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  1. #1

    Construction advice

    Hi all,

    I am planning on a 3ft dig with a 2.5ft raised section and there are many opinions on how to do this best but thought I would start my own thread for opinions of what I have summarised so far. I will be using pond liner straight on to soil (assuming i can make it safe). I plan for it to be 7ft x 8ft.

    I don't plan to do anything below ground other than dig the hole and plumb in a bottom drain. Above ground i was going to pour a concrete collar (7 inches deep and wide enough for whatever i need next). Then I am either going to lay sleepers on the collar or use blocks on their side with mortar to the required height.

    Does this sound like it would be safe? Is a concrete collar on the edge of a hole stable enough? And would you put the collar in first, then dig, then build sleepers/wall up in that order?

    I really don't want to build up all the way from the bottom of the pond and from what I've read that will obviously work but may be over engineering things. But I also want things to be safe.

    Cheers



  2. #2
    Senior Member Rank = Mature Champion davethefish1's Avatar
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    I used a reinforced concrete collar with sleepers 900mm high, sheer sides. Dug 600mm below collar level.
    If using concrete blocks laid on side 2.5ft high, the weight is about five times that of sleepers.
    Too much for a collar imo.
    But depends on stable ground conditions.
    What do you have Loam/Clay/sand/chalk/waterlogged?

    So i would reduce height to 300mm to 450mm. Sheer sided.
    Concrete block walls need a solid unmoving foundation.
    So i would cast a concrete base and build from the bottom up.
    And if going to that trouble I'd get it fibreglassed....
    Last edited by davethefish1; 20-11-2021 at 12:10 PM.

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  4. #3
    Ok thanks for that. Food for thought. So for ease and cost, use sleepers. Or put a bit more effort and money in to it and go for concrete blocks from the very bottom. Iíll have a think about it and see what the wife thinks about sleepers. If she doesnít like the look of the sleepers, I could always clad it. Cheers


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  5. #4
    Extreme Koi Member Rank = Jussai NickK-UK's Avatar
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    7" deep collar. Given my C35 base if 250mm (9.8") with 10mm rebar, you do have options in terms of making a solid collar. On top of that base is 1.85m of block walling, render, fibreglass and (soon) water.

    Concrete is compression strong but not really sheer strong or stretch strong. Blocks on top interlocked with mortar would provide a way of distributing compression load but the water below will press against the sides - including the collar which could cause it to crack without some additional reinforcement. A small mesh of rebar or even plaster reinforcing mesh could help contain any pressure.
    Blocks - you will need enough surface area on the joints to oppose the force caused by the water pressure outwards.

    I would - I would certainly put a under-liner under the liner itself. It can be a bit of a pain initially as it takes time to bed down before you secure the liner top. So fill and then leave for a period then worry about securing the liner itself under any coping stones etc.

    Also with the blocks - how are you protecting against frost and the elements? You could paint the sides or seal them, but the top need something to keep the water from soaking in and freezing.

    In terms of laying a bottom drain - the trench backfill needs to be compacted down (put pea gravel around the pipe, then pack down). The end out of the pond should have some expansion space (couple of mm). For longer runs you may want 10mm of space for expansion. The pea gravel helps allow the pipe to move without causing it to snap. Where the liner is on top as the trench backfill compresses it will leave a dip and stretch the liner hence the need for a bit of compaction.

    3ft.. going to be a lot of earth, think about the logistics. Digger good, but how is it going to get to the point someone will take it away?
    1700 litres on 50 watts
    Eco Pond 2.0: 13,000 litres, 58W airlifts, 1300l anoxic, Solum 16. No pump.

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  7. #5
    Thanks for all this.

    Digger access would be problematic I think - hard labour and skips would probably be the reality although I would use a digger if I can get one down the side. Iím sure my neighbour manages it for their extension.

    You just blew my mind. I have a lot of prep to do. Which is fine. Iíve set myself 12 months before I even start moving on anything.

    Thanks for the tips


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  9. #6
    Senior Member Rank = Mature Champion davethefish1's Avatar
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    Quote Originally Posted by Benallen2000 View Post
    Ok thanks for that. Food for thought. So for ease and cost, use sleepers. Or put a bit more effort and money in to it and go for concrete blocks from the very bottom. I’ll have a think about it and see what the wife thinks about sleepers. If she doesn’t like the look of the sleepers, I could always clad it. Cheers


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    concrete blocks/fibreglass is the best way no doubt,
    but my access was limited so collar and sleepers,

    sleepers can look good too if you put the effort in...



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  11. #7
    Oh nice. Love the window.


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    Extreme Koi Member Rank = Jussai NickK-UK's Avatar
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    When you plan, create the normal 2D or rough design, however I would advocate getting a laser line level - one that shines across the area. Use a couple of wood stakes at least 3 feet away from the dig, then mark in the laser line and the walls (a stake or two for each wall line). The laser line will be 100% level and that will also be the same as the water. You can then measure down using a long spirit level (so the spirt level is vertical) then use a tape measure to measure down the spirit level.

    Then create a elevation (or more accurately an excavation) design where all the measurements are from that laser line down. That means you want the laser line at least a 12" above the completed wall of the pond.

    Then you have a line with - the ground level at each stake (as the ground varies in depth), the water level, the collar, the dig - including the excavation depths and the pipe laying etc (that means your pipes are level) plus you can plan the water level of your filters (important for drum filters etc) by dropping down from that laser line.

    IMG_9034.jpg

    I did this - and I have about 10mm of difference in level across the entire pond walls, including the drum filter position! I also know that the drum will overflow the waste chute before it overflows the window at the front or any of the walls of the pond.
    1700 litres on 50 watts
    Eco Pond 2.0: 13,000 litres, 58W airlifts, 1300l anoxic, Solum 16. No pump.

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  15. #9
    Quote Originally Posted by Benallen2000 View Post
    Thanks for all this.

    Digger access would be problematic I think - hard labour and skips would probably be the reality although I would use a digger if I can get one down the side. Iím sure my neighbour manages it for their extension.

    You just blew my mind. I have a lot of prep to do. Which is fine. Iíve set myself 12 months before I even start moving on anything.

    Thanks for the tips


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    Kubota .8 ton reduces to 71 cm wide , then expands for steadying,
    Absolute must unless you intend to go body building with a worn out back !!



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  16. #10
    Haha legend. Thanks


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  17. #11
    Extreme Koi Member Rank = Jussai NickK-UK's Avatar
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    I used a Kabut..whatsitsface 0.7t too. Just managed to get it through the gate with the tracks pulled in. Only issue is that you need something just as fast to take the spoil to the skip Two large excavator buckets = 120l wheelbarrow.
    1700 litres on 50 watts
    Eco Pond 2.0: 13,000 litres, 58W airlifts, 1300l anoxic, Solum 16. No pump.

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  19. #12
    Iíve got 5 steps to get down too Construction adviceConstruction advice


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  20. #13
    Quote Originally Posted by Benallen2000 View Post
    Iíve got 5 steps to get down too Construction adviceConstruction advice


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    So did we . Big ramp with lots of support underneath.

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