Any Civil Engineers/Groundswork people in the house?

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  • Any Civil Engineers/Groundswork people in the house?
  • Premier Icon ir_bandito
    Subscriber

    Picture the scenario.

    I need to dig a 15m wide trench through a 25m tall sandy cliff, down to a depth of about 5m below the beach. The trench comes from about 20m back from the cliff face, effectivly 30m down, all the way through the cliff and out into the beach. I’ve got a very small area either side of the trench accesible, and the land happens to be SSSI, so really don’t want to disturb it too much.

    Is the easiest way to excavate from the top all the way down, or with a long-reach excavator from the beach? Are there excavators in existence that could do this?

    Hopefully someone out there might have some pointers….

    Premier Icon lowey
    Subscriber

    Have you got a picture as I’m struggling to visualise it.

    I do this kind of thing for a living (civils) so will be able to help.

    Premier Icon mikewsmith
    Subscriber

    i was just going to ask for a picture for a laugh ๐Ÿ™‚

    What are you doing it for?

    Premier Icon ads678
    Subscriber

    what is the trench for? 20m long x 15m wide x 25m deep trench to a beach, are you putting a massive boat ramp in?

    Premier Icon ChrisHeath
    Subscriber

    How are you going to support the sides of the excavation, if you haven’t got room to batter it back? If you’re coming 20m back from the cliff face, chances are your excavator will be at the bottom of a 30m deep excavation through a ‘sandy cliff’.

    tarquin
    Member

    You will need to batter it correctly as you dig, if its sandy then it will collapse in like nobodies business.

    How do you intend to support the walls once dug?

    That’s a bloody big hole, have you calculated the amount of earth removed and thought about removal of it from site, thats if at all possible with it being a SSSI it may have to be reinstated to how it was before.

    I’d expect a large excavator of about 30T to have a reach of approximately 7.5m at a guess, plus with a machine that big it will need a lot of room to move, so your benching out will have to be made wider to suit…

    Premier Icon ir_bandito
    Subscriber

    Thanks all.
    Its for a customer who wants to decomission a gas pipeline that comes on shore. We’re looking into options and one is to look at the cost and complexity of digging a massive trench around it to take it out.

    Walls to be supported with sheet piles and cross-bracing as it goes.

    What I need to find out is do suitably-sized excavators actually exist?

    tarquin
    Member

    Maybe you should get in touch with an earthworks contractor and put the work out for tender ๐Ÿ˜‰

    Premier Icon ir_bandito
    Subscriber

    Maybe you should get in touch with an earthworks contractor and put the work out for tender

    We will if they go down this route, but its all concept ideas at the moment.

    Premier Icon ir_bandito
    Subscriber

    Oh, they do exist….

    Premier Icon mikewsmith
    Subscriber

    no please draw a pic and the take a pic of it and post it ๐Ÿ™‚

    after that contact the pro’s.

    I’m assuming a really high powered truck and a massive magnet have already been discounted?

    tarquin
    Member

    What does the Haynes manual say, removal is the opposite of installation! Simple, just find out what they did originally and do that in reverse.

    slowoldgit
    Member

    It’s not a geological SSSI is it?

    marcus
    Member

    I’ll happily provide you with an appropriate solution if you instruct me to act as your geotechnical consultant ??

    Premier Icon ir_bandito
    Subscriber

    Thanks again, I knew STW would help.

    dynamite is surely the best option….

    Premier Icon crispo
    Subscriber

    +1 for go to a ground works contractor.

    Wouldn’t have thought that many would have ready access to an excavator with a reach like that in the picture above. Most should get 14m infront reach and maybe 9m down but you obviously have a big bit in the middle out of reach.

    I’d think your bet bet would be to dig down through the cliff with the excavator working in the trench made, obviously with proper temporary works in place (properly designed) then as you tech down to the beach side dig that with an excavator in top. Once again temp works is key due to the probable nature of the ground.

    As mentioned that’s a lot of earth to shift. A rough guess would say 7500 cube meters, if you cannot leave that on site then that’s 800 odd wagon loads!

    Premier Icon bigjim
    Subscriber

    many alarm bells ringing, but if it is a SSSI, you’re going to have to do a bit more than ask for advice on STW!

    Premier Icon 40mpg
    Subscriber

    Sheet pile the sides to retain the sand, cross-propped to minimise pile length and avoid any cantilever action on the piles which will be difficult to achieve in sand.

    Excavate to temporary spoil heaps on the beach.

    Remove pipe

    Reinstate fill

    Remove sheet piles

    Make due allowance for licences, environmental consulatnt fees, enviro report etc.

    Consider tidal and weather effect on programme!

    Greybeard
    Member

    I’d try to find out how the pipeline was put in; the ground will be disturbed if a trench was used. I don’t see that you could justify digging in a virgin SSSI if there’s another way.

    tops 5
    Member

    I would reduce the level around the trench (within 7.5m of dig depth) with a dozer, the dozer will be able to push everything back and make good once complete – you will need the method statement/planning done by someone who knows what they’re doing tho!

    Edit: Just read OP properly that is one big hole! Cannot be done without a lot of disturbance

    breatheeasy
    Member

    Can you not just stick a really really big cork in both ends of the pipe you want to decommision?

    Premier Icon BigJohn
    Subscriber

    Put the pipe on ebay with buyer collect.

    tops 5
    Member

    Send a new plastic one up (pipe bursting?) and then cap the ends of the new “inner” pipe?

    Premier Icon ir_bandito
    Subscriber

    There is actuually some good advice in there.
    If it helps, the scheme has been devised by someone with lots of experience of these things, we’re awre of licenses, SSSI concerns, supporting the earth etc, and yes, it will obviously be finalised by a professional earthworks contractor.

    All I really wanted to know is where do the diggers go? Top or bottom?

    ebay suggestion is my favourite so far…

    Premier Icon psling
    Subscriber

    Its for a customer who wants to decomission a gas pipeline that comes on shore. We’re looking into options and one is to look at the cost and complexity of digging a massive trench around it to take it out.

    Is another option to isolate it and seal it off leaving it in-situ? Would probably be a lot less hassle ๐Ÿ™‚

    kevj
    Member

    The sheet pile wall should be designed such that the excavation plant is at the top.

    Be aware you will need a stone piling mat (which also needs designing) for the piling rig as they won’t go near the site otherwise.

    I used to do this sort of thing in my previous job and can point you in the direction of good, experienced local firms if you wish (assuming NE coast)

    Premier Icon andyha
    Subscriber

    Use precast concrete ring segments, sink a shaft on top of the pipe, theh dig out with a mini digger and draw material away using a crane/skip. Within the circular shaft it is safe work and will reduce the dig and footprint. Once you get to the pipe level fill it will foamed concrete, then fill in the hole and fannys your aunt.

    tops 5
    Member

    Bang on Andyha – we once built a tank using this top down method (about 15M deep).

    Dug down as far as possible with 40T excavator and then lifted in mini digger. Concrete was wedge shaped in section so that downward pressure forced it against the sides of the excavation- we used insitu concrete tho as it didn’r need to be reinforced and pre-cast lead times or too long for bespoke sizes – also precast sections would be massive for Bandito’s dig

    tymbian
    Member

    Cut the pipeline up and remove bit by bit by crane.

    tops 5
    Member

    Cut the pipeline up and remove bit by bit by crane.

    You would still need to dig the hole to cut it and sling it?

    Kit
    Member

    You know when you find a bit wire in the ground and you just pull it out, like a reverse cheese wire….

    ๐Ÿ˜‰

    Premier Icon ir_bandito
    Subscriber

    Is another option to isolate it and seal it off leaving it in-situ?

    Yes it is, but that leaves long-term resonsibilities to worry about.

    Cut the pipeline up and remove bit by bit by crane.

    That’s also been considered, and is the only way to get the pipe out once the trench is dug due to the cross-bracing of the sheet-piles and the pipe being 30m underground….

    Cheers for the pointer about the piling mat kevj. Its not NE, its down south. Proabably shouldn’t say much more on a public forum…

    Premier Icon andyha
    Subscriber

    Macrete

    Above is a link the system which I have have used to form shafts to tunnel under a tunnel, I have also used diaphragm walling but this was to depths of 35m which maybe a bit deeper than required.

    If you only need to decomission the pipe there should be no reason to remove the whole pipe section unless required to do so by EA or LA or whomever owns the land.

    Premier Icon cr500dom
    Subscriber

    you could look at the way they do Oil and gas riser decomissioning

    Pass a waterjet/garnet cutting head down the pipe and cut from inside out, lift pipe out from above
    Pull remaining pipe out from beach side

    Minimal environmental impact, minimal clean up

    EDIT, if you want to speak to someone about the possibilities of this method send me a pm and I`ll point you in the right direction

    Premier Icon 40mpg
    Subscriber

    Be aware you will need a stone piling mat

    No you don’t. Vibro sheet pile wit the vibro head on a tracked excavator arm. Speak to Dawson Wam or similar for info. Vibro will be easy to install in running sand, but vibration monitoring will be necessary as sand transmits the vibration more than most soils. Will have to be OK’d with enviro chaps first.

    (use more PPE than this lot though)

    Premier Icon ir_bandito
    Subscriber

    Pass a waterjet/garnet cutting head down the pipe and cut from inside out, lift pipe out from above
    Pull remaining pipe out from beach side

    that’s another option that is being considered.

    We’re presenting all options to the customer, including digging it out. I just wanted to know about the diggers!

    Premier Icon pictonroad
    Subscriber

    File under too difficult or expensive. Clean it and fill it it with foam concrete, that’s a flippin’ horrible sounding job to remove it.

    tymbian
    Member

    Oooh, I love a project.

    Even if you could find an excavator to dig 30m you’ll still need to shore up the sides. You’ll probably have to shore up in stages say start at 20m wide then 10m down 10m wide til the pipe is reached. Might as well use an excavator with a largest bucket to save time as opposed to 30m reach and small bucket. Load onto conveyor to take away, remove pipe, reverse conveyor to fill in. Simples!

    marcus
    Member

    At 5m below beach level, beware of groundwater blowing the base of your excavation. And good luck with driving 30m long sheet piles into sand competent enough to form a ‘cliff’.

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