100 200 ish fall with reasonable depth below the pipe for a concrete run off. He should of built an header wall, quite easy out of sand bags. Should of used joiners for pipes and end caps .the trench should of been lined and enough surplus to cover over the top layer of stone. Perf' pipes should be wrapped in terran. Tracked plant would be a better option for driving over shallower trenches. Solid pipe is ok for the house drainage.

[GB_Groundworks]

we always use connectors but never cut the main run for laterals, always cut the the multi joint in half then cable tie back together with a 100mm hole cut in the main run, we wrap all our land drains in geotextile now, candy pre wrapped or buy 100mm rolls of geotetile socks or just cut up needle punched non woven geotextile and wrap round the pipe. clean drainage stone will not compact as there is no fines.

compacting the clay would be counter productive to drainage, we will to within 100mm of the surface, lay geotextile and fill with a sandy soil mix and turf

you'll likely have far too much compaction on your grass/land now if all thats been run over it

it'll need hollow tining or vert drain to break up some of the compaction

we tend to build drystone wall headwalls as there are more in suiting with where we work, the last 1m of the pipe to headwall should be smooth not flexible perforated pipe.

but if no headwall into the ditch big chance of it being eroded

standard practice is to lay the pipe on the trench bed, my mate runs a sportsfield firm they do 30-50km of drains a summer always pipe on the trench floor then surrounded with clean granular fill

[seanandruby]

My Webpage
As stated the contactor used 100ml perf" pipe, so cutting a 200ml hole isn't possible. The link above shows the connectors you need. As Giles stated the fill material ( clay) will be useless at draining now it had been sealed by the heavy plant. When i said sand bags i meant concrete filled ones.

[GazzaC54]

Thank you all for taking the time to reply, they are very useful.
I have some photos of the work being done and more recently after I have hand dug some investigation holes and I am horrified that this so called professional groundsman has done so many things wrong. If I knew how to post images I would share them to show how not to lay land drainage. I now can not wait for my meeting with the landscaper and landscape designer to show all the crushed pipe, slippage of soil into stones and foul smelling water that is not soaking away.

[seanandruby]

Go to noticeboard at top of main page and there is a post on how to upload photo's.

[GB_Groundworks]

My Webpage
As stated the contactor used 100ml perf" pipe, so cutting a 200ml hole isn't possible. The link above shows the connectors you need. As Giles stated the fill material ( clay) will be useless at draining now it had been sealed by the heavy plant. When i said sand bags i meant concrete filled ones.

They laid 160mm main drain with 100mm laterals