Trench digging technique

[blackhorse]

Hi all,

I need to dig an 800mm deep trench for a water pipe through a field. The ground is about 300mm topsoil then thick clay. I'll obviously need to backfill, and want to try and make as clean a job of it as possible. My current plan (with absolutely no experience) is to use a 150mm or 200mm bucket (depending on what the hire company have), and try and remove the bulk of the grass/topsoil and place to one side, then remove the remaining clay and place that to the other side of the trench. The plan being to then backfill the clay first and then the topsoil. Does that sound reasonable?

Where I can imagine I'm going to have a problem is when trying to backfill the clay, which I suspect will be a pain on account of it being big clods rather than a nice loamy/sandy soil which would just almost pour back in. Any techniques for making this part easier?

Thanks very much,
James.

 

[Smiffy]

Hi all,

I need to dig an 800mm deep trench for a water pipe through a field. The ground is about 300mm topsoil then thick clay. I'll obviously need to backfill, and want to try and make as clean a job of it as possible. My current plan (with absolutely no experience) is to use a 150mm or 200mm bucket (depending on what the hire company have), and try and remove the bulk of the grass/topsoil and place to one side, then remove the remaining clay and place that to the other side of the trench. The plan being to then backfill the clay first and then the topsoil. Does that sound reasonable?

Where I can imagine I'm going to have a problem is when trying to backfill the clay, which I suspect will be a pain on account of it being big clods rather than a nice loamy/sandy soil which would just almost pour back in. Any techniques for making this part easier?

Thanks very much,
James.

To get it backfilled better do it in summer as the clay will break up and be relatively easy to reinstate. The placement is personal preference but I prefer to to put both the top soil and subsoil on one side of the trench, but the topsoil further away and the subsoil closer to the trench. This leaves you one side for access for brining in shingle and pipe work. It also means you track along the clear side of the trench and pull the material towards you to reinstate, this means you don't drive on anything and grind it in to the grass. Makes a much cleaner job.

 

[Bri963]

Hi all,

I need to dig an 800mm deep trench for a water pipe through a field. The ground is about 300mm topsoil then thick clay. I'll obviously need to backfill, and want to try and make as clean a job of it as possible. My current plan (with absolutely no experience) is to use a 150mm or 200mm bucket (depending on what the hire company have), and try and remove the bulk of the grass/topsoil and place to one side, then remove the remaining clay and place that to the other side of the trench. The plan being to then backfill the clay first and then the topsoil. Does that sound reasonable?

Where I can imagine I'm going to have a problem is when trying to backfill the clay, which I suspect will be a pain on account of it being big clods rather than a nice loamy/sandy soil which would just almost pour back in. Any techniques for making this part easier?

Thanks very much,
James.

You’re on the right lines James. There’s no easy way to put clay back, you just have to maul it in and flatten it with the back of the bucket. You may be able to track the clay layer flat but 300 deep with a small machine on an angle is a bit sketchy.

I have just quoted for a very similar job, 750 deep, in what we in the Fens call Heavy Black which is very hard-packed peat soil that can be a pig to dig. It’s going to be a 150 bucket, any wider and there’s no room to pile the soil.

 

[Gunners]

A trench rammer helps a lot too, otherwise you'll have a lot left over at the end as it wont all go back in, even if you track it in!

 

[doobin]

I'd use a larger bucket. Go 300 wide and then the digger track will fit properly in the trench to compact it.

I keep meaning to get myself a compaction wheel!

 

[Stroppymonkey]

Narrow buckets can be a pain in clay. 150mm will clag up. Which is why they sell clay spade buckets I guess.
You will be unlikely to get anything smaller than 300mm from hire company.
My 30mm Rhinox QH on mini is wider than 150mm bucket. Makes it slow work digging past 500mm as its rubbing all the time.
Do you need to worry about compaction in a field? Just track it in and leave it high?
Can you not use a trencher?

 

[blackhorse]

To get it backfilled better do it in summer as the clay will break up and be relatively easy to reinstate....

Thanks, Smiffy - unfortunately I need to get it done sooner rather than later. Partly because I need to get sign off from Anglian Water before end of March, and the other because my missus is wanting the water line in place before spring/summer.

You’re on the right lines James. There’s no easy way to put clay back, you just have to maul it in and flatten it with the back of the bucket. You may be able to track the clay layer flat but 300 deep with a small machine on an angle is a bit sketchy.

I have just quoted for a very similar job, 750 deep, in what we in the Fens call Heavy Black which is very hard-packed peat soil that can be a pig to dig. It’s going to be a 150 bucket, any wider and there’s no room to pile the soil.

Thanks, Bri - I think my first priority will be digging a relatively straight line to be honest Then it sounds like it's just going to be best effort in terms of making a tidy job of the reinstatement. We don't have the 'heavy black' you mention, just the standard mustard coloured stuff. It'll be interesting to see how the machine handles it. It's my first time digging with a machine on the land so it'll be a learning experience for sure.

 

[blackhorse]

Narrow buckets can be a pain in clay. 150mm will clag up. Which is why they sell clay spade buckets I guess.
You will be unlikely to get anything smaller than 300mm from hire company.
My 30mm Rhinox QH on mini is wider than 150mm bucket. Makes it slow work digging past 500mm as its rubbing all the time.
Do you need to worry about compaction in a field? Just track it in and leave it high?
Can you not use a trencher?

Generally we do want to avoid compaction, but the particular path that I'm looking to run the trench along is fine to compact as it's effectively a walkway anyway. I honestly didn't know that trenchers existed! I'll do some research and see what's on offer locally for hire.

 

[blackhorse]

I'd use a larger bucket. Go 300 wide and then the digger track will fit properly in the trench to compact it.

I keep meaning to get myself a compaction wheel!

Going 300mm wide would allow me to run some more conduit for armoured electrical cable and fibre optic too (hoping to put an outbuilding up part way along the trench at some point in the future - money allowing).

 

[Canal Navvy]

Trenching in clay you can't be too greedy, if you try to horse it out you'll spend too much time trying to empty the bucket. If you aim to plane it out and not try for a full bucket it'll be quicker in the long run as the backfill material will be easier to handle. I tend to put the turf and topsoil one side and the subsoil the other. When I put the pipe in I walk up the trench and use my arms to drag in enough fill to cover the pipe and stamp it in, after that it's back on the machine to backfill the rest of the subsoil, run a track up to push it down and then back up the line pulling in topsoil and turf before giving a final track over

 

[Furniss]

id go wider too, if there is stone in the back fill and youve no sand to put on first you can nip down and chisel a bit of topsoil in first before the clay ,or put sods close and sweep them in on the ducts first, you might want to consider some warning tape (put in 20cms or so above the ducts) if you're putting in electric and fibre optic, and maybe keep electric and fibre as far away as possible from each other in the trench.

 

[blackhorse]

id go wider too, if there is stone in the back fill and youve no sand to put on first you can nip down and chisel a bit of topsoil in first before the clay ,or put sods close and sweep them in on the ducts first, you might want to consider some warning tape (put in 20cms or so above the ducts) if you're putting in electric and fibre optic, and maybe keep electric and fibre as far away as possible from each other in the trench.

Thanks - I'd planned to put in some Detectamesh so I can find it against in the future. Good point on the fibre/electric cable proximity. I'll stick those opposite sides of the trench if I do end up putting them in.

 

[Stroppymonkey]

Trenching in clay you can't be too greedy, if you try to horse it out you'll spend too much time trying to empty the bucket. If you aim to plane it out and not try for a full bucket it'll be quicker in the long run as the backfill material will be easier to handle. I tend to put the turf and topsoil one side and the subsoil the other. When I put the pipe in I walk up the trench and use my arms to drag in enough fill to cover the pipe and stamp it in, after that it's back on the machine to backfill the rest of the subsoil, run a track up to push it down and then back up the line pulling in topsoil and turf before giving a final track over

If it’s being done to please waterprovider you will need proper back fill 🫣
And marker tape. I like 2 layers of tape. Plastic tape above the granular back fill and then mesh tape between subsoil and topsoil (which is usually about 150mm from surface)

 

[blackhorse]

Trenching in clay you can't be too greedy, if you try to horse it out you'll spend too much time trying to empty the bucket. If you aim to plane it out and not try for a full bucket it'll be quicker in the long run as the backfill material will be easier to handle. I tend to put the turf and topsoil one side and the subsoil the other. When I put the pipe in I walk up the trench and use my arms to drag in enough fill to cover the pipe and stamp it in, after that it's back on the machine to backfill the rest of the subsoil, run a track up to push it down and then back up the line pulling in topsoil and turf before giving a final track over

Really appreciate the input. It sounds like the 300mm bucket is the way forward then, and gently does it.

 

[Stroppymonkey]

Really appreciate the input. It sounds like the 300mm bucket is the way forward then, and gently does it.

And depending on how long a run you need to do.. get as big a machine as you can get away with. Digging a 100mm trench with a small mini is tedious

 

[blackhorse]

If it’s being done to please waterprovider you will need proper back fill 🫣
And marker tape

Yep. Anglian Water have actually been really helpful, and I'm getting them to sign off my approach, including all pipe/connection/adapters etc. before I buy or dig anything. They're happy with the pipe being in a twinwall duct, as long as it's not super stoney, which I'm hoping it won't be......otherwise I'm digging deeper and spending a shedload on sand.

 

[blackhorse]

And depending on how long a run you need to do.. get as big a machine as you can get away with. Digging a 100mm trench with a small mini is tedious

The hire company I'm planning on using (just down the road from me) have a 1.7tn and a 2.5tn excavator. I have no idea how much easier/quicker it'd be with the 2.5tn to be honest......or if the 1.7tn would struggle.

 

[doobin]

The hire company I'm planning on using (just down the road from me) have a 1.7tn and a 2.5tn excavator. I have no idea how much easier/quicker it'd be with the 2.5tn to be honest......or if the 1.7tn would struggle.

Get the 2.5t, negligable difference in cost and will be well on top of the job in clay compared to the 1.7t.

Worth asking if they have a clay spade also.

Or.... go and buy that Bobcat E17 and I have a set of buckets to fit here including a 300mm clay spade for sale....

 

[blackhorse]

Get the 2.5t, negligable difference in cost and will be well on top of the job in clay compared to the 1.7t.

Worth asking if they have a clay spade also.

Or.... go and buy that Bobcat E17 and I have a set of buckets to fit here including a 300mm clay spade for sale....

Thanks - I'll let you know how the viewing goes...assuming it's still available when I speak to them Monday.

 

[blackhorse]

Just to say a big thanks to everyone for the replies. It's really useful to get so much input.

I'll take some photos and drone shots when I get to it, so you can see what a mess I'm making