Deep, narrow hole for a pump. Can a mini digger cope?

[Tony K]

Afternoon all.

My SB, on nigh-impenetrable clay, needs a pump to discharge surface/rain water into the main network.

 

The drainage engineer has designed a standard system whereby an attenuation tank (basically soakaway crates wrapped in plastic) links to a large pump. The tank has got to sit a certain distance below the surface, simply so that it is buried under enough weight not to float up out of the ground. The pump must sit a certain distance beneath the base of the tank, otherwise the system doesn't work:

 

 

 

Thing is, the hole I would need for the pump is about 1.8m deep. I can only get a mini digger to my site, and though we have used a great little machine to dig out a mountain of clay so far for the footings etc, I am concerned that it might not reach so deep into the clay for this job. The spec says it can reach, but I have heard that there may be more to it than what the spec says alone!

 

Has anyone used a mini digger to go that deep? Any problems at all?

 

My other option is to create a more shallow, but equally voluminous tank, which I can do by laying the crates across the site more and into the ground less. That means the pump will only need to go about 1.4m deep, but even that seems no small task for a mini digger.

 

If anyone has any experience on this issue they can share I'd be grateful!

 

 

 

 

[Declan52]

Dig another hole maybe 400 mm deep just a tad wider than the digger with a ramp to get in and out and drive the digger into this hole and then dig what you need. 

[Tony K]

18 minutes ago, Declan52 said:

Dig another hole maybe 400 mm deep just a tad wider than the digger with a ramp to get in and out and drive the digger into this hole and then dig what you need. 

 

Yeah, dig down in stages. Could work, but when I come to put the clay back in the hole the driver is sitting in, it often won't play nicely.

 

More to the point though, would you think a decent mini digger can go to even 1.4 deep in thick clay? Should be OK surely, but I've not gone so deep down with a small machine before. For context, the top level (i.e the garden) has already been reduced by about 60cm from its original level, so I am actually going pretty deep down from original ground, if that makes a difference. 

 

Thanks for the suggestion. 

Edited March 1, 2021 by Tony K

[Dave Jones]

Assuming you have vehicle access then a 3 tonner can ream 3m no problem 

[Tony K]

On 06/03/2021 at 04:14, Dave Jones said:

Assuming you have vehicle access then a 3 tonner can ream 3m no problem 

 

I can only get a mini digger on site, hence the concern. I think I've solved the problem now. I will rearrange the attenuation tank into a more shallow pattern, allowing me to use a 1.5m deep pump. This in turn will only require a 1.7m deep hole. 

[ProDave]

I dug a 2 metre deep test hole not very much larger than the digger bucket using a 3t machine.