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    • CommentAuthorgoodevans
    • CommentTimeJul 12th 2017 edited
     
    Hi all,

    I've hit a snag with planning/tree officer - our access drive (50m long) has a large tree next to the drive which requires protection. The top soil will be left in place with a cellular confinement system laid on top with a permeable top surface (gravel or block paving) protecting the roots from compression by HGV's and allowing water and oxygen to the roots. This has been accepted by the tree officer.

    All our services will need to go down the access drive (gravity is in our favour for foul drainage approx 1:16 fall). Our Arboreal expert suggested that we would be able to lay services in the normal manner - if the trench was hand dug - reserving any roots more than 20mm in diameter - unfortunately the tree officer requires a less invasive procedure - by which I presume means moling or horizontal drilling.

    The root protection area has a length of 26m in one continuous strip - after that I have a strip of around 2m wide and 24m long that does not need any special measures.

    I would like to use the mains drainage (soak-away solutions for anything else is not an option for various reasons).

    I wanted to get service ducts/pipes in place first so that the confined cell system could be laid with a sacrificial wearing course - so that when the later services (gas, electric, telephone) are delivered they could be drawn up ducts.

    As two dwellings are being built I will need 1No 110mm foul sewer, 2 No water mdpe pipes 32mm OD, 2 number 60mm id gas ducts, 2 number telecom ducts (presumably 32mm or so), two number electrical ducts 32mm (37 od).

    The water has to be 350mm away from the gas so I think 6 borings will be best - 2 water, 2 gas, 1 sewer, 1 for the small stuff (electricity & telecoms)

    presumably bedding the sewer in gravel does not apply here and 100/110mm pipe 26m+ long can be drawn into the hole, gas warning tape will have to be laid immediately under the confined cell system etc

    would two pit's 26m apart and 2m wide be able to take all these borings by moling or is directional drilling going to be required, would I need an intermediate pit

    Before I talk to all the different people that I need to I would like a plan+options that sounds about right. would the gas/electricity/water people prefer or allow one pipe serving two meters at the house end of the drive for example

    Any thoughts? - any anyone had to do anything similar (particularly moling pipes suitable for foul).
    • CommentAuthorCWatters
    • CommentTimeJul 12th 2017
     
    How far can you mole in one go? This web site mentions 20m but perhaps that's just the limit on their kit?

    http://www.maxiflow.co.uk/services/drainage/moling-trenchless-pipe-laying/

    Perhaps find out how much the diameter affects cost. If you can mole a 110mm pipe then it might be possible to do it with 4 holes all 110mm..

    1 for sewer

    1 for two the 32mm water pipes and the telecoms

    1 for 2 gas pipes

    1 for 2 electric cables
    • CommentAuthorCWatters
    • CommentTimeJul 12th 2017 edited
     
    The water co may not like one shared sewer pipe because they are required to maintain shared pipes now. But wouldn't hurt to ask them.

    Another web site mentions a 20m limit between pits..

    http://www.eps-trenchlessinstallations.co.uk/moling.php

    "Pipe sizes range from 25mm to 150mm with distances up to 20m installed in one shot (absolute perfect ground conditions)"
    •  
      CommentAuthordjh
    • CommentTimeJul 12th 2017 edited
     
    Posted By: goodevansAll our services will need to go down the access drive (gravity is in our favour for foul drainage approx 1:16 fall). Our Arboreal expert suggested that we would be able to lay services in the normal manner - if the trench was hand dug - reserving any roots more than 20mm in diameter - unfortunately the tree officer requires a less invasive procedure - by which I presume means moling or horizontal drilling.

    That sounds like a very important tree? Maybe it doesn't mean moling the entire distance, perhaps he would allow hand digging a hole at the half-way point or something similar?

    edit: have you asked your arboreal expert why the tree officer has comeup with more onerous constraints than he thought were reasonable?

    Before I talk to all the different people that I need to I would like a plan+options that sounds about right. would the gas/electricity/water people prefer or allow one pipe serving two meters at the house end of the drive for example

    While I understand the urge to get your ducks in a row, this might be a case where asking a local expert - drilling company, or surveyor or planning consultant perhaps - might suggest better alternatives.

    IIRC, the water utility want meters at the property boundaries; the gas utility wants pipes at right angle to mains etc; the electricity utility pricing structure incentivises connections of less than 40 m; and Openreach were fairly flexible. But maybe your results will be different. I think it's a case where an initial chat with the individuals responsible for each service in your case will pay dividends (i.e. the individuals who will come out and survey your particular site for their installation). Early involvement is better than late, IMHO. The utility staff can probably also help you with the question of what the tree officer will accept.
  1.  
    Your site sounds very similar to ours (though we have just one house and two trees and want to route in between them). In the end we've tried to route everything elsewhere instead to avoid the complications and cost of moling but recent events mean we may need to revisit this option.

    We still need to put down the tree protection matting etc. for HGV site access - be aware how much just this aspect costs as we had the wrong gravel quoted and the uplift was several thousand to get the right 'clean stone' in such a large quantity. To get depth for heavy construction lorries, this is around 250mm depth which is a fair deal of extra height to allow for on your access road.

    Our water company have consented to the combined foul and rainwater sewer on the basis that we demonstrated we have no room for soakaway and the land already had a small amount of roofed building and hardstanding so we're just increasing runoff.

    This was accepted on the condition that we limit the rainwater flow to 1l/s so we are installing attenuation crates to regulate this. Quotes are still out on this measure, but our engineer advised us to allow £13.5k for this! Needless to say we're trying to get the costs down. You should allow for some attenuation though if you hope to connect both into the same run.
    • CommentAuthorgoodevans
    • CommentTimeJul 13th 2017 edited
     
    I have access to a ditch which runs into a 10m2 pond with about 2m headroom before overflow (it has never overflowed) and peculates into the ground - so I think surface water is ok (I will be able to attenuate via storage in the no fines gravel and discharge via an oriface to limit flow) - But I won't have a package sewer discharging into this ditch - its too close to us and my neighbours.

    So foul will have to go down the hill via pipe to the manhole on the edge of the road meaning 3 houses in total will share a sewer into the main sewer in the road and 2 houses will share a sewer in the access drive- as far as I can ascertain the water company will adopt the shared sewer if built to standard and BC sign it off - but I will have to apply.

    I think I have a source for the no fines angular gravel - it will have to come from afar in 20 tonne lorries to a local aggregates firm then transported in smaller loads - possibly 4 tonne at a time for filling in the cellular matting. It could cost me about £50/tonne in all + cells at £16/m2 + textile - but I'll use the voids in the aggregate to offset the cost in storm crates and excavation. I'm considering sending the downpipes into this zone as well to avoid having any surface water drains.

    So far as getting the Arboreal consultant going to go head to head with the tree officer - it may work - or it may not - for the moment I'll see what costs I'm looking at. As it's not my tree I am a little risk adverse to damaging it.

    So far the consensus is that I will have to allow at least one intermediate pit in the middle of the root protection area if moling but this is still 'less intrusive' than a trench so I hope a proposal to this affect should satisfy the tree officer.

    The tree is an old elm tree in decline - but still expected to live for at least 20 more years. It has a stem (trunk to you and me) of over 1m diameter hence the large root protection area.

    But the burning question is: has anyone actually moled a 110 pipe through clay?
    •  
      CommentAuthordjh
    • CommentTimeJul 13th 2017
     
    Posted By: goodevansI think I have a source for the no fines angular gravel - it will have to come from afar in 20 tonne lorries to a local aggregates firm then transported in smaller loads - possibly 4 tonne at a time for filling in the cellular matting.

    Why does it need trans-shipping? I thought the point of the road reinforcement was to allow 20 tonne lorries up the road? The load carrying capacity depends on the subbase, not the gravel surface. But in any case the gravel can be dumped at the roadside and spread by a digger & dumper.

    Actually, rereading your first post, it sounds like you're expecting clay topsoil with gravel in a honeycomb to withstand HGV traffic. I don't think it stands a cat in h*ll's chance. I think the clay will rut and the honeycomb will be torn apart. I think you'll need a proper subbase first using DtP type 3 if you want it to be permeable.

    Some moling firms advertise placing up to 180 mm ducts so I'd suggest contacting some firms that provide service in your area.
    • CommentAuthorCWatters
    • CommentTimeJul 13th 2017
     
    "But the burning question is: has anyone actually moled a 110 pipe through clay? "

    Not me but I think clay is no problem.

    http://tpssprod.blob.core.windows.net/sys-master-tpssprodcontainer/hfb/hc6/8800028655646

    Moles
    At Keyline Utilities, we offer one of the largest Impact Mole fleets in the UK. Specifically designed for use in pipe and cable installation without the need for excavation, the Moles are capable of burrowing a hole through any soil type.

    The range includes the following sizes:
    45mm 55mm
    65mm 75mm
    95mm 110mm
    130mm 145mm
    180mm
    • CommentAuthorgoodevans
    • CommentTimeJul 13th 2017 edited
     
    The difficulty I will have at first is to prevent blocking access to the existing house - a 4 tonne pile can be dumped at the bottom of the access drive and can be shifted into the cells (200mm deep) by hand if necessary - in this way I will not inconvenience the household at the bottom of the access drive. As I move up the drive I will be able to take larger deliveries. The access drive is already fairly stable / compacted as it has had light vehicles using it for several years.

    So far as suitability is concerned - the tree officer says yes - that will have to be good enough for me for the moment. anything else and I will have to prove that the system will protect the roots from compaction and oxygen starvation.

    DJH - below is one example of the cellular confinement system for information - it may not be what you are imagining. I will be going for a 200mm deep cell with 100mm of sacrificial wearing course on top - to be replaced with permeable blocks (& bedding layer) at the end of the job.

    http://www.terram.com/request-file.php?fid=116

    But back to moling/drilling - yes I have seen the 180mm moles - but still hoping to hear from anyone who has had experience of 110mm pipe laid by moling - let alone 4 or more pipes. I have a company contacting me tomorrow (hopefully) who will mole up to 75mm diameter for 8 to 10 meters but will drill 150mm diameter up to 200 meters. Hopefully I'll get a ballpark for how much extra my neighbours tree will cost.
    •  
      CommentAuthordjh
    • CommentTimeJul 13th 2017
     
    Posted By: goodevansDJH - below is one example of the cellular confinement system for information - it may not be what you are imagining.

    Ah, no, when you said a cellular system I was imagining the Bodpave 85 or similar. I haven't seen the cellular subbase before, though it seems like a good idea if you have a uniform depth. How expensive is it? Websites don't seem to give prices for it, which might imply 'reassuringly expensive'! What does it provide that an equivalent layer of plain DtP 3 doesn't?

    I have a company contacting me tomorrow (hopefully) who will mole up to 75mm diameter for 8 to 10 meters but will drill 150mm diameter up to 200 meters. Hopefully I'll get a ballpark for how much extra my neighbours tree will cost.

    Why not contact some of the companies that advertise the service that you want?
    • CommentAuthorgoodevans
    • CommentTimeJul 13th 2017 edited
     
    Posted By: djhWhat does it provide that an equivalent layer of plain DtP 3 doesn't?
    I think the cells and aggregate behave more like a slab and spread the load from vehicles more effectivly. But the main thing it gives me is approval from the tree officer.

    20m2 @200mm deep works out just over £16/m2 - from here..

    http://www.ecomerchant.co.uk/azweb-tree-root-protection-system.html

    Which compared to the price premium for permeable blocks seems like a bargain.

    The trickiest bit is finding a source for 4mm to 20mm no fines angular aggregate in Cambridgeshire.

    Posted By: djhWhy not contact some of the companies that advertise the service that you want?
    I don't care if it's moling or horizontal drilling - whichever is most appropriate - this company does both so hopefully I'll get a balanced opinion - I suspect for the larger bores horizontal drilling is better - particularly if 4 pipes are required in close proximity.
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