How to test soil depth above bed rock ?

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  • How to test soil depth above bed rock ?
  • FunkyDunc
    Member

    We have bought a new house with a small garden, with a sloping field behind it.

    We would like to extend the formal garden back in to the field, which would mean creating a level in to the field. However the bed rock might be quite close to the surface.

    I don’t want to go to the expense of and make the mess of using a mini digger if the bed rock is only 1ft below the surface.

    Can you hire anything that will measure the bed rock depth below the surface?

    Ground penetrating radar.

    You’ll need someone to operate it for you.

    nickjb
    Member

    Can’t you just dig a hole with a spade?

    As an aside you may need planning permission for change of use

    munrobiker
    Member

    This is sort of my living.

    Doing it yourself, if you think it’s only a foot deep just dig a pit with a grafting shovel and a pair of scissor shovels. They’ll get you down to about a metre fairly easily.

    Beyond that, you could get a geophysist in to do some GPR as perchy says but it’d be hella expensive, even compared to hiring a mini digger and buying some boards to put the arisings on. A mini digger won’t often get much past 2m though. Another option would be to use a soil sampling hand auger, but they’re a few hundred quid for ones that go much beyond a metre.

    ferrals
    Member

    As Munrobiker said any tech is super expensive… get digging.

    FunkyDunc
    Member

    Looks like digging it is then! To be fair we shouldn’t need to got down more than 1.5m so could just hire the mini digger and use a small bucket at first at various points 🤔

    Premier Icon Squirrel
    Subscriber

    And the Planners will probably want the new surface to be permeable.

    gingerbllr
    Member

    Geo-environmental/geotechnical engineer here – you can hand dig an inspection pit, as munrobiker says.

    Other options include – mini digger if you think its close to surface. Any more than 1.5m/2,0m ish deep and you might struggle. GPR is possible, again if the rock head is closeish to the surface, and it can “see” through the rest of the strata.

    If its deeper than a couple of meters then you’d be looking at a cable percussion drilling rig, around £800/day and a bit messy, or a CPT rig at around £1500 if the formation above the rock is soft enough to push through.

    In your shoes, I’d hand dig a pit with a site spade – dont just do a single pit, do at least 2!

    munrobiker
    Member

    Provided you use the digger to cut the turf off where you want to dig, put it on one side of the hole, then pile up everything else that comes out of the hole on an 8×4 board next to it you’ll be able to put it back in such a way that it’ll look like nothing’s happened.

    DrJ
    Member

    Seismic refraction survey is where it’s at. Stick of dynamite, some geophones, job’s a ggod ‘un.

    Premier Icon wwaswas
    Subscriber

    Can I suggest a series of regularly spaced 6ft by 2ft holes that you don’t replace the turf on when you refill?

    sarawak
    Member

    Why level it?
    I’m assuming that it is sloping upwards. Make a couple of different levels. Use railway sleepers or stone blocks as retaining walls. You can have seated areas, Barbie area, kids play areas. The choice is limitless. Don’t just make it one big flat expanse of poorly maintained grass with a few weedy plants round the edges. You have the opportunity to make something that stands out.

    avdave2
    Member

    Dig a small shallow trench around 6ft long and refill. Report other half as missing.

    rene59
    Member

    Train a mole to dig down verticaly and attach a long lead to measure depth.

    Edukator
    Member

    Hammer seismograph.

    longmover
    Member

    A 3cx or 4cx type backhoe will get you down to 3.5m ish. If it’s only a metre or so you could do some dynamic probes to refusal or continuous SPTs until you reach high N values. Doing SPTs using a small tracked rig would be cleaner than digging with an excavator or cable percussion drilling.

    steve_b77
    Member

    Do you know what the bed rock could be? Is the ground wet & soggy? if it is I’d expect the rock to be close to the surface, or massively permeable sandstone or the like.

    joshvegas
    Member

    How steep is it? Don’t forget you will need a retaining wall or to regrade from the new level. You’ll need to ensure it doesn’t pool when it rains and all the earth will need to go somewhere. Could be way more hassle than its worth.

    Terrace might be a better option?

    Premier Icon WildHunter2009
    Subscriber

    Something like a grid of DCP / TRL probes with a few small hand dug pits to prove that refusal is actually rock would be the cheapest and simplest way. This is probably only worthwhile if it’s genuinely shallow. Slightly more sophisticated would be as longmover says, small dynamic probing rig.

    Premier Icon WildHunter2009
    Subscriber

    Best make sure you have no surprise pipes / drains/ random mystery services. Assuming just because it’s a field there won’t be anything running through it is a mistake many of us have made before ha.

    And to add a cheery note, technically you will require planning permission to change the part of the field to garden use. Which could be tricky.

    Edit: Duh, nickjb said it first…

    Edukator
    Member

    A few ideas.

    Have a look at a geology drift map for where you live. You’re as likely to be on drift as bed rock in many parts of the country. Then have a look at the lie of the land. Is there any rock outcrop? Are there any obvious drift deposits. If there are any trees are they growing vertically or with a curve to indicate down-slope soil creep. What are the gradients and where are you on the slope. If you are in a river valley you are likely to be on river alluvium, on the valley side you’re more likely to be on drift or bed rock. On the top you’re more likely to be on bed rock with a thinner soil covering. There’s a whole lot you can do before even digging a trench.

    The soil profile is rarely soil straight to rock. You go down through oraganic soil to leached mineral soil to mineral soil to altered rock to rock. And the rock itself may be just friable material or something hard.

    I used to have to work out where springs got their water from professionally and most information was there to see if you looked hard enough and knew what you were looking for. Do you know a geologist?

    Premier Icon epicyclo
    Subscriber

    The way I used to do it before deciding if I needed a geotech survey was to go around the area with a pointed steel rod, and bang it into the ground.

    I used rebar or star picket* – the latter being better because there’s a handy tool for extracting it.

    * That’s the Australian term for it – there may be a different name here. It’s a type of fence post.

    Premier Icon lovewookie
    Subscriber

    The way I used to do it before deciding if I needed a geotech survey was to go around the area with a pointed steel rod, and bang it into the ground.

    I used rebar or star picket* – the latter being better because there’s a handy tool for extracting it.

    that’s the sensible way.
    if you can get hold of one (say hire from Van Walt for example) use an auger and probe

    Auger Sets


    like that.

    Houns
    Member

    Whatever you do don’t hire a powered post hole auger, they’re wrist snappers

    Premier Icon fettlin
    Subscriber

    Just to add to the tales of fun and joy, we have our neighbours soak-away’s from their respective cesspits running out into our field.

    Are they uniform length, direction or depth from the surface? that would be too easy!

    I want to replace the fence and gateposts next year, it going to be a minefield……

    natrix
    Member

    Stick of dynamite, some geophones, job’s a ggod ‘un.

    Or get one of these babies!!!!

    https://www.geomatrix.co.uk/land-products/seismic/buffalo-gun/

    sharkbait
    Member

    Make a couple of different levels. Use railway sleepers or stone blocks as retaining walls. You can have seated areas, Barbie area, kids play areas. The choice is limitless.

    As already said, don’t do this unless you get planning for change of use – which I can tell you is very tricky.
    Extending your garden into a field is easy but it’s really obvious when you come to sell.

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