[danielpcraze]

Sorry for the long winded post, any insight is appreciated:
I discovered a pit 3' in diameter and 7' deep (dry well?) in my back yard. This was discovered because I had roofers replace my roof and they set the dumpster on my back patio/concrete slab. The concrete slab cracked and that is what initiated further investigation. You can see from the pictures that part of the pit is exposed on the grass (this was covered with 2'square paving bricks, so it wasn't obvious that there was a pit beneath it!).
Now that I have a cracked slab, I would like to cut the cracked slab out, fill the pit with gravel, and pour a new slab (extending it out about 2' into the yard so that the entire slab covers the pit as well as to allow more room for my outdoor kitchen). Since this slab will become the foundation for my outdoor kitchen, I am hesitant about leaving the hole unfilled. On the other hand, I'm concerned that filling the pit will cause drainage issues...should this be a concern? There are no inflow pipes into the pit, but obviously water finds its way during heavy rain storms.
My yard slopes towards the house, and the concrete slab/patio slopes away from the house (i.e. right now this pit is a low spot between the house and the yard)
My concrete slab/patio is about 12' wide - which makes the edge of the drywell closest to the house about 10' away from the house/foundation

 

[Windows on Wash]

Pics didn't come through. You need a couple more posts.

 

[Windows on Wash]

Generally speaking, I think they should be filled.

 

[stadry]

fill w/cheapest granular fill you can find,,, unfortunately you won't be able to do it in compacted 'lifts' @ 7' but do the best you can

 

[danielpcraze]

Thanks Stadry.
My thought is that I will break up the concrete that I'm removing (the cracked slab) into as small of pieces as my BFH will accomplish and throw those down the pit. After which, I will bring in some washed gravel to fill the rest of the way. I'm not sure what's meant by 'compacted lifts' but it does bring up another question... If I fill with gravel, do I have to worry about compaction over time? (i.e. in 15 years will I have an air void underneath my new slab because this gravel settled, possibly resulting in my newly poured slab developing a crack?)

 

[stadry]

' lifts ' = layers,,, you could fill w/#57 stone but its probably more $$$,,, yes, there's be settling over the years as water leaches into the pit so no square dancing on the new conc :surprise: put some #4 rebar into the new conc - maybe $14 worth

 

[AllanJ]

The dry well should either be kept empty and equipped with a removable lid, or filled in, tamped, and allowed to be covered over.

A dry well has limited ability to dissipate ponding storm water. Whether or not you fill it you need to determine whether you will have a flooding problem nearby and figure out how to solve that.

 

[SeniorSitizen]

Each time i read anything about a pit of any depth over a couple ft. deep i can't help but recall the TV rescue episode of baby Jessica.

 

[landfillwizard]

Look into flowable fill. Use it on a project and once the water settled we were able to put footer over the material. 10 years later there were not cracks in a CMU wall.

 

[lenaitch]

It looks to me like an old well that has gone dry rather than what I know as a 'drywell'. I would fill it in, compacted as best you can. One problem with using busted concrete is that it will leave voids than may promote settling of finer fill.

 

[DexterII]

I don't see any lines running into it so would have no concern regarding drainage, and would fill it with pea as it runs at something like 95%, negating any concern with compacting it. The broken concrete could go back in the hole, but I would toss it in as you fill, rather than a pile in the bottom, to minimize voids. Less whatever the concrete takes up, you're looking at close to two yards of fill, so probably more than you want to haul home in bags but little enough that you'd probably have a significant delivery fee for a small load.

 

[stadry]

1st off, its not a 'dry well' but a dug well - note the walls ? flowable fill costs mucho MORE $$$ than granular,,, is it better than granular or #57 stone ? certainly but at what cost ? it'll take 1.83cy of flowable fill - here its $145cy w/5cy minimum = $ 725,,, i'd guess for that much $ you could get 20cy of either granular fill OR #57 stone,,, another point - can the transit truck back up to discharge into the hole or not ? no means you either rent a conc pump ( $ 900 min ), bobcat, OR 11 amigos w/wheelbarrows @ $150day,,, just my arithmetic & thinking

 

[landfillwizard]

1st off, its not a 'dry well' but a dug well - note the walls ? flowable fill costs mucho MORE $$$ than granular,,, is it better than granular or #57 stone ? certainly but at what cost ? it'll take 1.83cy of flowable fill - here its $145cy w/5cy minimum = $ 725,,, i'd guess for that much $ you could get 20cy of either granular fill OR #57 stone,,, another point - can the transit truck back up to discharge into the hole or not ? no means you either rent a conc pump ( $ 900 min ), bobcat, OR 11 amigos w/wheelbarrows @ $150day,,, just my arithmetic & thinking

WOW! The price sure went up on flowable fill. Last time I used it on a project it was about half the cost. How time flies and prices rise. I was thinking that if he was building over the well that I woulds want to seal the shaft and raise the top so the water would run away from the excavation. Granular fill would tend to make the old well an area for water to settle.