# Forum Home Renovation Structural Renovation  Sump Pit Construction

## HandyDaddy

Hi Guys 
Please tell me if I'm making a big mistake. 
I am building a sump pit for my stormwater collection. The stormwater drains from an extension I am building will run into the pit and  then the water will be pumped up into a 25,000 litre rainwater tank.  
To construct the pit I was first of all going to buy a pre-cast concrete pit 600x600x1200mm. However with the recent winter rainfall, my ground is now pretty boggy and I cant get a lorry in to lift a precast pit into an excavated hole. The precast pit weighs about a ton and I have no other way to handle it. So I got to thinking .... 
I have about a thousand old bricks onsite and so I thought I should just brick up the pit instead with second hand bricks. This seems like the ideal solution to me. I get to dispose of some of these bricks and save myself about $400 in the process. 
It seems like a good idea, but is there any good reason why this would be a bad mistake. 
Thanks 
Mike

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## sundancewfs

I would be concerned about the structural strength. It would need serious reinforcing to make sure the walls don't collapse in, with the force of the earth around them.
For my storm water pit, I used Atlantis flow tank modules. http://www.renovateforum.com/f176/ic...project-76617/
If you scroll down to the bottom of the link, You will see the product I mean.
I used ours as a soak well, but they can be tanked as well and pumped from, using a liner.

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## Frankster

Hi There 
Will this stormwater pit you propose have any overflow to a water table or will overflowing this pit = flooding :Shock: ? I'd assume there is no spillway hence the size of pit required to allow for deluges where the pump can't keep up with the rate it fills. 
I agree with previous poster that a brick constructed pit would be no good as it would be difficult to build it with enough inherent strength as to not crack. Reinforced concrete is the way to go. Casting a concrete pit in situ is a way that perhaps you should consider as it may better suit you. First dig the hole, cast the bottom floor of the pit first with the steel reinforcemnt mesh "cage" in place, then cast the walls next with plywood or MDF and plastic membrane formwork as the temporary inner liner. Keep in mind the weight of the concrete the liner must hold back so it needs to be strong and cross braced. The PVC supply pipe can even be cast in, you just need to think about how to get the formwork out with pipework in place. I'm sure there are plety of examples of how to do this on the net. A few mates (or kids) to help, doing loads on the cement mixer.. That's how I've done it anyway. Once for a stormwater pit just as above, also once did a garage mechanic's pit with shutter formwork but trucked in the concrete for walls (4 cubic metres) except the floor which I did with a mixer... 
Cheers

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## HandyDaddy

Hi Guys 
Thanks for the advice. 
I,m under pressure to get this pit built so decided to brick up but took on sundancewfs' advice, and I put 8 rods of 12mm reo down through the holes in the extruded bricks to strengthen it.  
Before I started I had to pump out the hole I had dug. There was about 800mm of water collected in it. I cleaned it up and poured in a concrete base, but a few hours later that was also covered in water. I left it for a few days and again pumped out about 800mm of water to get down to the base, which had set hard enough to continue building, and started to brick up. I only had time to complete a few courses of brick but the water seaping into the hole from the surrounding ground was constantly finding its way through the morter joints and continuing to seep into the hole. I've battled on and now have about 600mm of bricked up pit, but am totally disillusioned with it. Because the ground is so wet the morter I am laying is just becoming slurry because of the constant trickle of water from the surrounding pit walls.  
Apart from concerns about the final strength of the pit, as you guys quite rightly pointed out, I am now also concerned that I'll never have clean water in this pit because of the poor morter joints allowing mud to trickle in from the surrounding ground. 
I considered ripping down the brickwork today and buying a plastic pit, such as the everhard 600x600 with a fer risers, however I can simply see that being lifted up out of the ground due to hydrostatic pressure an the hole around the plastic pit continues to fill with ground water.  Aarrghhh! 
I have considered forming up and casting a concrete pit in situ as Frankster suggested, but will the groundwater just destroy that also as it seaps into the mix from the surrounding walls and prevents the mix from curing properly? 
I now considering as a last resort, rerouting my stormwater drains to a temporary outlet until the spring when I can get a lorry in with a precast concrete pit and drop it straight in the hole. 
By the way, the pit is 1200mm deep because applying a 1:100 fall, the strormwater drains from the  house are 600mm below ground by the time they get to the pit. There will be an overflow outlet at the top of the pit which runs off to an open drain further down my garden and then into a dam, so flooding should not be a risk. 
Also my soil is mad up of about 400mm top soil/sandy silt and then clay below. 
Please - any advice on how to beat this damn ground water issue and build this pit successfully would be greatly appreciated. 
Mike

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## Frankster

Hi Mike 
Sounds like you didn't put down a layer of plastic before bricking up.  
The only way I could think of dealing with the water seepage problem you have now would be to dig even deeper than you have already to one side of the hole, forming a new temporary sump for a submersible pump whilst you finish construction.  
Are you planning to render the inner of the brick pit? A few layers of chicken wire clouted into your mortar courses, a coat of bondcrete and a strong mortar render would strengthen the walls up considerably. 
 Cheers - Frank

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## HandyDaddy

No - theres was no plastic layed in the hole before bricking up. :Doh:  
I guess the best thing to do is rip it down, put in a temporary stormwater outlet and come back to this mess when the weather improves. 
By the way - if theres anyone reading this from the Melbourne South East Water Authority, I know why your resevoirs are only 30% full. Its because all your water is in my garden

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